Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/14/17
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
815 PM CDT Wed Sep 13 2017
.UPDATE...
Issued at 813 PM CDT Wed Sep 13 2017
Forecast is in fine shape so no major changes. Smoke looks like it
will hang around the northern CWA through at least Thursday
morning before hopefully mixing out as low pressure heads east
across the region. Isolated showers out west may make their way
into the east late. Temperatures look good.
&&
.SHORT TERM...(This Evening through Thursday Afternoon)
Issued at 338 PM CDT Wed Sep 13 2017
An upper ridge over the central CONUS has led to continued above
normal temperatures over much of the region today under a sunny
sky. As of 2pm, temperatures have risen into the upper 80s and
lower 90s, except over north central South Dakota, where thick
smoke has limited temperatures. At KMBG, temperatures have
struggled to rise into the lower 80s and visibilities have been
steady in the 1.5-1.75mi range throughout the day. The HRRR smoke
model and NWS Air Quality forecast have both picked up on the
near surface smoke well today. Using those tools as a guide, have
expanded the smoke into the morning hours tomorrow since winds
will be light and don`t expect much change in the conditions.
The light winds that are over the area are being caused by a
broad area of low pressure in the lee of the Rockies in WY/CO and
the dissipating cold front stretches from northeast to southwest
across SD and to the main low. As we have a series of shortwaves
move over the area through Friday, the surface low will gradually
shift east through southern SD tonight through Thursday. The
first wave is currently moving into the western Dakotas and are
already seeing some showers in southwest ND. Expect these high
based showers to move into central SD later this evening and
likely dissipate through the overnight hours. Lapse rate above
the cloud bases are very weak (only 5.5-6 C/km), so not expecting
much for thunder. If there are any stronger cells, the dry air
below 12kft may lead to gusty winds. Also, some hints in the high
resolution models (ESRL HRRR especially) for the potential for
heat bursts again tonight as the showers/storms weaken or
dissipate.
For tomorrow, there will likely still be isolated showers
continuing through the day, but largely over the northern part of
the CWA (where the best moisture above 600mb is located) as a
couple weak waves move through. At this point, thinking the best
chances will be in SE ND where the moisture/forcing are
co-located. Still expect a surface trough to be nearly stationary
over portions of the southeast CWA, although models still vary on
the location depending on the strength of a weak llvl jet tonight
over eastern SD. Confidence is very low at this time, but could
see some development along that trough where there is an increase
in convergence and some moisture pooling. Hi-res models haven`t
been too enthused with development at this point, so have shown
limited PoPs during the afternoon. If something does develop,
there would be enough shear/instability to produce a strong
thunderstorm.
.LONG TERM...(Thursday Evening through Wednesday)
Issued at 338 PM CDT Wed Sep 13 2017
The models agree real well with the upper level pattern from
Thursday night through Wednesday next week. The main issue during
this period will be the mean upper level troughing over the western
U.S. At this time, the most significant short wave trough to come
out of this western trough will be Thursday night through Friday
night. The models all agree that most of our CWA will have good
chances of showers with some thunderstorms southeast in the CWA. The
main upper low pressure trough out west will then kick out across
our region later Friday night through Saturday evening bringing more
chances of rainfall. One more quick moving short wave trough from
the west will bring more chances of showers/storms for Sunday night
into Monday. The models then show another large upper low pressure
trough digging into the southwest U.S. with upper level heights
building over our region from Monday into the middle of next week.
Temperatures will be cooling down from Thursday into Friday and
remaining below normal through the weekend as we remain on the north
side of the surface cold front with north winds. Highs should be
only in the 60s for both Saturday and Sunday. Temperatures are
expected to then warm up from Monday into Wednesday as winds become
south with upper level heights rising. Temperatures will be back in
the 70s and 80s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 619 PM CDT Wed Sep 13 2017
Smoke will continue to affect vsbys around KABR/KMBG through the
night. KPIR/KATY should be mostly unaffected. The smoke should
begin to mix out on Thursday as a frontal boundary moves across
the region.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...TDK
SHORT TERM...SRF
LONG TERM...Mohr
AVIATION...TDK
Area Forecast Discussion
National Weather Service La Crosse WI
636 PM CDT Wed Sep 13 2017
.SHORT TERM...(Tonight through Thursday)
Issued at 211 PM CDT Wed Sep 13 2017
A surface ridge over the eastern part of the forecast area will
continue to shift off to the east through tonight, with low pressure
forming in the Dakotas and beginning to move eastward. Models are in
good agreement with the pressure gradient tightening ahead of this
low, bringing increasing southerly winds to the area for Thursday.
Winds look to remain strong enough aloft over most of the area
tonight to suppress widespread valley fog formation, but could see a
bit of fog in central and southwest Wisconsin where winds remain a
bit lighter. That said, the RAP has been trending less windy aloft,
so could see a bit of stratus in the valleys by Thursday morning.
Otherwise, the main forecast concern for this period will be high
temperatures on Thursday. The previously mentioned increasing
southerly flow will bring 925 mb temperatures ranging from 22 to 28
C to the forecast area. This will lead to high temperatures in the
mid 80s for most locations, with a few areas in far western portions
of the forecast area approaching 90. Any precipitation chances
during this period look to stay well to the northwest along a
surface boundary.
.LONG TERM...(Thursday Night through Wednesday)
Issued at 211 PM CDT Wed Sep 13 2017
13.12Z Models showing a weak mid-level trough ejecting northeast out
of the Plains Thursday night along with some weak 850-700mb moisture
transport. This should be enough to fuel a lower-end chance of
elevated/altocumulus showers across portions of MN and IA into
western WI.
Friday is looking unseasonably warm and capped off as we get solidly
into the warm sector of deepening low pressure moving out of the
Central Plains into MN. Other than a few mid/high level clouds,
expecting full mixing in southerly flow with 925mb temperatures
climbing into the 24-27C range. This is expected to push highs in
the middle 80s to near 90 across the area.
Shower/thunderstorm chances will be seen Saturday into Sunday
morning as a cold front slowly makes its way across the region.
Severe threat appears minimal at this time as the front comes
through Saturday night with diminishing CAPE and fairly weak shear.
Will continue to monitor frontal timing. Pre-cold frontal high
temperatures still look a bit warm with readings in the 80s. Post-
frontal temperatures Sunday look a bit more seasonable with highs
topping off in the upper 60s to the middle 70s.
For Monday through Wednesday...southwest flow aloft will push a
couple systems across the area for occasional shower/thunderstorm
chances. Otherwise, temperatures are expected to be at or a few
degrees above seasonal normals.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 636 PM CDT Wed Sep 13 2017
VFR conditions will continue into Thursday evening as upper level
high pressure holds across the region. Outside of some passing
cirrus at times, skies should be mainly clear, with lighter winds
tonight increasing from the south at 10-15 knots on Thursday. Some
afternoon gusts to around 20 knots are possible at RST.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...CJA
LONG TERM....DAS
AVIATION...Lawrence
Area Forecast Discussion
National Weather Service Bismarck ND
943 PM CDT Wed Sep 13 2017
.UPDATE...
Issued at 938 PM CDT Wed Sep 13 2017
Scattered thunderstorms are forming in a very limited area
associated with the warm/cold front and surface low just east of
Hettinger this evening. Ingredients for convection continue to be
weak with limited CAPE and Shear. Will keep an area of
thunderstorms tonight along the path of this surface low across
south central North Dakota. Adjusted POPs a bit to follow the Lows
track tonight.
UPDATE Issued at 631 PM CDT Wed Sep 13 2017
The smoke continues to remain as issue this evening. However the
trend has been for improving conditions across the northwest and
if this trend continues there may be much better smoke conditions
on Thursday. Otherwise, scattered light showers remain over the
west with a few isolated lightning strikes southwest.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 302 PM CDT Wed Sep 13 2017
Continued smoke through tonight into Thursday morning
highlights the short term forecast.
Widespread smoke with reduced visibility is favored to continue
tonight into Thursday morning. Surface smoke is expected to
decrease through the day on Thursday with an airmass exchange via
breezy northerly winds. This is favored by the 12 UTC experimental
HRRR surface smoke forecast, and additional experimental surface
smoke forecasts available at www.airquality.weather.gov.
A series of rapidly propagating impulses will continue the
scattered rain shower and isolated thunderstorm threat through
the night that is currently across the west this afternoon. Severe
weather is not expected.
.LONG TERM...(Thursday night through Wednesday)
Issued at 302 PM CDT Wed Sep 13 2017
Much cooler temperatures, and widespread rainfall Friday into
Saturday highlight the extended forecast.
The 12 UTC global suites continue to remain in good agreement on
widespread rainfall developing Thursday night and continuing
Friday across western and central North Dakota north of the
surface low across Nebraska as the first of two potent waves
propagate across the Northern Plains. A second and stronger wave
will impact the area on Saturday, however, a dry slot is favored
to impact the southwest and south central limiting rainfall
chances for these areas. Overall, widespread one to two inches of
rain are possible for much of the area, with locally higher
amounts along an axis from the southwest into north central.
Widespread highs in the 50s are expected Friday and Saturday. As
cool surface high pressure builds across the area Saturday night
into Sunday, frost may be possible.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 620 PM CDT Wed Sep 13 2017
Smoke will continue through tonight into Thursday morning across
most of western and central North Dakota, with MVFR/IFR visibility
confined mainly to south central North Dakota where the smoke
will be thickest. Surface smoke is expected to decrease through
the day Thursday as surface winds turn north to north- northeast.
Isolated showers and thunderstorms are possible west this
afternoon, with the threat continuing through the night west and
central. With low confidence of timing left the mention of
thunderstorms out of the TAFS at this time.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...WAA
SHORT TERM...PA
LONG TERM...PA
AVIATION...WAA
Area Forecast Discussion
National Weather Service Denver/Boulder CO
800 PM MDT Wed Sep 13 2017
.UPDATE...
Issued at 800 PM MDT Wed Sep 13 2017
Isolated showers and thunderstorms remain over the area. Expect
them to decrease and end with in the next two hours. Adjusted the
forecast to remove pops a couple hours earlier. Otherwise,
forecast is on track.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 327 PM MDT Wed Sep 13 2017
Latest GOES-16 mesoscale 1 min data combined with radar imagery
has shown that convection has been relatively easy to initiate
today across the Palmer Divide and Front Range mountains and
foothills, but having a fairly hard time sustaining itself across
the lower elevations. With inverted V soundings and surface
dewpoints in the 30s, convection should continue to be on the weak
side of the spectrum the rest of today. The exception may be our
northern counties Larimer/Weld/Morgan/Logan/Phillips/Sedgwick
where slightly better low-level moisture and higher precipitable
water exists. Have increased PoPs this afternoon across our
northern counties based on latest observational trends and HRRR
guidance. Early convection across Weld/Morgan County has already
generated a outflow boundary that should continue to be a focus
for more showers and thunderstorms the rest of the afternoon. In
general, storms will be capable of gusty winds and cloud to ground
lightning until the weaken and/of move into Kansas by about 10
PM. Expect it to be dry area wide after 10 PM.
Tonight a cirrus shield from upstream convection should keep
overnight temperatures warm, with lows near 60 across the I-25
metro corridor, upper 50s rest of the Plains, and generally 40s in
the mountains. All quite warm for mid-September standards. During
the day Thursday a strong trough moves into the Great Basin and
Colorado is under weak southwest flow, and thickness values
decrease across the state. High temperatures should be 3-7 degF
cooler than today area-wide. By Thursday afternoon weak synoptic
lift spreads over the state, and combined with a modest increase
in total precipitable water values (0.80-1.00" Plains, 0.5-0.6
mountains), shower and thunderstorm should be slightly more
numerous Thursday afternoon relative to Wednesday but still not
enough for a free watering of lawns and gardens in most areas
across the Plains. Mountains and foothills, as typical, should
have better shower and thunderstorm coverage. Vertical wind shear
despite southwest flow is still pretty weak, while instability
will again be limited to around 500 J/kg across the Plains. Thus,
main impacts with the afternoon storm will be gusty winds to 35
mph and cloud-to-ground lightning.
.LONG TERM...(Thursday night through Wednesday)
Issued at 327 PM MDT Wed Sep 13 2017
Longwave trough will remain upstream over the west through the
period. One shortwave trough will kick out of the trough in the
Friday/Saturday time frame, with another shortwave deepening the
trough to our west early next week. On a smaller scale, a lesser
wave will produce some lift ahead of the trough and bring up some
mid level moisture Thursday night. This should be the best chance
of precipitation for most of the area with enhanced convective
activity. CAPES will be low however, so not expecting much
strength to the storms. With a bit more moisture there could be
more rain, but gusty winds are probably still the main threat.
There will be a bit of a break before the bigger piece of the
trough comes through. There is some disagreement on the timing of
this, sometime late Friday or early Saturday. This trough will
bring some cooling aloft and drag a significant cold front across
the plains, but there is a sharp south edge to the mid level
moisture that will be over our mountains or perhaps near the
Wyoming border. Lower confidence on the details, but typically in
these situations the cold front will roll right along without much
regard for the timing of the higher trough. If the front comes
early enough it could hold back highs on Friday with falling
temperatures late in the afternoon. It looks like there will be
enough cooling for some snow in the higher mountains where the
moisture is. Snow level should stay above 9000 feet and probably
above 10 thousand. At any rate, amounts should be light and
temperatures warm, so not expecting any accumulation at or below
pass elevations. I did try to smooth out the tight gradient in
PoPs in the models in case the moisture winds up clipping the I-70
corridor.
Saturday will be cooler and may have some stratus in the morning.
There is also some discrepancy about how dry the new air will be.
Drier solutions would have patchy stratus in the morning, then
clearing. The moister solutions would have enough for some diurnal
convection mainly over the mountains.
For Sunday into the early part of next week, recovering
temperatures as dry southwest flow aloft develops downstream from
the reloading trough. It could get to be quite dry, warm and
breezy Monday or Tuesday which could raise the fire danger. Fuels
have dried out in most areas over the last several weeks, so we
could be getting closer to Red Flag conditions. Most model runs
are keeping the large trough west of us with some kind of
shortwave kicking out of it Tuesday/Wednesday. Most solutions are
fairly dry, and could have a day of stronger winds in this
pattern. There are some outliers that just keep us warm through
Wednesday, or move the trough over us for stronger cooling and a
bit better chance of showers. But most likely, it will just be a
little cooler by the middle of the week after a couple of quite
warm and dry days.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 800 PM MDT Wed Sep 13 2017
Northeast winds will turn clockwise and become southerly by 06Z. The
threat for storms has ended at the Denver airports. Another round of
high based showers and thunderstorms is expected Thursday afternoon.
Main threat will be wind shifts from the convection.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Meier
SHORT TERM...Schlatter
LONG TERM...Gimmestad
AVIATION...Meier
Area Forecast Discussion...Updated
National Weather Service Billings MT
848 PM MDT Wed Sep 13 2017
.UPDATE...
Convective outflows have grabbed onto the Canadian cold front this
evening. The leading edge is located from Hysham to Hardin and
pushing eastward. Broad area of showers and isolated embedded
thunderstorms has filled in behind the front bringing 0.05 to 0.15
inches of rain over a wide area. Temperatures ahead of the front
are still in the mid 70s, with 50s and 60s on the backside.
Billings airport recorded the strongest gust of the evening at 52
mph as the front moved through, but other gusts in the 40s have
been reported. This initial batch of precipitation will continue
to move east overnight and will lose some of its punch as it does
so. The main frontogenesis precipitation band will develop to the
north of our area late tonight and sink into western zones around
sunrise. Kept low pops in for the night in general, with higher
but diminishing chances along initial frontal boundary currently
over central zones. Mention of thunderstorms will fade overnight
from west to east. Latest HRRR model solution indicates smoke will
be slow to clear as a broad area has gotten stuck under the
frontal inversion that will press into the area from the north
overnight. So the improvements brought by the evening rainfall may
be shortlived in some areas. Expect gradual improvement over the
next 24 hours as the colder wetter airmass will diminish fire
intensity allowing improvement across the region. Chambers
&&
.SHORT TERM...valid for Thu and Fri...
Showers and thunderstorms were found across the area this
afternoon as energy and moisture was streaming in from the
west and southwest. Expect shower/thunderstorm activity to
continue into the evening. Models have remained consistent in
bringing a significant pattern change to the area as a low
pressure system moves into the region ushering in much cooler
temperatures and widespread precipitation beginning Thursday.
Showers will increase across the area Thursday as the low pressure
system moves into the region and north to northeast upslope flow
develops. A few embedded thunderstorms are possible across
southern areas with instability present. The cool and wet pattern
will continue Friday into Saturday as the low pressure system
lifts through the region and upslope flow remains in place
bringing periods of showers to the area. Snow levels will drop
Thursday night into Friday as temperatures cool aloft.
Accumulating snowfall is possible above 7,000 feet.
When all is said and done, total rainfall numbers will range from
1 to 2 inches, with higher totals possible in upslope prone areas
along the foothills/mountains. Snowfall totals of 6 to 12 inches,
with locally higher amounts are possible for the Crazy,
Beartooth/Absaroka, and Bighorn Mountains. Have issued Winter
Storm Watches for these zones from Thursday evening through
Saturday afternoon. Slushy snow accumulations of an inch or two
are not out of the question for foothill locations Friday
night/Saturday morning with temperatures in the 30s.
High temperatures will range from the 50s west, to near 70 east on
Thursday, with 40s and 50s for highs expected on Friday and
Saturday (close to 30 degrees below climatology for this time of
year). Low temperatures will range from the 40s and 50s tonight,
to the 30s and 40s through the rest of the short term. Coldest
nights look to be Friday night and Saturday night. STP
.LONG TERM...valid for Sat...Sun...Mon...Tue...Wed...
Weak upper ridging builds in for Sunday as the low pressure system
exits the region, giving a dry and warmer day to the area with
high temperatures generally in the 60s.
Next upper low/trough moves southeastward on Sunday so that it is
over the Pacific Northwest by Monday. The GFS brings the low over
the Northern Rockies during the middle of the week. ECMWF
ensemble mean generally agrees with this solution and even keeps
the trough over the Rockies through the end of the week. What this
means is that the potential is there for another rain/mountain
snow event next week. Areas west of Billings could see showers as
early as Monday afternoon. A chance of showers then expands
eastward for much of the rest of the CWA Tuesday and Wednesday.
Details involving more precise timing and precipitation amounts
are uncertain at this time. High temperatures should generally be
in the 60s to lower 70s Monday-Wednesday. RMS
&&
.AVIATION...
Scattered showers and thundestorms should continue through
tonight. Local MVFR conditions are possible in the heavier
showers. Patchy smoke will also reduce visibility at times to MVFR
this evening. Otherwise, VFR will prevail. Mountains will be
obscured in showers and thundestorms. AAG/RMS
&&
.PRELIMINARY POINT TEMP/POPS...
Thu Fri Sat Sun Mon Tue Wed
-----------------------------------------------------------
BIL 053/059 043/046 038/052 037/066 044/073 049/067 043/069
38/W +9/R 76/T 20/U 01/B 32/W 43/W
LVM 047/058 037/042 031/049 027/062 035/069 040/064 034/065
38/T +9/O 87/T 10/B 12/T 55/W 33/W
HDN 051/067 043/049 037/053 033/070 040/077 045/069 041/072
66/W +9/R 76/T 20/U 01/U 12/W 44/W
MLS 054/067 045/050 038/053 034/069 042/077 049/073 044/072
53/W ++/R 66/W 20/U 20/U 10/N 44/W
4BQ 053/074 046/053 037/053 034/069 041/077 050/076 043/073
42/T 9+/R 55/W 20/U 30/U 00/B 22/W
BHK 052/070 046/051 038/051 035/067 041/075 049/074 044/072
32/W ++/R 76/W 20/U 20/U 00/N 22/W
SHR 050/070 042/048 034/053 029/066 038/076 044/070 039/067
56/T 99/R 76/T 20/U 10/U 00/B 44/W
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch in effect from Thursday evening through
Saturday afternoon FOR ZONES 67-68.
WY...Winter Storm Watch in effect from late Thursday night through
Saturday afternoon FOR ZONE 98.
&&
$$
weather.gov/billings
Area Forecast Discussion
National Weather Service Indianapolis IN
1022 PM EDT Wed Sep 13 2017
.UPDATE...
The AVIATION section has been updated below.
&&
.SYNOPSIS...
Issued at 210 PM EDT Wed Sep 13 2017
A high pressure system will gradually develop over the eastern
United States as the remnants of Hurricane Irma dissipate. By late
Friday this system will cover most of the nation east of the
Mississippi. A weak cold front should pass Indiana Monday. After
that expect high pressure to reestablish itself from our state to
the deep south.
&&
.NEAR TERM (Rest of Tonight and Thursday)...
Issued at 941 PM EDT Wed Sep 13 2017
Forecast PoPs are on track with higher PoPs east and lower PoPs west
matching radar trends well. Only made some minor tweaks to PoPs.
Main question was fog potential. Some model guidance is suggesting
widespread dense fog, but am not sure that this will occur with
clouds not breaking up much and stratus being favored with some
mixing occurring above the surface.
Have added areas of fog west where higher potential exists for some
breaks in the clouds overnight with patchy fog east. Where fog does
form it could become dense.
Temperatures look good so no significant changes made.
Previous discussion follows...
The forecast problem is how fast rain will end.
There is overall model agreement about showers slowly tapering off
as the remnants of Irma pull away, and that we should see clearing
by late tomorrow. Exactly how fast this happens is different in
different models.
Consensus POPs often works well in such situations. However simple
consensus seems underdone considering both what we see on satellite
and what the HRRR shows. The best approach is to start at a higher
basis then consensus. but to keep overall trends.
This results in likely POPs in the eastern part of the area
overnight, with at least a chance everywhere. POPs should dwindle
to just a slight chance in the east by Thursday morning.
There is good uniformity between the models in features that will
drive temperatures, especially since everything points to mostly
cloudy skies tonight. Consensus will be used, with expected errors
of 3 degrees or less.
&&
.SHORT TERM (Thursday night through Saturday)...
Issued at 210 PM EDT Wed Sep 13 2017
There is good model agreement about high pressure centered over
the Appalachians dominating the weather.
That translates into good agreement Indiana will have mostly clear
skies with a warming trend. Consensus temperatures should work
well. Expect errors mostly less than 3 degrees.
&&
.LONG TERM /Saturday Night through Wednesday/...
Issued at 210 PM EDT Wed Sep 13 2017
Starting the period with a ridge of high pressure that extends
from the northwest Gulf of Mexico north-northeast into the lower
Great Lakes. This will be reflected at the surface with high
pressure across the area which will control the weather over the
weekend with temperatures above normal,low-mid 80s), during the
day and low to mid 60s at night.
Confidence:High
At the start of next week, large mid/upper level trough is
expected to be from a low over southeast Alberta southwest through
CA. Southwest flow aloft will gradually push the ridge of high
pressure over our area eastward. Timing seems questionable at
this time as the model blend brings in a slight chance for rain as
early as Sunday night and Monday where the GFS holds it back
until more midweek. It seems like the old ECMWF is the faster one
bringing the precipitation in like the model blend. Temperatures
are forecast to be just above normal going into mid week.
Confidence: Low on timing of precipitation, moderate on
temperatures.
&&
.AVIATION (Discussion for the 140300Z TAF Update)...
Issued at 1022 PM EDT Wed Sep 13 2017
Looking at nearby observations, not sure that the ceilings below
2000FT at KIND will be predominant yet, so kept ceilings above
2000FT for a couple of more hours.
Previous discussion follows...
IFR or lower conditions expected overnight. Conditions will improve
to VFR Thursday afternoon.
Conditions may vary between VFR and MVFR early in the period before
settling down to IFR or even lower overnight. At the moment, believe
that stratus will be the primary issue overnight so kept
visibilities in MVFR category for most sites.
However, there is the potential that the stratus may not form as
much as expected, allowing visibilities to fall to a half mile or
less as some model guidance is suggesting. Will have to keep an eye
on this. Thus confidence is only medium at best for visibility and
for how low ceilings will get.
Fog/stratus will gradually burn off Thursday, allowing VFR
conditions to return during the afternoon. Winds will remain light.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...JK
NEAR TERM...JK/50
SHORT TERM...JK
LONG TERM....DM
AVIATION...50
Area Forecast Discussion
National Weather Service Medford OR
843 PM PDT Wed Sep 13 2017
.DISCUSSION...Thunderstorms that developed this afternoon/early
this evening east of Mount Shasta and in Modoc/southern Lake
Counties have ended and it should be dry in those areas the rest
of tonight. These storms were able to produce about 65-70 cloud to
ground strikes, most of which occurred in SE Siskiyou County east
of Mount Shasta.
A frontal system offshore will move onshore overnight, then push
through area on Thursday. This will be mostly a dry front, but
latest high resolution models are indicating there could be
isolated showers along the north coast and into the Umpqua Valley
early Thursday morning. It is likely there will be some radar
returns associated with the front Thursday morning, but models are
indicating a very dry layer between 850 and 700 mb, so it will be
difficult to get anything to reach the ground. Have indicated a
slight chance of showers, but probably nothing measurable in the
morning. By afternoon, the NAM12 is fastest moving the front east
of the Cascades and while it does generate isolated showers,
instability appears negligible for thunderstorms. Other guidance,
however, is slower and allows for some instability to develop
again across SE Siskiyou County over to southern Modoc County in
the afternoon, before pushing SE away from the area during the
early evening. The HRRR guidance is hinting at potential
thunderstorm development, so have included a slight chance in
those areas. Expect some gusty north to northwest winds for most
areas Thursday afternoon and evening. -Spilde
&&
.AVIATION...14/00Z TAF CYCLE...
Isolated showers this evening east of Mount Shasta, Modoc and
southern Lake Counties have ended. Local MVFR to IFR conditions
are expected in rainfall with these storms, and gusty outflow
winds are possible along with lightning. Otherwise, it will be VFR
and a bit breezy this afternoon and evening. With a dry cold
front moving through today, we`ve seen low level winds shift
westerly to northwesterly farther aloft. This will bring some
smoke from the Chetco Bar near TAF site MFR later tonight, but
will not drop visibilities below MVFR.
As for along the coast, MVFR to IFR is expected later this morning
with slightly on shore winds. Most guidance is suggesting a drop
in visibilities around 12z near OTH. -BTL/Smith
&&
.MARINE...Updated 400 PM PDT Wednesday 13 September 2017...A thermal
trough pattern will persist until Saturday, producing periods of
gusty winds and steep seas over the coastal waters...along with
gales and very steep seas Wednesday night beyond 2 NM from shore and
south of Gold Beach. The thermal trough will weaken... however small
craft conditions will continue through Saturday.
Eventually, a mature fall storm system will move through the waters
producing steep north west swells with wave heights around 10 to 12
feet on Monday. Wind wave heights are not expected to be too strong
hence why were forecasting steep versus very steep seas.
-Smith
&&
.FIRE WEATHER...Updated 845 PM PDT Wednesday, 13 September
2017...The showers and thunderstorms that were east of Mount
Shasta, over Modoc and southern Lake Counties have dissipated and
it should be dry there the rest of the night. The storms that did
develop were able to produce about 65-70 cloud to ground strikes,
most of which occurred in FWZ284 in SE Siskiyou County.
Very dry air moving across the upper slopes and ridges, mainly above
6,000 feet tonight through Thursday morning, is likely to result in
active burning continuing on existing fires at higher elevations.
The NAM12 guidance indicates single digit RHs above 6kft Thursday
morning, while the GFS indicate lower 20s. Have adjusted the
forecast to indicate downward hourly RH trends in the Cascades
overnight, with minimums above 6kft Thursday morning in the teens.
Some guidance, such as the METBC, indicate low ridge top RHs
reaching other mountain areas, as well, so have lowered the upper
slope and ridge RHs accordingly. This dry air is associated with a
mostly dry cold front that will move across the forecast area
tonight through Thursday. Northwest winds will become gusty Thursday
afternoon and evening.
Light east winds and another night of moderate to poor recoveries
are expected Friday night into Saturday morning, likely of most
concern and least recovery in western Siskiyou County and Curry
County.
Southwest winds will increase Sunday ahead of a major trough of low
pressure and could gust 30 to 40 mph over SE sections of the area,
especially in Modoc and Lake Counties. This trough is expected to
bring wetting rainfall from the Oregon Cascades and Marble Mountains
westward Sunday night through Tuesday, with showers across the east
side. Snow levels are likely to fall to near 6kft. Of note, the 8-14
day forecast from CPC and the 16 member ensemble CFSv2 continues to
indicate cooler and wetter conditions as compared to what is normal
for this time of the year. BTL
&&
.PREV DISCUSSION... /Issued 511 PM PDT Wed Sep 13 2017/
DISCUSSION...The cutoff upper low that brought thunderstorms to
portions of northern California and Lake County is just off the
coast, south of the Bay area in California. At the same time an
upper trough near southern Vancouver Island is in the beginning
stages of digging south. This will put the squeeze play on the cut
off upper low and will push it eastward into southern Nevada in the
next 18-24 hours. Isolated thunderstorms have developed near
Medicine Peak and most of the cumulus development has been in Modoc
eastern Klamath and southern Lake County. The latest SPC mesoscale
analysis also shows most of the instability in the above mentioned
areas which makes sense. In addition, the models hint at marginal
instability into early this evening. Given the above reasoning.
We`ll put in isolated thunderstorms in the above mentioned areas
through early this evening.
Tonight will be dry and cooler as the upper trough moves south
towards our area. A few isolated locations in northern Klamath and
Lake county could get close to freezing towards daybreak Thursday,
but much will depend on the amount of cloud cover.
An upper trough will dig south over our area Thursday. This upper
trough is significant enough that it will bring in much cooler air
(probably the coolest we have seen a few months) will move into our
area. The trajectory of the upper trough is one that is not normally
favorable for precipitation, but one that will bring cooler
temperatures and gusty winds, especially along and east of the
Cascades. Thursday night will be chilly with less cloud cover east
of the Cascades and there`s a better chance for near or below
freezing temperatures, especially in northern Lake and Klamath
Counties. Therefore we`ll issue a freeze watch for these areas.
Please see NPWMFR for more details.
Friday will be dry and milder for most inland locations and weak
shortwave ridging builds in. At the surface a thermal trough will
develop along the coast with clear skies over most areas. A weak
upper trough will move through the area Saturday, but it won`t have
any impact on our weather except for increasing mid level clouds and
slightly cooler temperatures.
The models are in pretty good agreement and continue to show a
significant cooldown with increasing precipitation starting as
early as Sunday evening at the coast, then inland locations Sunday
night and lasting into at least the first half of next week.
Confidence is high enough for both to happen and have adjusted pops
significantly higher. There are some tining differences with the
first wet front Sunday evening. For example, the ECMWF is faster
with arrival of precipitation and the GFS slower at the coast. It`s
possible the GFS solution is slow, so we`ll lean towards the faster
ECMWF for now and make further adjustments as we get closer to
Sunday.
The front will move inland through the area Monday, followed by a
strong upper low for this time of the year. This upper low will user
in the coolest air mass so far this season along with max
temperatures averaging 10-15 degrees below normal and scattered
showers over most locations Monday through Tuesday night. With the
much cooler air mass comes lower snow levels. Right now, the
thinking is snow levels will drop down to near 6,000 feet, so it`s
possible the mountains could see wet snow Monday night into Tuesday
night. Right now we don`t think there will be any accumulation, but
could not rule out a trace of slush on the ground in heavier showers
at night. In addition, the pattern is also favorable for moderate to
heavy showers in the afternoon and evening hours. It`s still too far
out there to detail where the heavier showers will be, but it will
bear close watching as it could effectively put a huge dent into the
existing fires in our area.
There`s some question as to how quick the upper trough will exit out
of our area next Wednesday. However the models show a northerly
flow aloft over our area which typically results in drier conditions
over our area. It remains to be seen how this will evolve in the
days to come. -Petrucelli
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Watch from late Thursday night through Friday morning for
ORZ029>031.
CA...None.
Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Thursday
for PZZ350-370.
Small Craft Advisory until 5 PM PDT Friday for PZZ356-376.
Gale Warning until 5 AM PDT Thursday for PZZ356-376.
$$
MAS/MAP/BTL/CZS
Area Forecast Discussion
National Weather Service Pueblo CO
259 PM MDT Wed Sep 13 2017
.SHORT TERM...(This evening through Thursday)
Issued at 239 PM MDT Wed Sep 13 2017
A weather disturbance will continue moving eastward acrs the area
thru the evening, helping to kick off some showers and
thunderstorms. The HRRR shows an area of pcpn heading eastward acrs
the plains as the disturbance moves east, late this afternoon
through about 05Z.
Late tonight another weak disturbance is forecast to enter southwest
CO, which could lead to some late night and early Thu morning pcpn
chances over the Continental Divide. On Thu, an upper low is
forecast to move from srn portions of CA, acrs srn NV and into srn
UT. Ahead of this system, moisture will increase over the area and
scattered shower/tstm are expected over the mtns and high valleys in
the late morning and afternoon hours, with possibly some isolated
storms spreading out over the I-25 corridor and eastern Las Animas
county by late afternoon. Temps on Thu will be above average again,
with highs mostly in the upper 80s to mid 90s across the plains, but
a little cooler in northern portions of El Paso county, and in the
70s in the high valley locations.
.LONG TERM...(Thursday night through Wednesday)
Issued at 239 PM MDT Wed Sep 13 2017
No changes to the forecast thinking through the extended period. A
big pattern change looks to occur by Friday, with the monsoonal
ridge shifting east, and several upper disturbances dropping south
out of the Pacific Northwest, much more like a fall or winter type
pattern across the western states.
Thursday night...the first upper shortwave trough will be moving
across Colorado Thursday night. Expect ongoing widespread showers
and thunderstorms across the mountains, spreading east across the
Plains through the overnight hours. Locally heavy rainfall will be
possible with stronger storms. Expect this activity to push east
into the Central Plains by late Thursday night into Friday
morning.
Friday through Saturday...broad southwest flow will set up across
Colorado with troughing over the western states. Energy will pass
by well to the north leaving most of Southern Colorado dry both
Friday and Saturday. An isolated shower or thunderstorm may be
possible over the Central Mountains, but do not expect them to be
widespread or last more than the afternoon and early evening
hours. Friday will be hot with highs in the upper 80s to lower 90s
across the Plains. A cold front from the system passing to the
north will bring cooler temperature to the area on Saturday with
highs in the upper 70s to lower 80s.
Sunday through Tuesday...the next upper disturbance will move
across Colorado by Sunday bringing with it another round of
isolated to scattered showers and thunderstorms over the Central
Mountains, northeast across the Palmer Divide into northeast
Colorado. Meanwhile, the GFS brings moisture associated with a
tropical disturbance from the East Pacific north across New
Mexico. This may bring showers and thunderstorms to our southern
border as it moves northeast into central Kansas Monday and
Tuesday. The ECMWF does not have this tropical disturbance early
next week, and keeps shower and thunderstorm activity pretty
isolated to scattered in nature over the mountain areas, while the
Plains remain dry and warm.
Wednesday...a strong storm system is forecast to drop south over
the Great Basin by mid week. This would increase shower and
thunderstorm activity over the mountains. Current temperature
profiles also indicate there could be early season snowfall on the
high Colorado peaks as well. Mozley
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 239 PM MDT Wed Sep 13 2017
VFR conditions are expected tonight through Thu at KCOS, KPUB and
KALS. There will be the possibility of showers/tstms at KCOS and
KPUB thru mainly the early evening hours. KALS could see a shower
or tstm but chances are lower than at KCOS and KPUB. Thu afternoon,
there will be chances for showers/tstms at KALS, and possibly at
KCOS by late afternoon.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...28
LONG TERM...MOZLEY
AVIATION...28
Area Forecast Discussion
National Weather Service Blacksburg VA
1135 PM EDT Wed Sep 13 2017
.SYNOPSIS...
Low pressure will track into Pennsylvania by Thursday morning.
High pressure will cover much of the Mid Atlantic region for
Thursday night and Friday. A cold front will approach the region
from the northwest on Monday and Tuesday.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 1130 PM EDT Wednesday...
Keeping current forecast similar to previous with
isolated/scattered showers in two distinct areas early per radar
depiction. One over southside VA into the NC piedmont, and the
other over WV into the Alleghany, south toward the NC mountains.
Overall light amounts expected. Clouds will be plentiful
overnight which should limit fog, though some of the higher-res
models show some clearing after 5am, and if this occurs, fog
will become dense in spots, but overall confidence is low in
this occurring, per upstream satellite showing clouds stretched
all the way back into northern Alabama.
Previous discussion from early evening...
Mid-level height falls associated with weakening/filling upper
low over northeast KY continue to overspread the region.
Regional radar and METARs show intervals of showers still to our
west and southwest in eastern KY into eastern TN. Finer-
resolution guidance has slowed a bit on the eastern advancement
of the showers into areas west of the Blue Ridge, opting for a
mid to late evening start time. HRRR and 3-km NAM also are
keying on development of steady light showers along subtle
convergence axis across the Southside of VA into the north-
central NC Piedmont after midnight. Outside of these areas, look
for at least an increase in clouds areawide - though a slower
increase in our northeastern VA counties. No changes to lows
attm - in the middle 50s to lower/mid 60s.
Previous near-term discussion issued at 215 PM Wednesday
follows...
Guidance brings the filling upper low out of the Tennessee Valley
tonight, with the short wave on the southern and eastern side of the
low reaching southwest Virginia, Northwest North Carolina, and
southeast West Virginia close to 00Z/8PM. Best probability of
precipitation remains on western slopes of the Appalachians. Will
also be adding a chance of rain tonight into the piedmont of
Virginia and North Carolina, which is another area that will have
moisture increasing from the surface through mid levels.
Several of the ensembles showing only a small rise in
temperatures on Thursday. Relatively coolest 850MB
temperatures,around +10, will be over the Ohio Valley 12Z/8AM
Thursday morning.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 215 PM EDT Wednesday...
Expecting high pressure and lighter winds on Thursday night and
Friday. Temperatures rebound on Friday but cloud cover will be the
determining factor reguarding the eventual highs for the day. Models
show lingering moisture at low levels so not looking for a lot of
sun.
A broad upper ridge builds through the end of the week. On Saturday
a weak wave moves will cross the Mid Atlantic area. Will keep chance
of precipitation in the forecast for this time frame.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 130 pm EDT Wednesday...
Late this weekend through mid next week is expected to be dominated
by an upper ridge with the axis on west edge of Appalachians. This
is within a fairly stationary large scale pattern with a deeper
trough remaining over NW U.S., which will help with the extreme fire
situation there, and what is likely to be Tropical Storm Jose well
off the mid-Atlantic and New England coasts. The ridge just to our
west and tropical system in the western Atlantic will keep a light
north or northeasterly flow over the Appalachian region, and models
suggest just enough low level convergence for a very small chance of
isolated showers each day, most likely in afternoon with some
heating and not lasting long. Not a great deal of confidence this
far out in those overall precip chances but it is likely that most
areas on any one of these days will remain dry. Also, should Jose
meander closer to the coast, which only a few out of dozens of model
ensemble members suggest is even possible, this could do two things:
1) create more subsidence over our region to actually reduce any
precip chances, and 2) increase the northerly breezes in the
Piedmont. At this point there is fairly high confidence Jose will
remain far enough offshore to have essentially no impact on our
weather, but of course we will continue to monitor its track.
Otherwise, with this patterns expect seasonable to even slightly
above normal temperatures through this period, with highs in the mid
to upper 70s mountains and lower 80s Piedmont, and lows in the 50s
to lower 60s.
&&
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
As of 727 PM EDT Wednesday...
Initial VFR conditions should begin to deteriorate to a VFR/MVFR
west of I-81 due largely to BKN/OVC stratus mainly after 03z.
Best chance of MVFR at Bluefield and Lewisburg. Intervals of
unrestricted showers will overspread from eastern KY/central WV
as well after 03z to the Blue Ridge and then build into the
Piedmont overnight. Lower-confidence fog forecast as won`t
radiate quite as well though did indicate a temporary MVFR mist
after 09z as moisture levels rise. Winds mainly south under 6
kts becoming light/variable.
Upper low and associated cold pool aloft continues to
overspread the TAFs on Thursday. Expect a continuation of
MVFR/VFR ceilings along with spotty/hit-or-miss light showers.
Really couldn`t discount chance of showers pretty much at any
TAF but any showers unlikely to yield visibility restrictions.
Improvement in ceilings likely to be quite slow on Thursday.
Winds variable initially but should trend light southwest
(at/below 5 kts) late in the day.
Extended Aviation Discussion...
Scattered showers may continue into Friday. Some MVFR showers
are possible on Saturday with another short wave. The chance of
precipitation remains low for Sunday and Monday. Aside from
valley fog in the early morning, conditions overall should be
VFR.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...AMS/WP
NEAR TERM...AL/AMS/WP
SHORT TERM...AMS
LONG TERM...SK
AVIATION...AL/AMS
Area Forecast Discussion
National Weather Service Tucson AZ
957 AM MST Wed Sep 13 2017
.SYNOPSIS...Isolated afternoon and evening thunderstorms will
continue mainly near higher terrain. Becoming breezy to locally
windy on Thursday and Friday with temperatures falling to near
seasonal levels. Moisture then begins to increase on Sunday into
early next week expanding thunderstorm coverage.
&&
.DISCUSSION...A ridge overhead through the desert southwest with
low pressure systems upstream and downstream. This will bring
another day with temperatures well above average across SE AZ.
Still seeing a moisture gradient across the area with about .75
inches in eastern areas and 1.3 inches in the lower deserts (12Z
KTWC sounding in the middle around 1.1 inches). A modest lower
level moisture convergent area is setting up west of Tucson today
with some dry line characteristics. Just enough for the weak
isolated convection showing up on HRRR and UofA WRF forecast runs
to look reasonable. We updated to reflect this a little earlier,
otherwise steady as she goes. Please see the previous discussion
below for details beyond today.
&&
.AVIATION...Valid thru 14/18Z.
VFR with a slight chance of -TSRA/-SHRA near mountains this
afternoon. Normal wind trends mainly less than 12 kts, except in
the upper Gila River valley near KSAD where SFC wind will be NWLY
at 15-20 kts this afternoon. Stronger winds developing Thursday.
Aviation discussion not updated for TAF amendments.
&&
.FIRE WEATHER...We`ll keep enough moisture for a slight chance of
showers and thunderstorms mainly near the mountains. Gusty south
to southwest winds are expected Thursday and Friday as a trough
moves north of the area. Otherwise, 20-foot winds will generally
be terrain driven at less than 15 mph.
&&
.PREV DISCUSSION...Satellite imagery this morning showed an upper
low along CA coast between LA and Frisco while the upper high
that brought record to near record highs yesterday to the area was
centered over northern Sonora. PW values across the area this
morning ranged from 0.75" eastern areas to 1.1" western areas.
Still enough around to support a few mountain storms this
afternoon, especially across the White mountains. Cooler today but
highs will still run 4 to 7 degrees above normal. Could even see
a few spots east of Tucson be close to record highs today.
Localized gusty winds this afternoon, especially in NW-SE
orientated valleys.
Gusty W-SW winds Thursday afternoon as the above mentioned upper low
between LA and Frisco opens up and moves across southern UT &
northern AZ. A few storms possible N-NE of Tucson. Cooler with highs
around normal.
The gusty W-SW winds will be around Friday afternoon as another
upper trof drops into the Great Basin. Forecast high temperatures
will be 2 to 4 degrees cooler than Thursday. A bit of a moisture
increase across far eastern zones for a slight chance of storms.
Models still muddled on how to handle the potential for tropical
moisture to be sent north toward portions of our area later in the
weekend into next week. Confidence continues to be on the low side.
High temperatures for the most part will remain around normal.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
Meyer
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