Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/23/16
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
816 PM CDT THU SEP 22 2016
.UPDATE...
Issued at 814 PM CDT THU SEP 22 2016
Forecast appears on track. Patchy fog/drizzle should continue
overnight with low cigs in place or developing. WAA kicks in late
with HRRR still indicating increasing coverage of
rain/thundershowers late. Temperatures look fine for now.
&&
.SHORT TERM...(This Evening through Saturday Night)
Issued at 328 PM CDT THU SEP 22 2016
The models have been consistent and agree well through the short
term. The large upper level low pressure trough over the southwest
U.S. will slowly lift northeast and into Southern Canada/Northern ND
through Saturday night. In response to this, a warm front will lift
northward across our cwa tonight and Friday. The areas of drizzle
and fog along with thick stratus clouds will likely continue into
the night with the low and mid level waa. Radar was showing many
weak returns this afternoon. The webcams and obs were also showing
some drizzle/light showers. Also, have in chances of showers and
thunderstorms for tonight and Friday with the waa. As the surface
low pressure area moves into SD Friday evening and then onto the
north into Saturday, a dry line/cool front in behind will sweep east
across our cwa Saturday and Saturday evening. Showers and storms may
develop along this boundary as it moves quickly east. Saturday night
looks to be dry and breezy with wrap around clouds beginning to
advect into the region from the northwest. After a cool day today,
it will be much warmer on Friday as the low clouds break up/move
north and we mix out the warmer ll air along with some sunshine.
Locations in our sw cwa may see the mid 80s. Saturday should become
mostly sunny in the dry slot of the upper low with highs mostly in
the 70s.
.LONG TERM...(Sunday through Thursday)
Issued at 328 PM CDT THU SEP 22 2016
Period starts off with an upper level low over the region. Area will
be on the cold air advection side of the low Sunday into Monday,
with cool temperatures, breezy winds, and potential for showers.
Although, there are still some differences noted amongst the models
regarding the exact track of the upper low, which does influence
shower potential across the area. For right now, will keep low
chances in the forecast but did increase chances a bit Sunday
afternoon. Removed POPs across the eastern CWA towards the end of
the period, which seemed to be hanging onto precip chances too long
as the upper low departed. The GFS keeps the low around much longer
than the EC, so SuperBlend is picking up on this solution a bit. If
the GFS starts to trend more towards the EC, then POPs can likely be
removed for Monday night and perhaps even Monday.
Looking towards the middle of next week, there will be some cool
overnight lows as a surface ridge sets up over the area. Overall,
the air mass itself is not terribly chilly, with 850MB temps in the
+5C to +10C range. But, given the longer nights, any length of time
under clear skies and light winds will allow temps to tumble. For
right now, left inherited Superblend temps, but will monitor for
potential lowering in the coming days.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 615 PM CDT THU SEP 22 2016
A mix of mvfr/ifr cigs will continue across the region through
tonight and into Friday morning. Meanwhile, a mix of vfr/mvfr
vsbys are expected due to fog and patchy drizzle. Late tonight
there is a better chance of showers and isolated thunderstorms as
a frontal boundary begins lifting north across the state.
&&
.ABR Watches/Warnings/Advisories...
SD...NONE.
MN...NONE.
&&
$$
UPDATE...TDK
SHORT TERM...Mohr
LONG TERM...TMT
AVIATION...TDK
Area Forecast Discussion
National Weather Service Wakefield VA
1051 PM EDT THU SEP 22 2016
.SYNOPSIS...
Low pressure along with a weak frontal boundary will remain
stalled along or just off the Southeast and Mid Atlantic coast
through Friday morning. High pressure builds over the local area
later Friday into Saturday morning. A backdoor cold front drops
across the region during Saturday. The center of high pressure
slides into southeast Canada during Sunday.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Update...
Showers are diminishing across south central VA this evening as
another area of precip tries to rotate into interior NE NC. This
particular swath of light to moderate rain showers will continue
rotating into this area and is expected to remain scattered
throughout the evening and overnight hours. Isolated/embedded
thunder is possible in interior NE NC, however this minor threat
will come to an end later this evening. Otherwise, increased sky
cover the rest of tonight while temps/dewpoints are on track with
ongoing forecast.
Previous discussion (429 PM)...
Late this aftn, areas of showers continued to affect cntrl, SE,
and scntrl VA, and NE NC, with a few showers still producing
heavy downpours. Otherwise, there was a little more brightening of
the sky ovr the CWA, with even some sunshine ovr extrm Nrn/NW
counties and ovr NE NC counties. As a result, temps climbed into
the mid 70s to lower 80s most areas. Lingering low pressure and a
frontal boundary along or just off the SE and Mid Atlc coast, will
maintain the chc for at least sctd showers ovr the srn/se half of
the region this evening into Fri morning. Heavier downpours will
diminish during this evening. Lows will range fm the lower 60s to
the lower 70s.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
The combination of nrn stream energy and the coastal
low/associated upr trough weakening, will finally result in
decreasing pops and rain chcs ending ovr the sse Fri into Fri
night. Will carry slight chc to low end chc pops (20-30%) acrs
srn/se areas only during Fri. Surface high pressure will build
over the region Fri night into Sat morning resulting in dry wx
everywhere. Highs on Fri will range fm the upr 70s to mid 80s.
Lows Fri night in the mid 60s to near 70. A backdoor cold front
will drop acrs the region during Sat, and the cntr of sfc hi
pressure will bld twd SE Canada by Sun morning. Will maintain dry
wx during this period, with generally a partly sunny sky on Sat.
Highs will range fm the upr 70s to lower 80s acrs most of the
area. Expect more clouds ovr the Piedmont Sat night. Lows will
range fm the mid 50s to the mid 60s.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Medium range period begins Sunday with an amplified upper level
ridge/trough pattern, the ridge axis being centered across the
TN/OH Valley with a deep trough over Atlantic Canada. This much
the GFS/ECMWf and ensembles are in good agreement with. By Monday,
the models really begin to diverge however, the GFS and GEFS mean
being much stronger than the ECMWF with an upstream trough over
the upper midwest by Mon/Tue. this would lead to more of a strong
blocking pattern that would keep the eastward progression of upper
ridge axis much slower, becoming aligned along the east coast by
late Tue/Wed. The CMC is even slower to push the upper ridge off
to the east than the GFS/GEFS. Bottom line is a lot of model
uncertainty beyond Monday. For Sunday/Mon, surface high pressure
is progged to become centered over eastern Canada with a piece of
the High ridging down into the northern mid-Atlantic states by
Monday. Deep moisture will be pushed south of the local area, but
expect more clouds than sunshine for Sunday (except over the
eastern shore where more sunshine should prevail). Have also
lingered 20% POPS for much of the area Sunday, shifting to the SW
and far W zones Sun night/Mon. Highs will average in the low-mid
70s with lows in the upper 50s to mid 60s Sun/Mon. Did more a
broad-brushed 20% POP by late Tue-Thu as high pressure becomes
centered somewhere off the NE/northern mid-Atlantic coast and
deeper moisture and a slow moving front gradually approach from
the W. Highs will avg 75-80 F Tue-Thu with lows mainly in the
60-65 F range.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Low pressure continues to sit off the South Carolina coast, bringing
the region unsettled conditions. Abundant low level moisture and
onshore flow will promote widespread IFR stratus...especially in the
southeast (PHF ORF ECG) with some IFR vsby. This will be slow to
improve Friday morning. Precipitation is diminishing but will still
be possible southeast portions...especially at ECG.
More favorable conditions are expected by midday Friday with VFR
conditions and mainly dry weather across the area as the
aforementioned low weakens.
OUTLOOK...A cold front sags south through the Mid Atlantic States
durIng the weekend. High pressure builds from the north but
weakens toward midweek. It will be mainly dry through the outlook
period and despite an onshore flow...VFR conditions are expected
to dominate.
&&
.MARINE...
10 pm update...
Due to an increase in the wind over the Bay and adjacent coastal
waters...extended the SCA that was set to expire at Midnight to 4
AM EDT. HRRR handling the winds best.
Latest obs reflect ENE flow across the waters as Pressure
gradient remains compressed between high pressure well north into
New England and weakening low pressure lingering along/just off
the SE coast. Seas have dropped off to 4 ft or less for NC waters
so have cancelled the SCA headline there (remaining in effect for
the rest of the coastal waters and mouth of the Bay). Winds of
15kt gradually drop off from late this aftn through tonight as
pressure gradient slackens a bit further.
Winds turn more northerly and pick up a bit by Fri night as weak low
finally nudges offshore. A weak Cold front drops across the waters
late Friday Night into Saturday, stalling just south of the waters
Sat night and Sunday before sliding south into the Carolinas on
Monday. CAA surge behind the front appears minimal...but SCA for
hazardous seas possible over the weekend as longer period swell
begins to mix in Friday night through Sunday.
&&
.HYDROLOGY...
The Cashie River at Windsor crested at 15.0 ft late this
morning...with the most current level at 14.5 ft and slowly
falling as of 715 PM this evening. This water level is still
within major flood stage, which begins at 13 ft. Although light
rain showers are expected to continue overnight through Friday
afternoon before ending, the Cashie River near Windsor is forecast
to steadily fall over the next several days...possibly dropping
below flood stage completely by roughly Sunday afternoon.
&&
.TIDES/COASTAL FLOODING...
As of 17Z, tidal departures continue to avg +0.5 to 1.0 ft over
the marine area, but no tidal flooding is occurring and no
advisories are needed at this time. Will continue to monitor
however, as tidal anomalies may build nwd through the Bay by later
this aftn which could lead to some marginal tidal flooding by this
evening farther up into the Bay.
Moderate risk for Rips expected for Thu.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory until 10 AM EDT Friday for ANZ650-652-654.
Small Craft Advisory until 4 AM EDT Friday for ANZ634-656.
&&
$$
SYNOPSIS...TMG
NEAR TERM...BMD/TMG
SHORT TERM...JDM/TMG
LONG TERM...LKB
AVIATION...LSA
MARINE...LKB/LSA
HYDROLOGY...
TIDES/COASTAL FLOODING...
Area Forecast Discussion
National Weather Service La Crosse WI
830 PM CDT Thu Sep 22 2016
.UPDATE...
Issued at 830 PM CDT Thu Sep 22 2016
The trends in the hi-res meso scale models have been consistent
through the afternoon into this evening of the convection that
develops tonight north of the stalled front across Iowa to
primarily be confined to northeast Iowa into southwest Wisconsin.
Activity has been developing north of this front along Highways
20 and 30 across Iowa, which is close to what the HRRR has been
suggesting. While locations in the Interstate 90 corridor may see
some rain overnight, not expecting it to be all that heavy so
opted to trim back the flash flood watch to just northeast Iowa
and southwest Wisconsin.
&&
.SHORT TERM...(Tonight and Friday)
Issued at 318 PM CDT Thu Sep 22 2016
Rainfall records continue to be set and rivers continue to rise.
We have reached a vulnerable point where forecast rainfall is of
utmost importance. Good news is there may be some relief in sight.
We continue to watch progression of large upper low moving through
western U.S. Unlike past few days, minimal signs of an upstream
short wave to focus low level response into boundary that divides
very moist airmass to the south and drier, cooler airmass north.
Combined with backing flow as upper trough digs in west, seeing
signs in short term model data that main moisture transport and
focus will be shifting more west for tonight.
Nonetheless, primed airmass remains along southern tier with higher
precipitable water values and some convergence. Convection has
slowly been on the increase closer to Highway 20 area in Iowa,
closer to CAPE gradient region. As the evening goes on, would expect
this focus to gradually shift north unless convection becomes
extensive enough to hold boundary where it is at. Still concerned if
convection does spread north, we could see another 1-2" of rain so
will keep Flash Flood Watch going at least into Friday to cover any
threat. Given how saturated things are, anything over a half inch
could pose a problem.
On Friday, as upper flow continues to back and becomes more
southerly, may see remaining area of elevated convection gradually
shift north and east as it dissipates. Banking on coverage being on
the lighter side with loss of forcing. Also hoping this leads us
into a period of dry weather and flood headlines can be cleaned up a
bit.
.LONG TERM...(Friday night through Thursday)
Issued at 318 PM CDT Thu Sep 22 2016
As previously mentioned upper low lifts northeast over the weekend,
could see lingering dry spell Friday night into Saturday ahead of
approaching cold front. Models in fair agreement bringing elongated
north-south band of rain with cold front passage Saturday night into
Sunday. Some model differences on timing with 22.12z NAM the fastest
to move rain through, and the GFS/ECMWF more alike holding it back
more, but still not as bad as previous model runs had. Convection
may not be as intense as earlier this week, but prolonged (?) which
could bring more concern for areas hard hit by flooding. Will
certainly have to watch how this plays out and future flood watches
may be needed.
Now for the really good news. Drier flow regime looks in the offing
for much of next week, although some differences in medium range
guidance.
22.12z ECMWF is far more progressive sweeping upper low by and
northwest flow sets up with eventual upper ridge building in. GFS is
a bit slower with this evolution and swings upper low into Great
Lakes. This might not generate as much rain but may hold back
temperatures far more than ECMWF. Blends of operational models
suggests a small chance of rain into mid week but we could see a lot
of dry time in there.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 604 PM CDT Thu Sep 22 2016
A weak boundary was across southern Minnesota into northeast
Wisconsin late this afternoon with the main surface boundary
across central Iowa into southeast Wisconsin. The convection so
far as been just north of the southern boundary and well south of
both airports. A mixed bag of ceilings along and north of the
northern boundary with VFR going down to MVFR. Plan to start both
TAFs with VFR conditions and then go down to MVFR ceilings by the
middle of the evening. Some potential, all be it a small one, that
some showers could impact both airports overnight once the low
level jet starts to interact with the southern front. Think most
of this activity should stay to the south though and have just
shown a VCSH overnight. More likely to occur is the ceilings going
down to IFR at KRST overnight with some MVFR fog forming at both
airports. The winds aloft off the 22.18Z NAM forecast soundings
look too strong to allow much of visibility restriction. The
forecast soundings do not show much potential for the ceilings to
improve Friday so will only show some minor improvements through
the day.
&&
.HYDROLOGY...
Issued at 318 PM CDT Thu Sep 22 2016
Many areas saw 4 to nearly 12 inches of rain last few days.
Combined with recent wet periods most area rivers into flood.
Potential for another 1 or 2 inches tonight could generate more
problems but confidence in that is low given weaker forcing tonight
and boundary further south. Concerns are shifting from immediate
flash flood threat to high water or areal concerns, along with river
flooding.
Also look for continued rises on the mainstem of the Mississippi
River going into next week, which could lead to an increase in flood
warnings there. Water levels will be fall slower than normal as well
given how saturated everything is.
&&
.CLIMATE...
Issued at 318 PM CDT Thu Sep 22 2016
La Crosse WI...
Top September rainfalls...
1. 10.87 inches in 1881
2. 10.52 inches in 1965
3. 10.33 inches in 2016
4. 10.01 inches in 1884
5. 9.84 inches in 1901
Rochester MN...
Top September rainfalls...
1. 10.50 inches in 1986
2. 9.95 inches in 2010
3. 8.96 inches in 2016
4. 8.08 inches in 1978
5. 7.95 inches in 1938
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Flash Flood Watch through Friday afternoon for WIZ054-055-061.
MN...None.
IA...Flash Flood Watch through Friday afternoon for IAZ008>011-018-
019-029-030.
&&
$$
UPDATE...04
SHORT TERM...SHEA
LONG TERM...SHEA
AVIATION...04
HYDROLOGY...SHEA
CLIMATE...SHEA
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
700 PM CDT Thu Sep 22 2016
.SHORT TERM.../This evening through Friday/
Issued at 307 PM CDT Thu Sep 22 2016
The situation is still conducive for heavy rains tonight but
hopefully not to the same extent as yesterday. Water vapor imagery
does not show the moisture fetch to the same degree as was shown
Wednesday, but there is a decided back edge to the vertical motion
passing through the Plains into western KS/NE which should aid lift
into the night. This has resulted in weak but broad mid level
kinematic forcing with a ribbon of somewhat favorable mid level temp
and theta-e lapse rates from KS into IA. Thermodynamically the
forcing is somewhat better with 850/700mb warm advection noted into
IA and 0-2km moisture pooling into our baroclinic zone as well. 20Z
surface analysis shows at least two boundaries, one tied into low
pressure near Lincoln between Red Oak and Atlantic, another farther
northeast through the Des Moines metro area more associated with
previous MCS outflow and likely another from Estherville to Grinnell
with seems to be immediately associated with the weak MCS. This
will provide for ample isentropic lift into the night, but the flow
is weaker along the 305K inflow surface vs last night, down to 15-
30kts. RAP elevated instability layers suggest elevated CAPEs will
reach uncapped 1500 j/kg later tonight sustaining additional MCS
development. There could be a few strong to severe storms, but
overall the Marginal Risk seems fine due to reduced effective shear.
.LONG TERM.../Friday night through Thursday/
Issued at 307 PM CDT Thu Sep 22 2016
Expecting some early morning ongoing convection across the eastern
and northeastern areas to end by mid to late morning. Warm front
will finally retreat north into the afternoon hours with rather warm
and humid conditions across the area for the remainder of the day.
Some cloud cover extending across the northeast with light showers
then will give way to some sun in the afternoon. As has been
advertised...highs will warm into the upper 80s to lower 90s over
the south with the upper 70s in the far north by late day Friday. No
rainfall is expected until the long wave trough approaches Saturday
morning with showers and thunderstorms moving into Central Iowa by
mid to late afternoon. Remnant tropical moisture from Paine will
probably still be available at this time across our area. With a
ribbon of higher precipitable water and decent convergence along the
boundary...will likely see a decent rain event with up to an inch
additional from Saturday evening through Sunday. Once this feature
pulls east...the models are in some consensus for next week. Both
the Euro and GFS now suggest that the H500 long wave trough will
keep the moisture channel south and east of the region. This should
allow for a period of little to no precipitation and help the river
situation across the area. Temperatures next week look cooler and
more seasonal for the first week of fall.
&&
.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 700 PM CDT Thu Sep 22 2016
Additional thunderstorms and showers expected to develop by late
evening into the overnight hours. Expect main impacts to be at
KFOD and possibly KALO, KMCW, and KDSM as the activity spreads
across the state overnight. Potential for continued development
near the KFOD area into early Friday, thus highlighted for now
with a VCSH. As trends become more apparent, will fine tune the
mentions. CIGS MVFR to low VFR overnight and may have some IFR
across KFOD.
&&
.HYDROLOGY...
Issued at 307 PM CDT Thu Sep 22 2016
Magnitude and placement of the heavy rains will be key tonight. As
mentioned above the environment is not as favorable as last night
but still supports heave rain. The surface based potential is trying
to recover with uncapped 1500-2500 j/kg MLCAPEs now in place over SW
IA. This recovery may be too late to get anything going, but will
likely aid slightly elevated convection just to the north and east
tonight. The latest objective analysis pegs 0-2km moisture
convergence along the Highway 20 to 30 corridors so this will be the
favored location, likely anchored along or just south of the current
Waterloo MCS which won`t go away. Precipitable waters are already
around 2 with warm cloud depths higher than yesterday to 4km. Thus
the moisture transport and instability components will not be as
good as yesterday, but efficient rains are still anticipated. This
will result in 1 rainfall amounts through the aforementioned
favored corridor with locally higher amounts from 2-3 possible,
thankfully south of where yesterday`s heavy rain occurred. Storms
will not be fast moving with a mean of only 15-20kts and Corfidi
vectors slow to the south. Thus have kept the flash flood watch in
place through 18z Fri and expanded down to the full Highway 30
corridor from Guthrie County eastward. A small section of west
central IA counties has been canceled however, which does not seem
to be under the gun and didn`t receive much rain overnight.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Friday afternoon for IAZ004>007-
015>017-023>028-034>039-046>050.
&&
$$
SHORT TERM...Small
LONG TERM...REV
AVIATION...Beerends
HYDROLOGY...Small
Area Forecast Discussion
National Weather Service Quad Cities IA IL
901 PM CDT THU SEP 22 2016
.UPDATE...
Issued at 859 PM CDT Thu Sep 22 2016
I have issued a flash flood watch for our Highway 20 counties in
northeast Iowa, where storms are already beginning to train and
move over the same locations repeatedly. With PWAT values around 2
inches overnight, these could easily produce rainfall amounts of 2
to 4 inches, possibly more in locallized areas. The HRRR suggests
storms should continue to be active overnight, possibly through
mid morning, and that will be how long I carry this watch.
&&
.SYNOPSIS...
Issued at 345 PM CDT Thu Sep 22 2016
Remnants of the larger MCS last night in northern IA/southern MN
which dropped 4 to 10 inches of rain continues to fester in the
form of scattered showers and isolated thunderstorms in the dvn
cwa. This is mainly north of Interstate 80 along a CAPE gradient.
Extensive cloud cover was keeping instability in check in the
north with 3 pm temperatures in the lower to mid 70s. More
sunshine in the far south was allowing for temperatures near 90.
Looking to the west, skies were sunny in western and central IA
where the better low level convergence, stronger deep layer shear,
steeper lapse rates and higher CAPES were located. This is where
additional convection should fire later this afternoon. Haase
&&
.SHORT TERM...(This Evening through Friday)
ISSUED AT 345 PM CDT Thu Sep 22 2016
Forecast focus on thunderstorm chances mainly north.
Tonight: CAM`s models indicated thunderstorms to fire across
northern/central IA later this afternoon and evening. These
storms should then push eastward across roughly the northern half
of the dvn cwa this evening and overnight. The ECMWF/GFS is a bit
farther south with the heaviest rain axis compared to the HRRR.
The better coverage of storms should be in eastern IA and northern
IL along and north of Interstate 80 so this is where the highest
pops will be. Some of the storms may produce locally heavy rainfall
of potentially at least an inch or two. Any repeating storms over
the same area may produce several inches of rainfall in a short
time with PWAT`s approaching 2 inches. There is still uncertainty
of where exactly the highest rain amounts will fall tonight with
variance in the models. Later shifts can monitor convective trends
and adjust pops if needed. Minimum temperatures should be in the
mid to upper 60s.
Friday: Scattered thunderstorms are possible over most of the cwa
in the morning then the storms should shift northward as an upper
level ridge/building heights shifts into the area. This will push
the warm front northward into Wisconsin as the day progresses.
Much of the afternoon should be dry except we will still carry a
chance pop in the north. Highs should be in the upper 70s along
Highway 20 to the mid to upper 80s elsewhere. This will again be
a warm and humid day at most locations with dewpoints well into
the 60s. Haase
.LONG TERM...(Friday Night through Thursday)
ISSUED AT 345 PM CDT Thu Sep 22 2016
Friday night and Saturday, an upper ridge will traverse the forecast
area with mainly dry and unseasonably warm conditions. Saturday
night and Sunday, active weather will return with sharp
southwesterly flow aloft and a slow moving cold front oriented
parallel to the upper flow. Precipitable water values are expected
to rise close to 2 inches once again. This scenario will be
favorable for additional heavy rain, especially across eastern Iowa,
which will be crucial regarding river flooding next week. The
potential for severe storms is minimal due to a number of factors,
including timing and relatively weak deep layer shear. RPK
Sunday night...Latest trends(more progressive) on the various medium
range models suggest a post-frontal shower regime laying out mainly
along and east of the MS River Valley, which would ideally be away
from the swollen IA tributary rivers. Both the 12z NAM and ECMWF
mainly have light rainfall amounts of 0.15 inches or less in these
areas, while the 12z GFS is more bullish with post-frontal moisture
stream making for 0.25 to over a half inch of additional rainfall
from the MS RVR on eastward. For now will take a QPF blend and
migrate POPs more toward the east.
Monday and Tuesday...Large model descrepancies start popping up with
the major medium range players the 12z GFS and ECMWF early next
week. The GFS blocks a nearly stacked cyclone acrs far northern MN,
while the new ECMWF is further north and more progressive with the
upper trof migrating the main axis toward James Bay by Monday
evening. Both models are basically dry for Monday for different
reasons, the GFS with the CWA under in-whirling dry slot into the MN
cyclone center, while the Euro starts exiting out broad cyclonic flow
in favor of upstream ridging. Highs mainly in the 60s on Mon.
Model differences really apparent on Tue with The GFS wrapping
around instability showers acrs the northern half of the CWA Tue
afternoon, while the 12z ECMWF maintains dry, in-building ridge
regime and near normal temps in the upper 60s to lower 70s. For now
will have to maintain low/slight CHC POPs with the descrepancies but
at least that is a drier trend. With a cloud clear out, Tue night
lows will be down in the 40s for most of the area.
Wednesday and Thursday...Longer range trends are for an Omega Block
type pattern to set up shop acrs the mid CONUS somewhere, which
would translate to welcome mainly dry weather and seasonable temps
for the mid to late week period. But again, the latest run medium
range models especially the GFS/ECMWF, vary in placement of their
mean axis. The GFS keeps a trapped/blocked cut-off upper low far
enough to the west acrs the western GRT LKS to spiral more showers
back acrs the area Tue night into Wed, while the Euro progresses the
Omega Block axis eastward to the MS RVR Valley basin by late Wed
night and continues a basically dry regime into day 7 of the
forecast. Again with the descrepancies, will keep low POPs for
showers mainly acrs the northeastern to eastern half of the CWA Tue
night and Wed, then dry for Thu. But if additional model runs
continue to progress with the incoming pattern regime, see the drier
ECMWF solutions winning out for mid next week. Temps may generally
be in the 60s to around 70 for highs, and lows in the 40s. Clouds
will make for cooler highs and milder lows in spots if cyclone wrap
around stratocu maintains more or hangs on with higher coverage than
currently expected. ..12..
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 623 PM CDT Thu Sep 22 2016
Showers and thunderstorms will be possible this evening and
overnight, in all areas of eastern Iowa and northwest Illinois.
This will result in a forecast of vicinity showers in all
locations for this evening, but with a more organized round of
storms expected tonight in northern Iowa, I have put in a tempo
group for thunderstorms at DBQ. Some periods of MVFR are possible
in light fog toward sunrise, but otherwise mainly VFR weather is
expected outside of thunderstorms. Winds will be light and
variable except near storms overnight, and should become steady
south to southeast again during the day Friday.
ERVIN
&&
.HYDROLOGY...
Issued at 345 PM CDT Thu Sep 22 2016
Overview: Repeated rounds of very heavy rain have occurred over
northern Iowa, southeastern Minnesota, and western Wisconsin over
the past three days. A widespread 3 to 5 inches of rain has fallen
with isolated amounts of 6 to 9 inches. Additional heavy rainfall
is possible tonight and again Saturday night in the same general
area.
These extreme rainfall amounts will result in significant river
level rises downstream into eastern Iowa, including the
Mississippi River, into next week.
The majority of local river sites are now under either a flood
warning or flood watch as significant rises are forecast to begin
this weekend or early next week.
Warnings:
On the Cedar River, Iowa River, Wapsipinicon River (De Witt 4S),
and Mississippi River (sites Dubuque LD11 and Dubuque)
Confidence...Moderate on river level forecasts. Uncertainty arises
with respect to forecast crests, not on whether river levels will
exceed flood stage. How high rivers rise above moderate or major
flood stage is dependent on the downstream propagation of upstream
runoff. As new data is gathered over the coming days, forecast
confidence will likely increase.
Watches:
on the Mississippi River (all sites except Dubuque LD11 and
Dubuque) and Wapsipinicon River (Independence and Anamosa).
Confidence...Low to Moderate on river level forecasts because
river levels will depend on the amount of runoff that is routed
downstream through several tributary rivers. As new data is gathered
over the coming days, forecast confidence will likely increase.
&&
.DVN Watches/Warnings/Advisories...
IA...Flash Flood Watch through Friday morning for Buchanan-Delaware-
Dubuque.
IL...NONE.
MO...NONE.
&&
$$
UPDATE...Ervin
SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...12/RP Kinney
AVIATION...Ervin
HYDROLOGY...Brooks/Uttech
Area Forecast Discussion
National Weather Service Hastings NE
700 PM CDT THU SEP 22 2016
.UPDATE...
Issued at 649 PM CDT Thu Sep 22 2016
Updated the forecast tonight to expand the area of fog mentioned
tonight to include some areas along and just south of I-80 from
near Kearney and farther west where stratus stuck around longer
today. Am contemplating hitting the fog a bit harder than we have
in the forecast, judging by later HRRR runs.
&&
.SHORT TERM...(This evening through Sunday daytime)
Issued at 417 PM CDT Thu Sep 22 2016
Forecast highlights/overview of these next 72 hours:
The primary concern through these 72 hours centers around the
still-somewhat- unclear rain/thunderstorm chances centered on the
Friday night- Saturday night time frame (rain chances/PoPs have
been held below "likely" 60+ percentages at this time due to
inherent uncertainty in coverage). Assuming that at least
isolated/scattered activity is able to develop during this time
frame, a few strong to severe storms are not out of the question,
especially Saturday afternoon within eastern parts of the CWA.
Turning back to the nearer-term, have left the forecast void of
any mentionable (meaning 15+ percent) shower/storm chances through
tonight, but these chances are not necessarily "zero" either.
There is some concern for at least patchy fog development mainly
within counties along/especially north of I-80 tonight, with a few
higher-res models such as the HRRR suggesting that this fog could
be a bit more widespread/impactful. For now, have not gotten very
aggressive but did at least introduce a mention of "patchy fog
with visibility less than 1 mile" to tonight`s forecast.
Temperature-wise, unlike today, Friday is expected to have a more
uniform temperature regime with well-above normal heat in all
areas. Then, a gradual cool-down should occur over the weekend,
with highs by Sunday actually slightly below normal (and roughly
20 degrees cooler than Friday).
Taking a look at the current scene as of 330 PM (and as outlined
in the "update" discussion earlier this morning)...sky
cover/temperature forecasting has been a bit of an "adventure"
today thanks to a stark division between widespread sun/heat over
southern/eastern counties and a nearly solid deck of low stratus
clouds over many northern/western counties. As expected, the
southern/eastern edges of this low stratus has in fact slowly
retreated/eroded off to the north and west in response to daytime
heating and mixing. Gave a "best shot" at where actual high temps
will end up, but currently it appears a rather big gradient from
low-mid 70s far north/west-central...mid 70s to low 80s in the
central Tri-Cities area...and noticeably hotter upper 80s to low
and even mid-90s in far eastern and southern counties (hottest of
all in our southern-most KS zones). At the surface, the edge of
this stratus is fairly closely tied to the position of a nearly-
stationary front that is draped across the CWA from west-southeast
to east-northeast. Fairly light north/northeast breezes prevail
north of this boundary while southerly breezes prevail to its
south...and a hodge-podge of light/variable in between. In the
mid-upper levels, a period of weak/subtle ridging appears to be in
control of the Central Plains between a departing shortwave over
IA, and a powerful/highly-amplified trough over the western CONUS
featuring a deep closed low centered over NV.
Now looking ahead forecast-wise through these next 6 day/night
forecast periods...
This evening/tonight:
Despite various hints in various models that at least spotty
shower/thunderstorm activity could at least flirt with the fringes
of our CWA (especially northern areas after dark), decided that
the overall coverage of any of this possible activity within our
borders would remain closer to 10 percent than 20 percent, and
thus these chances are below mentionable thresholds (in other
words, the forecast reads as "dry" but please note that chances
are not necessarily zero). Certaintly, the most legitimate
rain/storm chances tonight should focus north of our CWA from
northern NE eastward into IA, where mid level temps are a touch
cooler and where there is better convergence near the nose of a
modest low level jet. At the surface, the aforementioned front
draped across the heart of the CWA will slowly lift northward as
a warm front overnight in response to low pressure deepening to
the west, turning breezes more southerly as it does so. It is
still unclear exactly what the low stratus deck does, as its
northward-retreat is likely to stall out for a time around
nightfall, keeping it stubbornly over our northern/west-central
zones well into the night before eventually vacating our CWA for
good. As mentioned in the opening paragraph, there are hints of
fog development overnight mainly in counties north of the I-80
corridor, and have introduced a generic "patchy with visibility
less than one mile" to get the ball rolling this direction. Temp-
wise, if anything nudged down lows very slightly, aiming for mid-
upper 60s most areas but low 60s far north.
Friday daytime/night:
This is "part 1" of our upcoming rain/storm chances, and
confidence is pretty high that they will not even arrive in
western zones until after dark. In the mid-upper levels, the
aforementioned deep western trough will gradually approach/invade
the Central Plains, with its primary mid level vort max reaching
western WY by late afternoon, and into southeast MT by daybreak
Saturday. Ahead of this system, confidence remains rather high in
a dry, mostly sunny and very warm (some would say hot) day with
noticeably breezy southerly winds overtaking the entire CWA as the
warm front blasts well to our north. Made little change to high
temps/winds, as the entire CWA is expected to top out 88-91 in the
presence of sustained south winds 15-25 MPH and gusts 25-25 MPH,
highest in the afternoon. Then, as the night wears on, forcing
gradually increases from the west, and fairly low chances for
isolated to perhaps scattered of showers/thunderstorms arrive to
the western CWA before midnight and then expand CWA-wide late in
the night. Can`t completely rule out a rogue strong to marginally
severe storm mainly with hail, but this should be the exception.
The invading north-south oriented synoptic cold front may be right
on our western doorstep by night`s end, but ahead of this boundary
low temps should hold up mid-upper 60s most areas.
Saturday daytime/night:
This is "part 2" of the storm chances, but confidence in areal
coverage of this rainfall is still not high enough to justify
"likely" PoPs within the CWA. Certainly though, chances are higher
in southern/eastern counties than they are in northern/western
counties (which could really end up missing out on things). In the
mid-upper levels, the main vort max swings north toward ND during
this time, while the large-scale trough trailing to its south
slowly edges east through the Plains. Meanwhile at the surface,
barring some fairly big changes, models have seemingly settled on
a steady west-to-east progression of the synoptic cold front
through the CWA during this time. Based on instability/shear progs
and the timing of the boundary, especially our eastern-most
counties may see at least a brief severe storm threat Saturday
afternoon along this front, and agree with the SPC putting these
areas in a Marginal Risk. This will bear watching, because if the
front slows at all, then more of our CWA may be in a severe risk
mainly for large hail/wind. Taking the latest models literally
(especially the NAM) suggest that the majority of shower/storm
chances may be over with by sunset. However, models such as the
ECMWF/GFS are slower with precip departure, and thus will linger
modest PoPS through the night especially in eastern/southern
zones. High temps are aimed low 80s most areas and with With
cooler air invading, lows expected to drop into the 50s nearly all
areas.
Sunday daytime:
Although it could be a close call in extreme southeast zones,
confidence was high enough to leave the entire CWA void of
shower/storm chances behind the departing cold front. As a result,
we are looking at a "fallish" day featuring plenty of sunshine,
cooler temps and breezy northwest winds averaging 15-20 MPH with
higher gusts. If anything, nudged up highs 1-2 degrees given
expectation of sun/decent mixing, aiming for 69-72 most areas.
.LONG TERM...(Sunday night through Thursday)
Issued at 417 PM CDT Thu Sep 22 2016
Fall-like conditions are forecast to continue on into the beginning
of the next work week, with temps climbing back to normal by mid-
week.
The main change made to the forecast for the long term was to remove
precipitation chances. At the start of the period, models are in
pretty good agreement showing the main upper level trough axis
continuing to push through/east of the CWA. By 12z Monday, the axis
looks to extend from central MN south through central KS, with
northwesterly winds in place across the CWA. That northwesterly flow
aloft remains in place through at least Mon/Tues, as ridging over
off the west coast starts pushing east through the Rockies. As we
get into Wed/Thurs, that ridging moves onto the Plains/right over
the CWA. The 12Z run of the ECMWF/GFS are in good agreement showing
little in the way of disturbances moving through, keeping this dry.
The 12Z run of the Canadian is an outlier, keeping a massive cut off
lower pressure system over the central CONUS through the period.
At the surface, high pressure builds into the region behind the
weekend frontal passage, with light, northerly winds on Monday
turning more variable for Tuesday. Return southerly flow looks to
return for mid-week. As far as temperatures go, not expecting a lot
of change for Mon/Tues compared to Sun, with highs generally in the
mid-upper 60s and dewpoints in the 30s and 40s. Warmer temps
forecast for mid-week with the upper ridge building in, reaching the
mid 70s by Thursday.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday evening)
Issued at 649 PM CDT Thu Sep 22 2016
Biggest issue will be low-level wind shear overnight as a low-
level jet develops. We will be on the northern edge of concern.
Also, visibility may lower as we were on the southern edge of
where stratus stuck around for much of the day, so confidence is
really not high here.
&&
.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&
$$
UPDATE...Heinlein
SHORT TERM...Pfannkuch
LONG TERM...ADP
AVIATION...Heinlein
Area Forecast Discussion
National Weather Service Green Bay WI
1001 PM CDT THU SEP 22 2016
Updated aviation portion for 06Z TAF issuance
.SYNOPSIS...
Issued at 223 PM CDT Thu Sep 22 2016
A break in the excessively wet weather, but temperatures remaining
near or above seasonal normals.
Currently on the large scale, strong Pacific jet splits near the
West Coast before merging back together in the Great Lakes region.
The pattern will be slowly progressive, especially early in the
forecast period. Ridging building northeast from the eastern
Pacific will force the location of the split eastward into the
Plains by the weekend. Thereafter, the evolution of the flow
regime becomes uncertain as the medium range models offer varying
ideas on the handling of the remnants of the current southern
stream upper trough. That uncertainty will impact precipitation
chances during the latter part of the forecast period.
Temperatures are expected to remain near to modestly above
seasonal normals through most of the the period, though they could
tail off late. Shower chances will continue the next couple days,
especially across the southern part of the forecast area. But
rainfall amounts should remain on the light side. Precipitation
chances during the middle to latter part of the period will depend
on the evolution of the current southern stream upper trough now
over the western CONUS, and thus are a low-confidence aspect of
the forecast. The best estimate is that rainfall totals for the
next 7 days will end up AOA normal, though at this point amounts
do not look excessive.
&&
.SHORT TERM...Tonight and Friday
Issued at 223 PM CDT Thu Sep 22 2016
The latest RAP analysis and satellite/radar imagery show a nearly
stationary surface cold front stretching from west-central WI to
near Wausaukee early this afternoon. Scattered morning showers died
off along the boundary by midday, but the hi-res models continue to
indicate that a few showers will be possible over east-central and
far northeast WI and within a pwat axis through the rest of the
afternoon. Not convinced that will occur since there is little to no
instability, but left a small chance just in case. Observations
also indicate the presence of some drizzle over far northwest
Wisconsin within a band of low clouds behind the front. Some of
this drizzle could move into Vilas county later this afternoon. As
the front finally makes a move southward tonight, small precip
chances and cloud cover are the main forecast concerns.
Tonight...The cold front will finally move south across central and
northeast WI this evening, and into southern WI overnight. Position
of the pwat axis and hi-res models indicate that east-central WI
could see a shower or two early in the evening before the front
exits the forecast area. But will leave a slight chance across the
south in case the front is slower to exit than progged. Otherwise,
should see widespread cloudiness linger behind the front per
satellite imagery. A developing northeast breeze should keep the
boundary layer churned up to limit fog potential even after all of
the rainfall. Lows falling to near 50 in the north to near 60 in
the south.
Friday...The cold front will settle over far southwest Wisconsin and
northern Illinois. A band of low clouds are expected to remain
behind the front, which should keep central and east-central WI more
cloudy than over northern WI, where northeast winds will push in
drier air. Cannot rule out a few showers over central and east-
central WI in a region of modest mid-level fgen. Because of more
sunshine, northern WI could be as warm or warmer than locations
further south. Will go with highs mostly in the mid 60s.
.LONG TERM...Friday Night Through Thursday
Issued at 223 PM CDT Thu Sep 22 2016
Weak isentropic lift will begin spreading back across the area
Friday night. That seems worthy of having chance PoPs expand
northeast across most of the area during the night, though with
limited instability opted to leave thunder out of the forecast.
Though confidence in precipitation forecast for the rest of the
period is probably lower than normal, leaned toward the ECMWF for
PoPs. The 12Z EC was fairly consistent with its previous run, and
exhibited decent consistency with the GFS ensemble mean. That
resulted in a prolonged period of chance PoPs as the upper trough
crosses the area. The best chance for rain looks to be Sunday and
Sunday night, though that could easily chance in later forecasts.
No significant changes were necessary to the extended forecast
initialization grids based on a broad blend of guidance products.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 951 PM CDT Thu Sep 22 2016
Late this evening, a surface front is shifting south of Wisconsin
while an 850 front slides southward over the state. A mix of IFR
and MVFR cigs with isolated light showers or sprinkles will be
associated with this 850 front. Patchy fog will also be possible
tonight. Drier air pouring in from the north should improve
northern and Northeast Wisconsin to VFR conditions Friday morning
as high pressure drifts over the northern Great Lakes Region. Cigs
over Central and East Central Wisconsin may improve to lower end
vfr cigs later Friday morning, with scattered showers lifting
back north as the surface front begins to move north again.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS.......Skowronski
SHORT TERM.....MPC
LONG TERM......Skowronski
AVIATION.......TDH
Area Forecast Discussion
National Weather Service Wilmington NC
1050 PM EDT Thu Sep 22 2016
.SYNOPSIS...
Weakening low pressure will drift offshore of the Carolinas
through late Friday, taking the rainfall threat with it.
Weak high pressure accompanied by drier air will prevail on
Saturday. A modest cold front will drop south across the area
early Sunday. Modest high pressure will follow and ridge across
the area from the NE states through the early to mid week period
of next week.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 1015 PM Thursday...Still have active pcpn affecting the
area, and should continue for much of the overnight. The sfc and
upper lows are straddling the coast along Horry and Georgetown
counties, and is trying to make some headway along the coast to
the NC-SC border by daybreak Fri. The activity will transition to
mainly over the adjacent Atlantic Waters and occasionally moving
onshore affecting the coastal counties during the pre-dawn hours
and into daytime Friday. The activity may further increase in
coverage and intensity during daytime Fri due to the availability
of insolation and in turn increased instability. Will continue to
highlight the HWO with possible flooding and ponding across
vulnerable locations, especially areas that have received a
plethora of rainfall during the past 12 to 24 hrs. Minor tweaking
applied to overnight temps/dewpts due to pcpn occurrence. No
changes to the Min temp fcst
Previous.................................................
As of 600 PM Thursday...POPs have been increased thruout this
evening with the going concern being the continued moderate to
heavy rain being produced by the convection. Lightning data has
been limited/sparse across the Carolinas and therefore will just
mention isolated thunder thru mid-evening. With the moderate to
heavy rain persisting well into this evening, unlike what the
latest HRRR and RAP indicate, have updated the pcpn phraseology to
include "heavy rain". In addition, with a half a dozen of Flood
Advisories issued, have updated the Hazardous Weather Outlook to
include the potential for temporary ponding or shallow flooding
from this evenings local heavy rains.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Low pressure over the Cape Fear area will
weaken and move east through Friday as high pressure builds down
from the north. The main mid to upper trough will lift off to the
north and east and a ridge builds over the southeast, although both
the ECMWF and the GFS show a low cutting off from the main trough
and lingering across the deep south into Sun. A weak backdoor
front will make its way south through VA and into NC Sat night and
should reach into SC by Sun morning. Pcp water values up close to
1.9 inches on Fri mainly aligned along the SC/NC coast will
diminish to less than 1.5 inches by Sat aftn with drier air and
subsidence finally scouring out the remaining moisture from this
persistent remnant low from Julia. Therefore, will continue with
higher pops and greatest chc of shwrs/tstms on Fri mainly east of
I-95 to the coast as sfc low remains just off the tip of Cape
Fear. Expect clearing to occur through late Fri into Sat as Dry
air and subsidence work there way south and east as upper ridge
builds east through Saturday. This should produce plenty of
sunshine across much of the area, but lingering moisture along the
coast should produce some cu and possibly some isolated showers
mainly over the SC coast Sat aftn. Not expecting much change in
the feel of the air mass with humid weather continuing. Clouds
will be tough to break on Fri with continued showers and therefore
expect high to be in the 70s much of the day, but places that
break out in the afternoon should reach into the 80s. Saturday will
warm well into the 80s with a good deal of sunshine across much of
the area. Overnight lows will be in the mid 60s to around 70.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 300 AM Thursday...A mid-and-upper level ridge axis will
shift from the TN valley Sunday to the east coast by Tuesday, and
will amplify between two anomalously strong upper lows into a
Omega block-type pattern. At the surface, high pressure will
ridge down across the mid-Atlantic states and produce onshore
flow through the period. Although the primary belts of deepest
moisture will remain south and west of the area, persistent
onshore flow below 850 mb would provide sufficient moisture to
support scattered showers.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
As of 00Z...Periods of MVFR possible tonight as scattered
showers and thunderstorms move across the area. MVFR/IFR
anticipated late overnight into early Friday morning due to areas
of low cigs and patchy fog. After daybreak, conditions are
expected to improve to VFR with isolated to scattered showers.
Light east-northeasterly winds will persist through the valid TAF
period.
EXTENDED OUTLOOK...Isolated to scattered convection, mainly
during the afternoon and evening hours is possible beneath the
cutoff upper low through Friday. MVFR/IFR morning stratus/fog
possible each day through Saturday. Expect mainly VFR Sunday
through Tuesday.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 1015 PM Thursday...This update mainly concerned with pcpn
coverage during the pre-dawn Fri hours. The sfc and upper lows are
situated along the NE South Carolina coast, and is slowly making
some headway to the NE...and should reach the NC-SC border by
daybreak Fri. Some very minor tweaks to wind direction applied due
to the slower movement. In addition, the wrapping affect around
the sfc low will continue overnight. Could see a few streamers
ahead of the low, ie. Moving northward along Cape Fear and also
onshore in the vicinity of Surf City or further northward along
the coast into MHX CWA. Significant seas remain a solid 2 to 3 ft
with majority coming from the ese ground swell at 11-13 second
periods from distant Karl.
Previous......................................................
As of 600 PM Thursday...A relatively relaxed sfc pg will yield 10
kt or less wind speeds tonight. The progged sfc pressure field
itself paints the elongated sfc low, underneath the upper low,
straddling the coasts of NC and SC thru tonight. Could go variable
in direction especially with speeds only at 5 to 10 kt, but
instead will identify the more predominate directions, southeast
to south. Significant seas will primarily be driven by a 1.5 to
2.5 foot, e to ese ground swell from distant Tropical Cyclone
Karl. Latest Spectral Density Chart for 41013 indicates the ese
11-13 second period Karl swell is definitely driving the
significant seas.
Have increased the convection coverage this evening based on
latest KLTX 88D trends. In addition, have highlighted the
persistent convection over the northern-most waters oriented
parallel to Cape Fear, as it pushes northward and onshore.
Waterspout(s) has/have been sighted earlier today in the vicinity
of this pcpn. Will mention this waterspout risk until sunset in
the Hazardous Weather Outlook.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Low pressure just off the tip of Cape
Fear will finally move away as high pressure builds down behind
through Saturday. A cold front will drop south reaching NC Sat
night and should move through the waters by Sun morning. This may
be fairly transparent as winds will have already shifted to the
N-NE by late Fri as low weakens and shifts east. Therefore light
and variable winds on Fri will become northerly by early Sat and
will remain N to NE through Sat night increasing up to 15 kts.
Seas 3 ft or less will increase up to 2 to 4 ft into Sat night. A
longer period SE-E swell will continue through the weekend, up to
11 to 12 seconds.
LONG TERM /SUNDAY THROUGH MONDAY/...
As of 300 AM Thursday...Surface high pressure will build down the
eastern seaboard behind a cold front, which should be crossing
the waters during the day Sunday. With a blocked upper-level
pattern developing through the first of the week, the surface high
will persist and result in onshore flow through Monday. It does
still appear that 3-4 foot swells every 10 seconds will continue
into Sunday from distant tropical system Karl, falling off to a
2-3 foot wind wave by Monday.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.
&&
$$
SYNOPSIS...DCH
NEAR TERM...DCH
SHORT TERM...RGZ
LONG TERM...RGZ
AVIATION...SGL
Area Forecast Discussion
National Weather Service Phoenix AZ
900 PM MST THU SEP 22 2016
.SYNOPSIS...
Drier air and slightly cooler temperatures will be over the area for
the remainder of the week. Breezy, but otherwise quiet weather will
be the rule for the weekend and into early next week along with a
warming trend.
&&
.DISCUSSION...
After an interesting afternoon in the Phoenix area with some fast-
moving dynamic thunderstorm activity we are seeing things quieting
down a lot. Humidity is still present with dew points in the high 60s
and low 70s in the Phoenix area but have substantially dried out to
the west, going into the 20s and 30s in the Imperial Valley and
Colorado River valley. Some gusty winds are present and have led to
some areas of blowing dust in southeast California. That activity
should be diminishing this evening. The next few days should be
relatively quiet with cooler dry air settling in over the region.
Temperatures should stay below normal levels.
By Sunday a cutoff low pressure system is forecast to cut off over
southern NM. This will keep us in relatively cool northerly flow. One
curiosity in the long range is yet another tropical system that at
least one model (GFS) is bringing back up into the Baja/AZ area in a
very similar track to Paine. That`s a pretty unusual track for very
late in September but not out of the question. For now it`s just
something to watch and see. A lot can happen in the next week.
&&
.PREVIOUS DISCUSSION...
Initial line of showers steadily dissipated as it tracked eastward
across the Phoenix area early this afternoon. In its wake, more
scattered but organized storms have developed across portions of
western Maricopa County within a moist and unstable environment with
dewpoints as high as the lower 70s yielding MLCAPEs exceeding 1000
J/kg. Meanwhile, NAEFS percentiles show a widespread area of
anomalous PWATs, exceeding the 90th percentile across central AZ
extending northward.
Latest runs of the HRRR continue to have a good handle on the
situation and indicate that additional activity will develop this
afternoon before dissipating around 5pm. The strongest storms are
expected generally to the north and west, where temperatures aloft
are cooler and in the vicinity of the strongest deep-layer shear
associated with the closed low across central California. Main
threats include brief heavy rain, strong winds gusts and small hail. Otherwise,
PoPs remain in the forecast overnight for southern Gila County.
Global models continue to suggest strong vorticity-forced ascent
ahead of the trough axis will tap into some residual moisture to
generate scattered showers in these areas.
&&
.PREVIOUS DISCUSSION...
Gusty west winds are expected to develop over the western deserts
this afternoon behind the front, with the strongest winds likely to
occur over favored areas of Imperial county; peak gusts to 35 mph
are likely. There may be some patchy blowing dust occurring due to
the wind, but recent rains in the area will limit the potential for
any significant dust and as such we will not mention blowing dust in
our forecast grids at this time. As far as temperatures go today,
with thickness values lowering to around 576dm and with considerable
lower clouds and showers in the area, high temperatures will fall to
well below seasonal normal values with many lower AZ deserts falling
into the upper 80s to low 90s. Phoenix should see a high around 90
today which would be 8 degrees below normal.
On Friday, the main upper low is forecast to quickly lift off to the
northeast but a much drier and more subsident northwest flow aloft
will overspread the deserts. Outside of a lingering slight chance of
showers over southern Gila County we can expect generally sunny skies
over the lower deserts with continued below seasonal normal high
temperatures. PWAT values are forecast to fall to around one quarter
of inch over much of the lower central deserts by Friday afternoon
and the surface dewpoints in the Phoenix area will fall from the mid
to upper 60s today into the upper teens to mid 20s.
Over the weekend and into next week, dry conditions are forecast
area wide with no threat of precipitation. A large upper ridge will
initially amplify along the west coast giving a dry northerly flow
to the area but early next week the ridge will flatten somewhat but
continue giving dry northwest flow into the lower deserts. Expect
generally sunny days and clear nights this weekend into the middle
portion of next week along with a gradually warming trend. High
temperatures will climb into the mid to upper 90s over most of the
lower deserts by the early to middle part of next week.
.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:
Shower and thunderstorms continue to develop upstream of the Phoenix
area terminals and all terminals stand a chance to see some precip
activity through the evening hours. Airfield vsbys may take a sudden
drop under the heaviest shower activity and resulting winds will
also be on the rather variable and erratic side. Otherwise, CIGs
will linger 3-5kft into the evening before transitioning eastward
with FEW to SCT clouds lingering after sunset. Any continuing shower
activity should move and stay east of the terminals for the
overnight hours.
Southeast California/Southwest Arizona including KIPL and KBLH:
Breezy to windy conditions to persist for KIPL and KBLH as a cold
front continues to pass through the region. Gusts 25 to 30kts will
linger into the overnight, with sustained winds holding in the 10 to
15kt range. Skies will remain mostly clear with any shower activity
remaining well to the east of the River and the terminals.
Aviation Discussion not updated for amended TAFs.
&&
.FIRE WEATHER...
Saturday through Wednesday...
Very dry northwesterly flow aloft behind a trough to the east on
Saturday will eventually be replaced by a dry ridge of high pressure
on Wednesday along with below normal high temperatures throughout
the period. Breezy to occasionally windy northerly component winds
will prevail out west, especially along the lower Colorado river
valley each afternoon through Monday with gusts of 20 to 28 mph,
although conditions are not expected to reach critical thresholds
at this time. Gusty northeasterly winds will then spread into the
lower deserts and the higher terrain of southern Gila county
beginning Tuesday. Minimum RH of 13 to 20 percent on Saturday will
slowly increase each day until reaching only 20 to 30 percent on
Wednesday. Fair overnight recoveries on Saturday will improve to
fair to good by Tuesday.
&&
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected through Sunday.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
Visit us on Facebook...Twitter...and at weather.gov/phoenix
DISCUSSION...Waters/Hirsch
PREVIOUS DISCUSSION...CB
AVIATION...Nolte
FIRE WEATHER...Sawtelle
Area Forecast Discussion
National Weather Service Las Vegas NV
826 PM PDT THU SEP 22 2016
.SYNOPSIS...Strong and gusty winds across San Bernardino County
will diminish overnight as a strong area of low pressure moves east
into Utah and Arizona. Scattered showers and thunderstorms over
northern Mohave County will also come to an end. Below average
temperatures are expected through the weekend, warming to near
average early next week, with drier and calmer conditions
anticipated.
&&
.UPDATE...Wind speeds have diminished on schedule so let most of the
products expire as scheduled. Did downgrade the High Wind Warning
for the western Mojave Desert to a Wind Advisory and left the
advisory up for the Morongo Basin as well.
Heavy rain threat has ended for northern Mohave County so went ahead
and cancelled the Flash Flood Watch a few hours early.
Strong winds throughout the day lofted quite a bit of dust into the
air. Visibilities locally being impacted by this suspended dust now
so added a large swatch of haze to the high desert of San Bernardino
County, Clark County and western Mohave County. Would expect the
visibilities to gradually improve overnight and Friday as the dust
settles out.
&&
.AVIATION...For McCarran...Forecast confidence is low on
the exact influence of a cold front this evening. Some forecast
computer models are suggesting winds will struggle to become
northwesterly and settle in a more westerly direction while others
push through the front and bring northwest wind overnight. For now,
the TAF will hint at a slight WNW direction overnight with a more
gradual shift to NW overnight as winds subside. Mechanical
turbulence and low level wind shear impacts will diminish overnight
as winds subside.
For the rest of southern Nevada...northwest Arizona...and southeast
California...Chances of showers/storms confined to Mohave and
Lincoln Counties today with strong west to southwest winds the main
concern elsewhere. Cold front will move through the southern Great
Basin and Inyo County this afternoon/evening with switchover to
northwest directions during/after passage. Winds should diminish
after sunset, but may be slower to occur in the Mojave Desert. VFR
conditions outside of storms. Mechanical turbulence and mountain
wave activity is anticipated through this evening.
&&
.PREV UPDATE...554 PM PDT THU SEP 22 2016
.UPDATE...Increased POPs back westward into northeast Clark
County/eastern Lake Mead National Recreation Area as new line of
storms has developed from Temple Bar area northeast through
Mesquite. A line of stronger storms continues to exist from north of
Kingman to Colorado City. HRRR simulations have been consistent
showing lines of convection weakening or moving out of Mohave County
around 9 pm. Cold front making progress southeast and currently lies
from Alamo-Desert Rock-Ridgecrest. Frontal passage for Las Vegas
still looks to be around 8 pm. &&
.PREV DISCUSSION...242 PM PDT THU SEP 22 2016
.SHORT TERM...through tonight.
WV imagery showing deep trough/upper low continuing to dig
southeastward into the Great Basin this afternoon. Jet streak is
approaching the base of the trough, with substantial
difluence/divergence in eastern Nevada, Utah, and northern Arizona
in favorable left front quadrant region. Substantial large-scale
lift from differential cyclonic vorticity advection has reached the
more unstable warm sector of far eastern Nevada SSE to western
Arizona, and more intense updrafts have recently developed in
Lincoln County southward to Lake Mead. High-resolution guidance is
consistently showing a band or bands of storms developing in this
general area moving eastward into southwest Utah and northern Mohave
County over the next several hours. Environmental parameters remain
favorable for storm organization, with effective bulk shear 30-40
kts and MUCAPE 500-1000 J/kg sufficient for isolated severe storms
capable of producing damaging wind gusts. Though potential for hail
exists, think the general weakness of the updrafts will not support
a more widespread threat. Storm motions will be fast with such
midlevel steering winds in place, but if sustained updrafts can
develop in small bands or lines, training thunderstorms with
efficient rain rates will be capable of producing localized flash
flooding, especially with antecedent rains in northern Mohave County
the last couple of days. Flash flood watch remains in effect for
this area this evening.
Winds look to remain strong as the trough axis approaches the area
this evening, but a cold front sweeping through the southern Great
Basin at this time will generate a switchover to northwest winds
with speeds decreasing rapidly thereafter. Dust has been kicked up
across the Mojave Desert this afternoon, with reduced visibilities
reported along I-15 from Baker to Barstow. Expect blowing dust to
remain a concern through sunset in this region before gradual
improvement with lowered wind speeds thereafter. Current wind/dust
products look good and did not change with the afternoon package.
Red flag conditions are being met across much of the area this
afternoon as well. See the fire weather discussion for more
information.
Sharply cooler temperatures are expected tonight as colder air
behind the front seeps into the region. Expect temps anywhere from 7-
15 degrees colder than those observed last night.
.LONG TERM...Friday through Thursday.
A final shortwave over southern Nevada will be moving through the
base of the vigorous trough early Friday morning. This will allow
the upper trough to start moving eastward into the Four Corner
States by late Friday afternoon. On backside of trough, temperatures
will be much cooler Friday (around 10 degrees below normal) along
with lingering north breezes.
Over the weekend, southern extent of upper trough stalls over the
southern Rockies as strong high pressure begins to build in across
California/western Nevada. Daytime temperatures quickly rebound back
to near normal Sunday. A developing north/south surface pressure
gradient will help enhance north/northeast surface winds, especially
within the Colorado River Valley south of Hoover Dam both days.
More uncertainty next week as models continue to struggle with
handling of southern stream energy pinching off over New Mexico.
Quite a bit of flip-flopping between operational ECMWF/GFS runs as
just last night`s solutions had back away from any energy
retrograding westward across Arizona/northwest Mexico. Based on the
strength of the ridge over California and the Great Basin, it is
plausible. For now, keeping the area dry with temperatures hovering
around normal.
&&
.AVIATION...For McCarran...Southwest winds 20-30 kts with gusts to
40 kts will be likely through the afternoon. Forecast confidence is
low on the exact influence of a cold front later this afternoon on
winds at McCarran. Some forecast computer models are suggesting
winds will struggle to become northwesterly and settle in a more
westerly direction while others push through the front and bring
northwest wind overnight. For now, the TAF will hint at a slight NW
direction at 03z with a more gradual shift to NW overnight as winds
subside. A plausible alternative to the official forecast is that we
will see a sudden shift to the NW (~330) with strong gusty winds at
around 03z. This should be considered in any planning during this
period of time. Mechanical turbulence and low level wind shear will
also remain a problem for the rest of the afternoon.
For the rest of southern Nevada...northwest Arizona...and southeast
California...Chances of showers/storms confined to Mohave and
Lincoln Counties today with strong west to southwest winds the main
concern elsewhere. Cold front will move through the southern Great
Basin and Inyo County this afternoon/evening with switchover to
northwest directions during/after passage. Winds should diminish
after sunset, but may be slower to occur in the Mojave Desert. VFR
conditions outside of storms. Mechanical turbulence and mountain
wave activity is anticipated through this evening.
&&
.FIRE WEATHER...Much drier air has arrived with relative
humidity values plummeting into the single digits along with strong
southwest to west winds. Winds will start to weaken by late evening
as relative humidity values recover above 15 percent overnight as
temperatures cool. North to northeast breezes will continue at times
Friday through Sunday as high pressure builds in across California
and the Great Basin. Temperatures will be well below Friday but will
warm through the weekend.
&&
.SPOTTER INFORMATION STATEMENT...Spotters in northwest Arizona are
encouraged to report severe weather or flooding. Spotters elsewhere
can report significant weather (especially blowing dust, wind
damage, or fire starts) according to standard operating procedures.
&&
$$
Update...Pierce
Short Term:Shafer
Long Term/Fire Weather:Pierce
Aviation: Lericos
For more forecast information...see us on our webpage:
http://weather.gov/lasvegas or follow us on Facebook and Twitter
Area Forecast Discussion
National Weather Service Cheyenne WY
326 AM MDT FRI SEP 23 2016
.SHORT TERM...(Today through Saturday)
Issued at 310 AM MDT Fri Sep 23 2016
Widespread low clouds continue across areas along and east of the
Laramie Range. WYDOT obs from Cheyenne to the I-80 summit show vis
remaining mostly below a quarter mile so the dense fog advisory is
working out well. Will keep it going for central Laramie county
even though the fog has not developed at CYS yet. HRRR guidance
shows much quicker clearing through the morning compared to
yesterday. Models show the closed upper low currently near Salt
Lake City lifting northward into central WY by this evening. The
warm front will lift northward across the plains through the day
with southerly winds strengthening from I-25 eastward. Did
increase wind speeds over the Panhandle with the southern
Panhandle getting close to advisory level (fcst gusts to 35 kts)
by the late aftn.
Cold front is progged to be near the Laramie Range by the aftn,
and this will be focus for shower/tstm development. Went with
40-60 POPs over much of the plains of southeast WY during the aftn
as the HRRR/NCAR ensembles are in good agreement with the global
models. There will be a marginal risk of svr storms across the
plains and especially north of the warm front. This is due to CAPE
values of 500-1000 J/kg and excellent bulk shear. Storm activity
over the plains should begin to die down by the late evening with
the cold front pushing across the Panhandle by 06Z.
The other story with this storm system will be the orographic snow
over the Sierra Madre and Snowy Ranges by late tonight into
Saturday morning. Wet bulb zero heights are around 8500 ft MSL.
Moist westerly 700-500 mb flow on the backside of the upper low
will create favorable orographics, especially over the Sierra
Madre Range. Currently have 1-4 inches of snow over much of the
western mtns, which would be welcome news for the fires that have
been ongoing near the Sierra Madre Range. It will be breezy to
windy on Saturday with highs struggling to get above the mid 60s.
.LONG TERM...(Saturday night through Thursday)
Issued at 310 AM MDT Fri Sep 23 2016
Upper trough moves through the area Saturday night into Sunday.
Going to be cold as 700mb temperatures fall to -4C Sunday into
Monday.
Warmer and drier weather for the rest of the upcoming week as
ridge of high pressure builds back over the area.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1105 PM MDT Thu Sep 22 2016
Challenging forecast for the overnight hours. HRRR guidance
showing IFR/LIFR lifting across the southern Panhandle early this
morning as a trough of low pressure moves out of northeast
Colorado. Generally followed the HRRR guidance on timing/clearing
of stratus and fog. Strong winds this afternoon and evening as a
cold front moves through the area. Could see gusts to 45kts out at
KSNY, KAIA and KBFF, first from the southwest and then from the
northwest when the front moves through.
&&
.FIRE WEATHER...
Issued at 310 AM MDT Fri Sep 23 2016
No fire weather concerns through the weekend. Temperatures will
cool across the entire area after today behind a cold front. Minimum
afternoon humidity values will mostly be above 25 percent through
the weekend. There will be a chance of showers and thunderstorms
through tonight across the region. A few inches of snow will be
possible tonight through Saturday morning over the Sierra Madre and
Snowy Ranges.
&&
.CYS Watches/Warnings/Advisories...
WY...Dense Fog Advisory until 7 AM MDT this morning for WYZ116>118.
NE...None.
&&
$$
SHORT TERM...ZF
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...ZF
Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST THU SEP 22 2016
.SYNOPSIS...A strong low pressure system moving north of the area
will bring a chance of showers and/or thunderstorms, cooler
temperatures and gusty winds at times through Friday. Mostly dry
conditions will then prevail this weekend and into the latter part
of next week.
&&
.DISCUSSION...Showers and a few thunderstorms associated with the
tail end of a low pressure system passing through the Great Basin
had dissipated late this evening. Latest HRRR solution continued to
suggest the possibility of a flare up in showers late tonight and
more so Friday afternoon mainly northeast of Tucson. The current
forecast resembled this solution which still looked plausible. Thus,
no updates anticipated this evening. Please refer to the additional
sections for more details.
&&
.AVIATION...Valid through 24/06Z.
A few showers and/or thunderstorms will continue mainly from the
Tucson area north and westward as a cold front slowly moves through
the area into Friday. Expect a band of SCT-BKN clouds at 3-7 ft AGL
to gradually make its way across the region from west to east as
well. Surface wind becoming terrain driven less than 10 kts
overnight. Breezy westerly to southwesterly winds are expected again
Friday afternoon.
&&
.FIRE WEATHER...Isolated showers and storms are possible through
tonight and again on Friday, especially from Tucson north and
westward as a cold front moves across the area. Southwest winds of
10-15 mph and occasional 20 mph gusts will subside this evening. A
few west to southwest breezes on Friday will continue for eastern
areas. Otherwise, mainly light winds this weekend before increased
easterly breezes move in for much of next week. Minimum relative
humidity values will begin to lower considerably as early as Friday
for far western areas, then for the remainder of the region this
weekend into early next week.
&&
.PREV DISCUSSION...A low pressure system was moving through the
Great Basin region this evening. A small threat for showers will
linger through Friday before the system moves generally over the
northern Rockies with the tail end of the system into the four
corners region by late Friday. As this system swings through, the
associated cold front will result in a significant decrease in
temperatures with highs only expected to be in the mid to upper 80s
for Tucson during the entire forecast period.
The trough axis associated with the aforementioned low pressure
system will linger just to our east into the weekend before an
upstream vort max dives south on the back side of the trough across
eastern Utah and Arizona Saturday into Sunday. As this occurs,
models are showing some significant differences beyond Sunday. The
ECMWF wants to develop a cut-off low over the general vicinity of
southeast Arizona, southwest New Mexico, northeast Sonora and
northwest Chihuahua on Sunday, while the GFS just keeps the trough
to our east over northeast New Mexico through west Texas and
northern Chihuahua. By late Monday the Euro indicates the low will
retrograde over northern Sonora, while the GFS has the tail end of
the trough sliding farther south into north central Mexico.
Meanwhile, the models develop a tropical system near the equatorial
Pacific and the GFS eventually takes it to the north and it becomes
absorbed into the low over southern Baja by the middle to latter
part of next week and moves this whole system northward. On the
other hand, the Euro takes the low over Sonora and moves it
northwest to a position over western Arizona by mid week, but then
kicks it east in response to an upstream trough. The bottom line is
that during the early to latter part of next week, the Euro starts
out wet and then becomes dry, whereas the GFS starts the week out
dry and then ends it wet. So, with this much uncertainty I just have
single digit to slight chance type POPs in the grids/forecast until
models can come to some consensus.
For Tucson, high temperatures will be 8 to 10 degs below normal
Friday, then will range from 3 to 6 degs below normal each day
thereafter, although the coolest days will be Saturday through
Tuesday. Low temps will be near normal Friday morning, then 6 to 8
degs below normal this weekend and within a degree or two of normal
thereafter.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Area Forecast Discussion
National Weather Service Bismarck ND
1001 AM CDT Fri Sep 23 2016
.UPDATE...
Issued at 950 AM CDT Fri Sep 23 2016
The biggest change with this update is associated with the
expansion of the SPC Day 1 Marginal Risk into a great portion of
southwest North Dakota with their 13 UTC outlook. The 11-14 UTC
HRRR iterations and the experimental ESRL HRRR within their 2-5km
updraft helicity forecasts have consistently shown tracks of
75-100+ m2/s2 across southwest North Dakota this evening,
pointing to the potential for organized convection. This is
plausible given increasing low level warm air advection and
moisture transport arching into the southwest north of the
surface low that will be propagating into western South Dakota
and Nebraska, coincident with the next surge of upper level
forcing. 850mb CAPE values around 1000 j/kg in a highly sheared
environment suggest low topped supercells could be possible. Large
hail is the most likely threat given the likely elevated nature of
the storms.
UPDATE Issued at 632 AM CDT Fri Sep 23 2016
For this update, no major changes were needed. Tweaked the
temperatures through the morning hours as well as the QPF
forecast. Otherwise, just blended the most current observations to
the inherited forecast. Decided to keep precipitation chances as is
for the time being, as showers should continue to become more
numerous over western and central North Dakota through the morning
and afternoon hours. Once the surface low begins to mature over
South Dakota, should have a better idea of eventual coverage by
later this afternoon. Isolated thunder is still expected with the
activity today, mainly in the south. Severe weather is not
expected at this time. Stronger shortwave approaches tonight,
bringing more widespread rain and thunderstorm potential to the
west as the low lifts into North Dakota.
&&
.SHORT TERM...(Today through Saturday)
Issued at 515 AM CDT Fri Sep 23 2016
This Friday morning the mid level low, that began impacting our
weather with an increase in clouds yesterday, was over Utah and
progged to move northeast. This is consistent model to model. By
Saturday afternoon it is either over eastern Montana or western
North Dakota, depending on which model is followed, and ends up in
Manitoba by Sunday. The 150 mile difference in track of that mid
level low results in very little difference in sensible weather as
the surface low track is much more in line model to model.
Basically what this track and diffluent flow aloft means is a lot
of clouds and numerous showers. It also means warmer weather
ahead of the surface feature as winds veer to southerly, and an
increase in instability. We`d also expect a dry slot to work in,
likely through the central Dakotas, resulting in some sunshine on
Saturday.
The surface low track and tightening gradient would support windy
weather Saturday and Sunday, very windy southwest with an advisory
possibly needed.
As far as lightning, the better chances are along and south of
I-94 as CAPE and instability are highest, but still not
impressive, later today. storms could fire in the dry slot
Saturday, and conditions would favor strong storms, but they would
likely form in the central Dakotas, strengthening as they move
east.
.LONG TERM...(Saturday night through Thursday)
Issued at 438 AM CDT Fri Sep 23 2016
Gusty wind in the wake of the low continues for Sunday, again,
possibly advisory levels. Behind the mid level low on monday we`d
typically expect cooler air, however, models agree on strong H5
ridging, in response to the deepening low, into the forecast
area. This means back to normal, and even above normal
temperatures, to end September.
&&
.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 950 AM CDT Fri Sep 23 2016
Widespread IFR/MVFR conditions in stratus, rain showers and
thunderstorms are forecast across western and central North
Dakota today and tonight. A brief improvement to VFR is possible
at KBIS Saturday morning as dry air works into the storm system
impacting the area.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...AYD
SHORT TERM...JPM
LONG TERM...JPM
AVIATION...AYD
Area Forecast Discussion
National Weather Service Cheyenne WY
522 AM MDT FRI SEP 23 2016
.SHORT TERM...(Today through Saturday)
Issued at 310 AM MDT Fri Sep 23 2016
Widespread low clouds continue across areas along and east of the
Laramie Range. WYDOT obs from Cheyenne to the I-80 summit show vis
remaining mostly below a quarter mile so the dense fog advisory is
working out well. Will keep it going for central Laramie county
even though the fog has not developed at CYS yet. HRRR guidance
shows much quicker clearing through the morning compared to
yesterday. Models show the closed upper low currently near Salt
Lake City lifting northward into central WY by this evening. The
warm front will lift northward across the plains through the day
with southerly winds strengthening from I-25 eastward. Did
increase wind speeds over the Panhandle with the southern
Panhandle getting close to advisory level (fcst gusts to 35 kts)
by the late aftn.
Cold front is progged to be near the Laramie Range by the aftn,
and this will be focus for shower/tstm development. Went with
40-60 POPs over much of the plains of southeast WY during the aftn
as the HRRR/NCAR ensembles are in good agreement with the global
models. There will be a marginal risk of svr storms across the
plains and especially north of the warm front. This is due to CAPE
values of 500-1000 J/kg and excellent bulk shear. Storm activity
over the plains should begin to die down by the late evening with
the cold front pushing across the Panhandle by 06Z.
The other story with this storm system will be the orographic snow
over the Sierra Madre and Snowy Ranges by late tonight into
Saturday morning. Wet bulb zero heights are around 8500 ft MSL.
Moist westerly 700-500 mb flow on the backside of the upper low
will create favorable orographics, especially over the Sierra
Madre Range. Currently have 1-4 inches of snow over much of the
western mtns, which would be welcome news for the fires that have
been ongoing near the Sierra Madre Range. It will be breezy to
windy on Saturday with highs struggling to get above the mid 60s.
.LONG TERM...(Saturday night through Thursday)
Issued at 310 AM MDT Fri Sep 23 2016
Upper trough moves through the area Saturday night into Sunday.
Going to be cold as 700mb temperatures fall to -4C Sunday into
Monday.
Warmer and drier weather for the rest of the upcoming week as
ridge of high pressure builds back over the area.
&&
.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 519 AM MDT Fri Sep 23 2016
Looks like the HRRR guidance is maybe an hour fast on lifting
ceilings out in the Panhandle. So adjusted the forecast some to
continue low clouds out that way through the morning hours. Looks
like most areas should be VFR by 15-16Z or so. Still looking windy
this afternoon with the approach of the cold front with LAMP
guidance still showing wind gusts to 40kts for our Panhandle
airports.
&&
.FIRE WEATHER...
Issued at 310 AM MDT Fri Sep 23 2016
No fire weather concerns through the weekend. Temperatures will
cool across the entire area after today behind a cold front. Minimum
afternoon humidity values will mostly be above 25 percent through
the weekend. There will be a chance of showers and thunderstorms
through tonight across the region. A few inches of snow will be
possible tonight through Saturday morning over the Sierra Madre and
Snowy Ranges.
&&
.CYS Watches/Warnings/Advisories...
WY...Dense Fog Advisory until 7 AM MDT this morning for WYZ116>118.
NE...None.
&&
$$
SHORT TERM...ZF
LONG TERM...GCC
AVIATION...GCC
FIRE WEATHER...ZF
Area Forecast Discussion
National Weather Service Bismarck ND
309 PM CDT Fri Sep 23 2016
.SHORT TERM...(This evening through Saturday)
Issued at 248 PM CDT Fri Sep 23 2016
Severe thunderstorm potential southwest this evening and tonight
highlights the short term forecast.
The 15-18 UTC operational and experimental HRRR iterations
continue to show strong run to run consistency in developing
convection across eastern Wyoming this afternoon, and propagating
this convection into southwest North Dakota by 02-04 UTC,
sustained by a strengthening low level jet and a resurgence of
upper level forcing ejecting out of the intermountain west upper
level low. This is supported by the greater 12 UTC CAM suite.
These HRRR iterations continue to depict in their 2-5 km updraft
helicity fields tracks of 75-100+ m2/s2 across southwest North
Dakota, supporting the potential for organized convection
possibly in the form of elevated low topped supercells to survive
from Wyoming into southwest North Dakota. Large hail and damaging
winds are the primary threats given the likely elevated nature of
these storms.
For Saturday, followed a blend of the 12 UTC global suite given
good agreement amongst the larger scale guidance for the
aforementioned upper level low to propagate into southwest North
Dakota by early Saturday evening. A dry slot is favored across
much of the south central for Saturday, with wrap around
stratiform precipitation across the far west, and potentially more
convective precipitation across the north central and James River
Valley.
.LONG TERM...(Saturday night through Friday)
Issued at 248 PM CDT Fri Sep 23 2016
Strong winds across the west Saturday night with a dry forecast
for the remainder of the period thereafter highlight the extended
forecast.
Given good agreement, followed a blend of the 12 UTC global
guidance suites for most fields. The nearly stacked low from the
short term is forecast to propagate across North Dakota Saturday
night. All ingredients will be available for strong winds on the
backside of the low, with a tight pressure gradient and strong
cold air advection aided by isallobaric forcing. 0.5 km winds
around 50 kts are forecast across the west, which will have to be
monitored for the next few models runs should a high wind watch
become necessary across the west for Saturday night into Sunday.
Thereafter, broad upper level ridging builds across the central
CONUS Tuesday through the remainder of next week, signaling a
drier pattern with near to slightly above average temperatures.
&&
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 248 PM CDT Fri Sep 23 2016
Widespread IFR/MVFR conditions in stratus, fog, rain showers and
thunderstorms are forecast across western and central North Dakota
today and tonight. A brief improvement to VFR is possible at
KBIS/KJMS late tonight into Saturday morning as dry air works into
the storm system impacting the area.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...AYD
LONG TERM...AYD
AVIATION...AYD
Area Forecast Discussion
National Weather Service Taunton MA
410 PM EDT Fri Sep 23 2016
.SYNOPSIS...
A cold front will cross the region this evening, bringing lower
temperatures. A band of rain showers is also expected behind this
front later this evening into tonight, but amounts will be light.
Cool and dry weather will follow this weekend into early next
week. A slow-moving low pressure and cold front could lead to
some showers late next week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Latest mesoanalysis continues to show a very unfavorable
environment for supporting thunderstorms across southern New
England. Abundant clouds, as well as a stout low level inversion,
from earlier today has limited our warm up. More sunshine
developing across southern New England this afternoon. But it may
be a case of too little, too late.
Looking upstream, lots of lower clouds behind a cold front across
southern VT and NH. That indicates more abundant moisture, and the
possibility of some showers. Short-term guidance, such as the
HRRR and RAP, continues to indicate a higher likelihood of at
least some lightly measuring showers. Will continue with a brief
period of chance PoPs this evening. Only moderate confidence
rainfall chances will actually be as high as suggested by the
guidance with few radar returns upstream, despite the run-to-run
consistency of the guidance.
Band of rain showers will continue to press from north to south with
band of mid level frontogenesis/moisture behind a cold front. Much
cooler air will continue to work into the region tonight and northeast
winds will be a bit gusty along the coast.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Drier air will move in from the northwest, allowing for skies to
become mostly sunny during the morning. Mostly clear skies
continue through Saturday night.
Below normal temperatures during this time as well. If winds can
diminish enough, there is the remote possibility of some frost
across portions of the east slopes of the Berkshires Saturday
night, particularly in Franklin county. Will need to monitor this,
but think it is a low probability event at this time.
However, a fall-like
atmosphere will be in place with 850T between +3C and +5C. High
temps should still recover well into the 60s to near 70 given lots
of sunshine, but certainly be our first true taste of early fall.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights...
* Dry and cool weather continues through Monday with patchy
frost possible for some locations Sunday night.
* Precipitation chances increase Monday night thru Wednesday
night, with a return to seasonable temperatures.
Overview and model preferences...
Omega block over the Mississippi Valley continues to translate east
and gradually deamplify through the middle of the upcoming week.
The 23/12Z model suite begins to diverge around 12Z Monday, with the
ECMWF notably weaker, and thus more progressive, with its handling
of the closed low over the Great Lakes. We leaned toward the slower
and more amplified GFS solution, given the interaction of several
pieces of energy, as the ECMWF may be breaking down the block too
quickly. But confidence in the details is below average, and will
remain so, until the models better resolve competing shortwave
energy interacting with the closed low.
Details...
Sunday and Monday...
Northwest flow aloft will keep the region dry during this time frame,
as Canadian high pressure crests across the region by Monday morning.
Given the combo of a dry airmass in place, as well as a decoupled
boundary layer, we anticipate ideal radiational cooling conditions
to occur Sunday night. Thus, we went below guidance on temperatures,
which may bottom out in the low to mid 30s for portions of the
region. In particular, the interior locations northwest of the Mass
Pike and I-495, as well as interior southeast Massachusetts, have
the potential for their first frost of the season. Otherwise, there
will be an increase in mid and high level cloudiness on Monday, as
a warm front approaches the region.
Monday night thru Wednesday... There is still uncertainty with the
timing of a cold front during this time frame, with the more
progressive ECMWF keying in on Tuesday morning, while the GFS holds
off until Wednesday afternoon. We leaned more toward the GFS, and
focused PoPs in the Monday night to Wednesday morning period. We
also kept consistency with the previous forecast, with the greatest
chance of precip focused in the late Tuesday thru early Wednesday
time frame, when the deepest moisture and strongest dynamics
coincide. This system does not have much in the way of moisture to
work with, as Precipitable Water values only rise to 1.5 inches, so
rainfall will be generally light. We also cannot rule out a rumble
of thunder along the south coast Monday night into early Tuesday, as
some elevated instability traverses this area.
Thu and Fri...
Still some uncertainty regarding how quickly the upper low departs
the region. We maintained NIL to low PoPs, especially considering
the amount of moisture along the back side of this feature.
&&
.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight...Moderate to high confidence. A period of MVFR CIGS in a
band of showers are likely behind a cold front. Northeast wind
gusts of 20 to 25 knots expected along the coast.
Saturday...High confidence. Mainly VFR. Any leftover MVFR Cigs,
and perhaps some patchy early morning fog in the typical
locations, will improve to VFR by mid morning.
Saturday night...High confidence. VFR.
KBOS TAF...Moderate confidence in TAF due to shower coverage. High
confidence in winds. Wind shift to the northeast with brief
gusts to 25 kt possible between 23/20Z and 24/06Z, along with a
period of MVFR CIGS and showers.
KBDL TAF...Moderate confidence in TAF due to shower coverage. High
confidence in winds.
Outlook /Sunday through Wednesday/...
Sun thru Mon...High confidence. Predominantly VFR. Northwest
winds may gust to 25 kt near shore on Sunday.
Mon night thru Wed...Moderate confidence.
Localized MVFR conditions possible in showers, mainly Tue night into
Wed, with uncertainty with regard to timing. Otherwise VFR.
&&
.MARINE...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight...High confidence. A strong cold front should result in a
period of northeast wind gusts up to 25 knots, and 3 to 6 foot
seas across our open waters, early this evening into the
overnight hours. Small craft headlines posted for all waters
except Narragansett Bay.
Saturday into Saturday night...High confidence. Leftover 25 kt
wind gusts diminish by mid morning as pressure gradient weakens.
However, small craft headlines will continue across our outer
waters into mid afternoon from leftover swell. These seas should
finally drop below small craft advisory thresholds by late
afternoon. Increasing north to northwest winds with a stronger
surge of colder air over the waters. Not confident there will be a
long period of sub advisory winds. So, will continue the small
craft advisory into Saturday night across the outer coastal
waters.
Outlook /Sunday through Wednesday/...
Sunday and Sunday night...High confidence.
Small craft advisory conditions prevail. Northwest wind gusts
around 25 knots Sunday, with seas 5 to 6 feet expected into
Sunday night.
Monday...
Conditions are expected to remain below Small Craft Advisory
criteria with high pressure building over the waters.
Monday night thru Wednesday...
An approaching storm system will lead to a period of southerly flow
over the waters during this time frame. Small Craft Advisory criteria
is possible during this period, however, the timing is uncertain.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT
Saturday for ANZ231>235-237.
Small Craft Advisory until 11 PM EDT this evening for ANZ230.
Small Craft Advisory until 6 AM EDT Sunday for ANZ250.
Small Craft Advisory until 8 AM EDT Saturday for ANZ251.
Small Craft Advisory from 8 PM this evening to 6 AM EDT Sunday
for ANZ254>256.
&&
$$
SYNOPSIS...Belk/Franck
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...Franck
AVIATION...Belk/Franck
MARINE...Belk/Franck
Area Forecast Discussion
National Weather Service Gray ME
531 PM EDT Fri Sep 23 2016
.SYNOPSIS...
Showers will continue along a cold front through this evening
over southern New Hampshire and far southwestern Maine before much
cooler and drier air arrives for the weekend as Canadian high
pressure builds into the region. This will bring the potential for
frost or freezing conditions Saturday and Sunday nights...
especially over northern areas. Gradually moderating temperatures
are expected Monday before another approaching cold front brings
the threat for showers on Tuesday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
530 PM Update...Have updated the grids for the next few hours
based on latest trends in observations and mesoscale model
guidance. The result was little change to the going forecast.
However, we did tighten up the PoP gradient a little bit across srn
NH for this evening based on latest radar mosaic loops and HRRR
guidance. Narrow stripe of showers is beginning to take shape
across Upstate NY to the NW of ALB. This area of showers is
expected to mainly affect Cheshire and Hillsborough counties this
evening.
Previous discussion...
High Impact Weather Potential: Patchy frost in the far northern
valleys possible.
Current Pattern: Water vapor imagery early this afternoon shows an
onslaught of northwesterly flow extending from Manitoba south and
east to a leading shortwave now pressing through New England. This
shortwave is interacting with a modest /although thinning/ moisture
plume along the east coast to produce multiple bands of showers as
it pushes south and east. Also of interest is an area of darkening
in water vapor imagery over western Ontario which represents another
upstream shortwave that will sharpen as it rapidly pushes southeast
into New England during the first half of the night. Beyond
this...sprawling 1030mb high pressure over northern Ontario will
begin to push toward the region...bringing a clearing/drying/
cooling trend to the area. Forecast concerns are thus focused on
precipitation potential through this evening...and temperatures as
the continental polar airmass arrives tonight.
Through Early Evening: Shower activity has dwindled markedly over
the past 1-2 hours...so through 6pm expect little more than a few
sprinkles/very light rain showers over southern areas with some
breaks in the clouds opening up over northern areas.
Tonight: High resolution near term guidance consensus has been
honing in on another period of more widespread shower activity over
southern NH and far southwestern ME this evening as aforementioned
shortwave over Ontario sharpens and interacts with H8 frontal zone.
The best window of opportunity for rain looks to be between 8pm
and midnight...generally south of a LEB-PWM line. This will
certainly help to boost meager rainfall totals in these areas thus
far...with another few tenths of an inch of rain quite possible.
Beyond this...cold and dry advection will be the rule with gradual
clearing from north to south as PWATs retreat back below 0.5".
Temperatures will fall rapidly...particularly with partial
clearing after midnight...with consensus lows in the upper 30s
north to mid/upper 40s south looking reasonable. Can/t rule out a
few patches of frost over the far north...but not widespread /or
confident/ enough to warrant a county-based headline.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
High Impact Weather Potential: Frost/Freeze Potential Saturday
Night.
Pattern: The short term forecast period will be dominated by
continued northwesterly flow aloft given highly amplified
trough/ridge/trough pattern across North America...with large
surface high over eastern Ontario Saturday morning remaining nearly
stationary through this forecast period. T8s start the period near
the freezing mark...and gradually settle lower by Saturday night
with these values representing -1 to -2 sigma departures from
climatology. PWATs will similarly be in the -1 to -2 sigma
range...promising little in the way of sensible weather through the
period. Forecast concerns will center around temperatures Saturday
night as the coolest night of the early fall season is expected.
Saturday: Longwave trough will continue to deepen along the east
coast of NOAM as sharp longwave ridging over the central portion
of the continent slowly builds and moves east. This will maintain
northwesterly flow through the column over our region...although
any significant cool advection will be over by daybreak. BUFKIT
profiles agree with CU rule suggestions from the guidance
indicating some SCT cumulus development in the mountains...with
very little in the way of cloudiness making it to the coast.
So...expect a mostly sunny day for most spots. T8s will only be
around +1-3C...so expect northern areas to remain in the
50s...with areas south of the mountains to reach the lower/middle
60s. Given the robust gradient aloft...expect northwesterly winds
10-20kts for the day...adding a bit of chill to the air.
Saturday Night: High pressure remains north and west of the area
with PWATs falling to around 0.25" in continental polar airmass.
Expect any afternoon cumulus to clear...with a chilly night in
store across the region.
Primary factor potentially limiting the chill will be an ongoing
breeze as 1000mb geostrophic winds remain 20-30kts overnight likely
keeping many locations coupled. Honestly...this looks more like a
freeze vs. no freeze situation with perhaps too much wind to support
frost. Given the breeze...have kept overnight lows a bit higher
than statistical guidance. Breeze will also restrict widespread
fog...but given how cool temperatures will be...some CT valley
locations will still probably see some patches.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Chance of High Impact Weather: Minimal.
Where for the last few months 500mb blocking was hard to come by
south of 50 N, we are finally starting to see sow blocks develop
that will bring troughs down in the 30-40 N range. The models do
not show stable blocking, but it is enough to bring temps to
around normal with some fluctuations either side of normal through
the long range. However, with the instability of the blocking,
systems will be mobile and not very strong, so any chance for a
soaking rain remains low through next week.
The cold air will continue to stream in Sunday, as 500 mb trough
works through in the morning. this air is very dry, but should
produce some clouds in the mountains Sunday, maybe become mostly
cloudy for a few hours. The coastal plain will see more sun in the
downslope as N-NW winds pick up in the 10-20 mph with some higher
gusts. Highs will be cool, and a few degrees below normal ranging
from the low to mid 50s in the mountains to the low 60s in srn NH
and along the ME coast.
Sunday night will turn out to be an very good rad cooling night as
sfc high builds in ands winds die off quickly with clearing
skies. Lows will range from the mid-upper 30s in the mountains to
the low 40s along the coast and in urban areas of the Merrimack
valley. This will bring the threat of frost to almost everywhereexcept
the immediate coast.
Light winds shift to the SW on Monday as the high shifts offshore
and it looks to be mainly a sunny day with highs a few degrees
warmer than Sunday, bring temps to around normal, generally in the
60s. The next chance for rain will be in the Mon night thru Wed
time frame as 500mb closed low tracks NE out of the great lakes
and drags a cold front across the region. The Euro is a little
progressive the fropa, ad moving the rain out by Tue night, with
the GFS lingering it. However, the Euro also merges the two closed
500 lows to our north and spins the resultant low back SW and
brings it just N of ME. This would result in cooler temps late in
the week than the GFS. Went with Superblend, which split the
difference which keeps temps around normal Wed-Fri, though if the
Euro is right, they would be cooler, and if the GFS they would be
warmer.
&&
.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
Short Term...
Summary: A cold front will push south of the region this evening
with high pressure building in it/s wake through Saturday and
remaining over the region through Saturday night.
Restrictions: Band of showers will bring MVFR restrictions northern
terminals...with CON/MHT/PWM/RKD likely seeing brief drops to MVFR.
Conditions improve to VFR as showers depart this evening...with
LIFR/IFR fog likely HIE/LEB...and possible CON/AUG. VFR for Saturday
/ Saturday night with the exception again being overnight fog
HIE/LEB.
Winds: Northwesterly winds 10g16kts this afternoon will diminish to
5-10kts /light and variable in the valleys/ for the overnight before
increasing to 12g20kts from the northwest for the day Saturday.
Northwest winds will diminish to below 10kts again Saturday night.
LLWS: No LLWS expected through Saturday night.
Thunder: Very slight chance of thunder MHT through 21UTC...but
chance not great enough to mention in TAF. No thunder beyond this
through Saturday night.
Long Term...Sunday could continue to some N-NW wind gusts in the
20-25 kt range, but VFR Expected Sun-Mon. Some showers are
possible Tuesday and Tue night, and could see a period of flight
restrictions ahead of cold front Tue afternoon and night.
&&
.MARINE...
Short Term...Strengthening northerly winds tonight will bring
winds/seas close to marginal SCA values for the overnight before
shifting northwest on Saturday...with winds/waves remaining near
marginal SCA values through Saturday night...after a brief lull
in the winds early Saturday.
Long Term...Borderline SCA possible Sunday in N-NW winds, but
winds diminish by Sunday evening and stay below SCA through Wed.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ150-152-
154.
&&
$$
SYNOPSIS...Arnott
NEAR TERM UPDATE...Ekster
SHORT TERM...Arnott
LONG TERM...Cempa
AVIATION...Arnott/Cempa
MARINE...Arnott/Cempa
Area Forecast Discussion
National Weather Service Lincoln IL
310 PM CDT FRI SEP 23 2016
.SHORT TERM...(This evening through Saturday)
ISSUED AT 310 PM CDT Fri Sep 23 2016
A surface boundary/back door cold front just south of I-74 this
afternoon will continue to slowly sag sw across central IL into
tonight, with 1029 mb surface high pressure over Ontario ridging
into the Great Lakes region. Latest run of HRRR is now showing
some convection from I-74 northeast late this afternoon and early
evening but feel its coverage is too high and earlier runs of HRRR
were dry. Current radar mosaic shows just isolated very light
showers ne of Vermilion county IL which latest RUC model shows, so
will keep pops at 10% over northeast CWA through 00Z/7 pm today.
Dewpoints in the 60s across CWA and models show some increasing
low level moisture near and northeast of the front tonight
especially overnight into early Saturday morning allowing patchy
fog to form with light wind regime.
The latest forecast models continue to have a strong upper level
ridge over IL on Saturday with 500 mb heights around 589 dm. This
should bring another very warm summerlike day to the area with
highs 85-90F and dewpoints in the mid to upper 60s.
&&
.LONG TERM...(Saturday night through Friday)
ISSUED AT 310 PM CDT Fri Sep 23 2016
The main focus for this forecast cycle will be the frontal passage
and associated precipitation for this weekend. The 12z models seem
to have better agreement on the a more progressive theme to the
upper level pattern progression. The Canadian NH no longer cuts off
a low behind the front, for later passage mid-week. The consensus
indicates the occluded surface and upper low pressure centers will
move from the western Dakotas Saturday afternoon northeast into
Manitoba and western Ontario by Sunday evening. Then the upper
trough is projected to deepen toward the southeast, into the central
Great Lakes region. This will provide the reinforcing push of cooler
air for our mid-week cool down.
As for the sensible weather during this scenario, we are looking for
increasing clouds Saturday night as the cold front moves half way
across Iowa. We included a narrow ribbon of slight chance PoPs along
our far western counties in Knox, Fulton and Schuyler counties. The
strongest forcing for precip will generally remain north of our
forecast area on Sunday as the surface and upper lows lift into
western Ontario. As a result, the front circulation and low level
moisture convergence will most likely be weakening during FROPA
Sunday afternoon and early evening. Support for any thunderstorms
will come from high boundary layer moisture with dewpoints around 70
in the pre-frontal air mass. Instability params will support a line
of storms, with MUCAPES of 1500-2200 J/kg Sunday afternoon. Bulk
shear will be marginal, in the 20-25kt range. The better agreement
on frontal timing has increased confidence in precip on Sunday
afternoon/eve, and PoPs were increased to Likely /60-70%/ north of
I-72, progressing from west to east between Noon and midnight.
Precip chances will linger into Monday as a secondary lobe of energy
rotates through the upper trough before it departs to the east on
Tuesday. A much cooler and drier air mass will settle into Illinois
for Tuesday through Thursday. Highs will be below normal in the low
70s on Tuesday, then warm to near normal in the mid to upper 70s for
Thursday, with upper 70s across the board on Friday. No
precipitation is expected from Monday night through Friday, and
possibly into next weekend.
&&
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1253 PM CDT Fri Sep 23 2016
VFR conditions will continue through this evening across the
central IL airports with scattered cumulus clouds of 4-7k ft and
scattered to broken cirrus clouds. A frontal boundary just south
of PIA and BMI will push south of I-72 during this afternoon with
light and variable winds becoming more ENE and staying less than
10 kts. Some fog could develop during overnight and bring MVFR
conditions and possibly as low as IFR between 08Z-14Z. Strong
upper level ridge building over IL during the next 24 hours will
keep it dry.
&&
.ILX Watches/Warnings/Advisories...
NONE.
&&
$$
SHORT TERM...07
LONG TERM...Shimon
AVIATION...07
Area Forecast Discussion
National Weather Service Indianapolis IN
700 PM EDT FRI SEP 23 2016
.UPDATE...
The AVIATION section has been updated below.
&&
.SYNOPSIS...
Issued at 141 PM EDT Fri Sep 23 2016
A large ridge of High Pressure over the plains states is expected
to build across the Ohio valley and Great Lakes Tonight and
Saturday. Meanwhile...High pressure over Ontario will also build
southwest...providing dry but warm temperatures for central;
Indiana this weekend.
The upper ridge will moves east of Indiana by Sunday
night...allowing a Cold front to approach the area for Sunday
night and Monday. This will be the next best chance for showers or
storms as this front passes early next week. Cooler High pressure
in the wake of the front is expected to arrive by the middle of
the next work week. This will lead to more seasonable temperatures
then.
&&
.NEAR TERM /Tonight/...
Issued at 141 PM EDT Fri Sep 23 2016
Surface analysis early this afternoon shows broad high pressure
in place across the Ohio Valley. A back door cold front was found
from Western NY to NW Ohio...across NRN Indiana to Iowa. A few
showers were found on the north side of this front. Wind fields
here show well defined northeast surface flow in the wake of the
front.
Main forcing mechanism through the afternoon appears to be daytime
heating. HRRR blossoms precip north of the front late this
afternoon...but it diminishes quickly by the evening when heating
is lost. Forecast soundings continue to show some limited
instability...but feel that the HRRR...appears a bit over done.
However...will include a low chc for a shower near the
front...mainly far northern areas late this afternoon. Grids will
be dry after 00z as heating will be lost and forecast soundings
continue to reveal a dry column and time heights show subsidence.
Back door cold front is expected to make slow and stead progress
southwest tonight as the ridging aloft to our west builds across
Indiana. THe lower level boundary may help to provide some clouds
during the night as time heights suggest some lower level moisture
available. Thus will trend toward a partly cloud sky
overnight...with a blend on temps.
&&
.SHORT TERM /Saturday through Monday/...
Issued at 141 PM EDT Fri Sep 23 2016
Dry Weather is expected for much of the weekend as HIgh pressure
northeast of Indiana and the previously Mentioned ridging aloft
continue to dominate Indiana/s weather. Models suggesting
cooler...northeast flow on Saturday and Sunday and this should
provide slightly cooler temperatures...however it will still be
above seasonal normals. Forecast soundings on both Saturday and
Sunday Afternoon indicate convective temperatures that can be
reached...however CAPE is very limited. Thus will just trend
toward partly Cloudy skies both afternoons...again trending
slightly warmer than a blend on Highs.
Late Sunday night and Monday appear to be the better times for
precip. NAM and GFS push the upper ridge east of Indiana by that
time as a deep upper low pushes out of the Central Canada and into
the Great lakes and Ohio valley. This feature looks to push as
cold front across the state with ample dynamics and will include
raise pops...particularly monday as these features pass. Forecast
soundings show best saturation on Late Sunday night and on Monday. We
should continue to be mindful that these features often progress
more slowly due to the strong departing ridge ahead of the front.
&&
.LONG TERM /Monday Night through Friday/...
Issued at 159 PM EDT Fri Sep 23 2016
Models are more progressive in recent runs with large low pressure
system moving through the Great Lakes early to mid week. The cold
front is now progged to be through the area prior to the start of
the Long Term period, with broad surface high pressure moving into
the area and dominating through the remainder of the period. Thus
will carry a dry forecast throughout the period. As is noted
above, however, there remains uncertainty in the departure of this
system.
Temperatures throughout the period will be pleasant, and much more
in line with climatological normals than recent days.
&&
.AVIATION /Discussion for the 24/00Z TAF Issuance/...
Issued at 700 PM EDT Fri Sep 23 2016
Confidence is good that VFR conditions will deteriorate to MVFR or
worse overnight in fog and or stratus as a frontal boundary slides
drops slowly south over central Indiana. The local foggy program
slightly favors stratus over fog, while the GFS LAMP favors fog and
the SREF is more in the middle. At any rate, post-frontal IFR
conditions will become more likely at LAF after 10z. The other sites
could see MVFR or worse, but confidence at those sites is lower.
Winds will be calm or very light and variable tonight and becoming
east and northeast 5 knots or less on Saturday.
&&
.IND Watches/Warnings/Advisories...NONE.
&&
$$
SYNOPSIS...PUMA
NEAR TERM...PUMA
SHORT TERM...PUMA
LONG TERM...NIELD
AVIATION...MK
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
408 PM CDT FRI SEP 23 2016
.SHORT TERM...(This evening through Saturday)
Issued at 408 PM CDT Fri Sep 23 2016
Another day and it`s more of the same for this week with PWATs near
2 inches (exceeding climatological records for the end of
September)and more rain falling from the skies. The band out there
now is a waa band that`s going up on elevated instability gradient
based in the h85 to h7 layer. Though radar may not look all that
impressive, the high PWATs are once again resulting in efficient
rainfall producers, with KMPX dual pol radar estimates showing about
an inch of rain was being produced by the band. Only hi-res models
that have had much of a handle on this are ones that are rapid
update (i.e. the hrrr) and we like the idea of this band continuing
northeast into northern MN and northwest Wisconsin this evening
while also weakening in terms of rainfall intensity. The weakening
is the result of the instability feeding these showers not following
them off to the northeast.
For the rest of tonight, it will be another night of low stratus as
we remain north of the warm front. As for the warm front, it is
quite impressive this afternoon. It just sneaks into SW MN where
Luverne was 86 degrees at 3 pm. At the same time, Pipestone right on
the front was 77, while by the time you got up to Marshall it was
only 65. And to boot, 90s were not all that far away with Yankton,
SD sitting at 91. This warm front will not start lifting north until
Saturday morning and will make it about as far north as the upper MN
River Valley before it starts getting swept up by a cold front that
will be pushing through Saturday night. As we have seen today, this
is a very warm warm sector and if we get any clearing in south
central MN tomorrow, then highs near 90 will be possible. However,
for most it will be another day of extensive cloud cover and little
diurnal temperature range.
For precip, as we saw this morning, there will be potential for
drizzle development here north of the warm front overnight, but once
the band currently over the area moves off to the northeast, no
significant precip arrives until the cold front starts nudging into
western MN late Saturday afternoon. There was a general slowing of
how quickly these storms get here, so did slow down how quickly we
bring back PoPs tomorrow afternoon. There will be plenty of low
level shear to support a severe weather threat, but extensive cloud
cover will greatly hamper atmospheric destabilization. In addition,
capping will be weak tomorrow, so once we develop instability, the
atmosphere will quickly consume it. Still the top analog for the
NAM forecast on Saturday of October 8, 1997 had a good deal of wind
reports with a line of storms that developed ahead of a cold front,
so the severe risk tomorrow is not negligible.
Of course the one thing we don`t need right now is more rain, but
that`s what is coming. In addition, the NAM/GFS again show PWATs up
around 2 inches ahead of the front, so it`s back to more efficient
rainfall producers and heavy rainfall. Fortunately the progressive
nature of the activity looks to limit the flood threat with a
general model consensus on a fairly widespread 0.5" to 1" out of
this front. However, the NAM shows some streaks where around 2" are
possible and given the hydrologic conditions of much of the area,
even modest amounts such as that could lead to excessive rainfall
issues once again and the slight risk of excessive rainfall from the
WPC is warranted.
.LONG TERM...(Saturday night through Friday)
Issued at 408 PM CDT Fri Sep 23 2016
A long line of showers and thunderstorms stretching from the
Canadian border to the Mexican border will develop Saturday
afternoon and track east along a cold front Saturday night. Good
forcing along the front and very high pwat values near 2 inches
should keep the band intact through the CWA. Raised pops further
from previous forecasts to around 100 over eastern MN and over 80
just about everywhere else.
The severe threat appears marginal with a nearly saturated
atmosphere and poor lapse rates. Still, should expect some gusty
winds with the band of heaviest storms with decent low level
shear. Cannot rule out a weak QLCS tornado as well with good
veering profiles in the lower levels in areas that can achieve
better instability.
The dry slot will push in immediately behind the front with some
clearing skies Sunday morning. The upper low will then push east
across the Upper Mississippi Valley bringing widespread stratus
across the region and scattered showers for the northern halves of
Minnesota and Wisconsin. Depending how long it takes the upper low
to eject northeast, we could see some showers linger into Monday
night. GFS and GEM are the slowest, with the ECMWF the quickest.
Usually the slower solutions win out in these circumstances so
maintained such PoPs north of I-94 through Monday night, but did
reduce them Tuesday and Tuesday night.
Mid to late week looks quite pleasant with surface ridging pushing
east across the eastern two thirds of the nation. A mid level
ridge will build across the central CONUS, very likely keeping
dry weather in place for much of the week. Southeast to south flow
will also bring warmer temperatures.
&&
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 123 PM CDT Fri Sep 23 2016
Elevated instability pushing in is forcing a band of
shra/tsra across MN. The HRRR has had a good handle on it, though
has not been building it far enough southeast. This band of shra
will lift through AXN/MSP/STC/RNH on its way to northern MN and
NW WI. In its wake, we remain north of the surface warm front
tonight, which means more widespread IFR stratus through tonight,
with IFR/MVFR vis developing as well, though that will be closer
to the warm front, so a bigger issue from west central through
south central MN. We may see cigs lift some tomorrow afternoon
ahead of the cold front, with the next chance for TSRA lingering
just outside current TAF period.
KMSP...band of shra with embedded tsra continues to build
southeast as it moves to the northeast and at its current pace
will be to MSP around 20Z. Has become obvious more than a vcsh
was needed, so started shra with a vcts at 20z. Rain shouldn`t
last for much more than an hour, but in it`s wake is extensive
IFR and lower stratus, which is a sign of our future tonight.
/OUTLOOK FOR KMSP/
Sun...MVFR/-SHRA/-TSRA early, bcmg VFR. Wind W 10g20 kts.
Mon...Chc MVFR/-SHRA. Wind WNW 10g15 kts.
Tue...Chc MVFR early then VFR. Wind NW 5-10 kts.
&&
.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&
$$
SHORT TERM...MPG
LONG TERM...BORGHOFF
AVIATION...MPG
Area Forecast Discussion
National Weather Service Pocatello ID
150 PM MDT FRI SEP 23 2016
.DISCUSSION...Early afternoon satellite and radar imagery was
showing the upper low centered near Salt Lake City with diminishing
radar returns across SE Idaho. Numerical models continue to show the
low lifting NE into Wyoming late this afternoon and eventually into
SW North Dakota by Saturday afternoon. The NAM and GFS guidance
appear to be overdoing QPF totals over SE Idaho (especially this
past morning) and thus are falling under a specter of doubt whereas
the HRRR and UofAriz WRF (two high-def short range models) are
showing something more akin to what has been observed through early
afternoon with diminishing returns this past morning and scattered
showers continuing across the ERN highlands this afternoon and a
continuous area of light rain over the ERN Magic Valley in the NW
quad of the exiting low. Am favoring the two high-def models at this
point and have decreased the precip potential this evening while
leaving elevated chances across the ERN highlands tonight due to the
passing low while drier conditions slowly spread into the CNTRL
mountains/ERN Magic Valley. With that in mind, I have dropped the
Flash Flood Watch for the South-Central Highlands, Caribou
Highlands, and Idaho Portion of the Northern Wasatch for the
remainder of this afternoon and evening. Snow levels are also
expected to remain near 8000 to 8500 MSL across the NRN Wasatch this
evening greatly reducing the likely hood of seeing any significant
snow accumulations across the mountains near Bear Lake and thus I
will allow the special weather statement for that areas 1st snowfall
to go by the wayside as well.
A ridge of high pressure builds across the NW states Sunday through
Tuesday resulting in dry conditions. We may see a cold start Sunday
morning with possible freeze warnings in the Snake Plain but
otherwise temperatures should warm under the ridge peaking above
seasonal normals Tuesday/Wednesday. By Wednesday afternoon the models
are now showing the potential for a weak sub-tropical disturbance to
lift NE through the CNTRL Rockies as a PAC trough takes shape off
the NW coast. The NW trough eventually edges inland sometime
Thursday/Friday resulting in increasing SW winds across the region
and a chance/slight chance mention of showers favoring the
mountains. Huston
&&
.AVIATION...One airdrome, KSUN, has already broken out permanently
from the effects of the current low pressure lingering over the
Great Basin and northern Rockies. The other four airports will soon
follow suit. KIDA should be next as northerly flow sets up a
downslope and drying influence on the airport. KBYI has to contend
with an upslope condition in the same flow, so it will continue to
receive heavy rain, but once the wind shifts to the west this
evening, conditions will lift quickly. KPIH and KDIJ will be the
last to have clearing conditions as the low departs to the east. The
main forecast problem is what the wind will do today at KBYI. Using
a local study, it is indicating near Wind Advisory criteria, so have
lowered wind there to 20G30KT. The current set up is rather weak on
cold air advection, and the 500mb and 700mb flow is weak. Messick
&&
.FIRE WEATHER...It is a tale of two areas; south and east of the
Snake River, precipitation amounts for the last two days are
approaching 1.50 inches, while areas to the north and northwest have
not been hit as hard by the rain. High pressure will move in behind
the low that brought all this rain late tonight and into Sat. This
will start a warming and drying trend that should last at least into
Wed, and perhaps even to next Fri. This is a long time to dry, but
temperatures will struggle to even reach 80 degrees F, which makes
it difficult for humidity to reach the teens. The one location that
may be able to get low humidity is the Salmon-Challis NF and nearby
BLM land, where dewpoints will lower into the 20s with the dry
northerly flow on Sat and Sun. Fortunately, humidity criterion are
not alone in a critical fire weather pattern. Moderate wind is also
a minimum requirement, and as usual underneath high pressure, that
will be difficult to get anywhere except at very high elevation.
Messick
&&
.PIH Watches/Warnings/Advisories...None.
&&
$$
Area Forecast Discussion
National Weather Service Pueblo CO
344 PM MDT FRI SEP 23 2016
.SHORT TERM...(This evening through Saturday)
Issued at 301 PM MDT Fri Sep 23 2016
...A variety of high impact weather to continue across southern CO...
An intense upper low over NW UT/SW WY will continue to lift
northeastward with trailing trof axis swinging across southern CO
during the evening hours...a little behind earlier model
projections. This will put the brunt of the energy crossing the
eastern mountains between 00z and 03z with strong downward forcing
coming in quickly behind. Dry line has been slow to sharpen
up...though in last hour dew point at COS plummeted from 39 to 15
degrees F...so once winds shift out of the southwest to west...it
shouldn`t be too long before rapid drying takes place. Winds have
been gusting to 40-50 mph at times and this will continue through
the evening and overall Red Flag Warning still looks on track. To
the east of the dryline...high res models are developing a broken
line of thunderstorms between 4 PM and 5 PM. Dew points in the lower
50s yield mixed layer CAPE values of 1000 J/kg in SPC meso analysis.
Deep layer shears will be running around 30-40 kts...so potential
for one or two severe thunderstorms across the eastern counties
still looks possible. Storms will be moving rapidly north
northeastward with HRRR showing most of the activity done by 06z.
Given high based nature to thunderstorms...main threat still looks
to be winds over 60 mph and hail to around 1 inch in diameter.
As the upper low lifts northeastward should see activity tail off
from west to east...though northern portions of the Continental
Divide may continue to see off and on snow showers through the
overnight hours. Cold front moves in overnight...and a widespread
freeze still looks likely for the San Luis Valley. Have upgraded the
freeze watch to a freeze warning. Temperatures will be cooler
elsewhere...but winds should keep temperatures from dropping too
close to the freezing mark.
Saturday will be cooler behind the front...though secondary push of
cooler air will approach the Palmer Divide during the afternoon.
Just enough moisture will be present along the CONTDVD and northern
portions of the southeast mountains for some isolated to scattered
showers and thunderstorms to redevelop...but overall...any
precipitation looks light at this point. -KT
.LONG TERM...(Saturday night through Friday)
Issued at 301 PM MDT Fri Sep 23 2016
...Feeling more like Fall on Sunday...
The global models have come into better agreement today. The
strong upper low moving through W CO today will split this
weekend, with most of the energy lifting off to the NE. The base
of the trough will cut off over W NM, then slowly eject to the NE
during the mid to latter portion of the coming week.
Sat night...the main low will be well north of our area...over
the Nrn High Plains, while the trough axis is moving through E CO
and the base of the trough beginning to split and cut off over NM.
This will be the coldest air mass of the extended, with H7 temps
getting down to around zero degrees over Teller County by early
Sun morning. So...there could be a few snow showers above 9000
feet early Sunday, and possibly some light localized accums...but
significant or widespread snow appears unlikely, and the latest
model trends are for less QPF over the area.
Main impact from this system will be considerably cooler wx on
Sunday, with high temps only in the 60s for the Plains and 40s
for the mts. WIll clear out pretty quickly Sun morning-afternoon,
leaving our area with building high pressure from the west, which
will keep us dry through at least Tuesday. Temps will gradually
increase during this time period.
By early Wednesday, the cut-off low to our south will finally
begin moving into SW CO. This system will be much weaker than the
current upper low, and with the Southwesterly trajectory, will
also be quite a bit warmer aloft. So, snow levels will likely stay
pretty high for the last week in September, generally above 12000
feet. Showers will be on the increase, especially for the latter
part of Wed into early Thu. Have left mention of TS in the grids
for this period since there will be some modest instability with
the upper low. But for the balance of the forecast period,
climatology does not favor widespread TS, so left any precip as
Showers for the rest of this period.
Once the second upper low moves through from the SW, our area will
likely stay in an unsettled pattern with shortwaves moving through
the Central Rockies. Current forecast assumes southwest flow over
the CWA, so temps will remain generally above average. Rose
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 301 PM MDT Fri Sep 23 2016
South winds 25-40 KTS will shift around from the west during the
late afternoon and early evening and remain gusty through 03-04z
before gradually diminishing. TAF sites will remain VFR...but
CONTDVD region will see off and on IFR to LIFR conditions in SHRASN
through the early evening. Isolated TSRA will be possible to the
east of the KLHX this evening...with the potential for a strong to
severe storm or two through the evening hours. Clearing will take
place through the evening...though some IFR to MVFR stratus may
persist along the CONTDVD through Saturday morning. Winds will be
much lighter on Saturday with another cold front expected to drop
through the plains late Sat afternoon and early Sunday evening. -KT
&&
.PUB Watches/Warnings/Advisories...
Red Flag Warning until 8 PM MDT this evening for COZ226>233.
Freeze Warning from midnight tonight to 9 AM MDT Saturday for
COZ069>071.
&&
$$
SHORT TERM...KT
LONG TERM...ROSE
AVIATION...KT
Area Forecast Discussion
National Weather Service SAN ANGELO TX
349 PM CDT FRI SEP 23 2016
.SHORT TERM...
(Tonight and Saturday)
The primary heavy rainfall event starts to occur Saturday Night, so
the long term part of the discussion will deal with those concerns.
For tonight, visible satellite shows some agitated cu across much of
West Central Texas, but the latest HRRR is showing only a few
isolated showers and storms developing this evening. This pretty
well covered in the current forecasts so left that part of it alone.
Convection will likely develop tonight to the west across the South
Plains and Permian Basin as lift ahead of the large upper level
trough axis begins to move into West Texas. These storms should
slide east and increase in coverage Saturday afternoon. Have
increased rain chances across the northwest Big Country, mainly
north of a Sweetwater to Throckmorton line for Saturday afternoon.
Areas farther south will wait for Saturday Night and beyond for
their best chances.
As for temperatures, mild again tonight as low clouds develop across
much of the area by morning. Increasing cloud cover during the day
on Saturday will begin to cut into afternoon highs. Still, enough
sunshine in the afternoon for upper 80s and lower 90s, the hottest
day we will likely see for the next week.
07
.LONG TERM...
(Saturday Night through next Friday)
The main focus is with the likelihood of heavy rainfall and the
threat for flooding this weekend into Monday.
By Saturday evening, an upper low is forecast to be over the
Montana/ North Dakota border, with an upper trough extending south
across western New Mexico. The GFS and ECMWF are in better agreement
with the development of a closed low over southwestern New Mexico
Saturday night. This low is progged to drop slowly south-southwest
into Mexico on Sunday, and then retrograde slowly Sunday night into
northwestern Mexico by Monday evening. With the northern part of the
aforementioned trough progged to move east across the northern
Plains on Sunday, trailing portion of a cold front is progged to
move south into our northern counties Sunday afternoon, and then
to make slow progress south through the rest of our area Sunday
night and early Monday morning.
Abundant moisture will be in place with precipitable water values
1.5 to 2 inches across our area, with low-level moisture influx from
the Gulf of Mexico, and mid-high level moisture incorporated into
the system from the eastern Pacific.
In the Saturday night to Monday time frame, several disturbances
aloft are progged to rotate around the eastern periphery of the
upper low and into the western half of Texas. With this setup,
anticipate several rounds of showers and thunderstorms with
increased coverage and heavy rainfall. In addition, the slow-
moving frontal boundary will provide an additional focus for heavy
rain. Rain chances will ramp up Saturday night and continue
through Sunday night, with likely PoPs extending through Monday.
From Saturday night through Monday, widespread rainfall totals of
2-4 inches will be likely, with locally higher amounts possible.
While our area can take some rain initially, expect multiple rounds
of convection to saturate the ground and lead to excessive runoff/
flooding. A flash flood threat will also exist. We are monitoring
this developing wet weather situation closely, and a Flash Flood
Watch may be issued if the next set of models continue to show this
setup for our area.
Temperatures will be much cooler at the beginning of the week,
especially on Monday. Rain chances will be lower, but still present
in parts of our area Tuesday and Wednesday. Later in the week,
temperatures are expected to warm back into the lower to mid 80s for
highs (Thursday and Friday), when an upper level ridge tries to
build back into our area.
19
.PRELIMINARY POINT TEMPS/POPS...
Abilene 71 88 69 77 / 20 50 70 80
San Angelo 73 92 71 78 / 10 40 70 80
Junction 73 91 72 82 / 20 30 60 70
Brownwood 71 89 71 80 / 20 40 50 80
Sweetwater 69 88 69 73 / 20 60 80 90
Ozona 72 89 70 78 / 10 40 70 80
&&
.SJT Watches/Warnings/Advisories...
None.
&&
$$