Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/16/17
Area Forecast Discussion
National Weather Service La Crosse WI
635 PM CDT Fri Sep 15 2017
.SYNOPSIS...
Issued at 130 PM CDT Fri Sep 15 2017
GOES water vapor imagery this afternoon showing an impressive mid-
level cyclonic circulation lifting from WY toward the Dakotas. This
was producing surface cyclogenesis over the Central Plains with
increasing moisture transport ahead of this low into our area. RAP
analysis has axis of 850mb moisture transport extending from eastern
KS northward into western MN. Have been watching an area of showers
and isolated thunderstorms lifting slowly northeast toward our
forecast area in northeast IA/southeast MN on the eastern
periphery of this moisture transport. Believe the bulk of this
activity will stay just west of the area through the remainder of
this afternoon/early evening. Otherwise, temperatures as of 2pm
this afternoon were in the 80s.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 130 PM CDT Fri Sep 15 2017
Going into tonight...low pressure will lift northeast across western
MN, drawing the surface cold front a bit further east into central
MN through northwest IA. Main axis of moisture transport/fuel for
convection looks to remain just west of our area but will likley see
isolated to scattered showers/storms nudge into western portions of
the forecast area (mainly northwest of a line from Charles City Ia
to Medford WI). This area will be on the very eastern fringes of
this better moisture transport. Otherwise, look for a rather muggy
overnight with lows in the middle/upper 60s with dew points in the
lower 60s.
The cold front oozes ever so slowly eastward toward the area on
Saturday, extending from northwest WI through south central MN by
late in the afternoon. This keeps bulk of showers/storms west of the
area through the day with continued warm air advection across our
area. 925mb temperatures in the 23-25C range in the afternoon, so
should see unseasonably warm highs again in the 80s, coolest over
the northwest where more cloud cover is expected.
.LONG TERM...(Saturday night through Friday)
Issued at 130 PM CDT Fri Sep 15 2017
Vigorous mid-level trough rotating northeast into the easter
Dakotas.northwest MN drives the surface cold front across our area
Saturday evening/overnight. CAPE will be waning going into the
nighttime hours and Bulk Shear is mostly post-frontal, so severe
threat looks minimal at this time. However, cannot rule out a few
stronger storms with small hail and gusty winds.
After some lingering morning shower chances, drier/cooler air will
filter into the area Sunday. Look for mostly sunny skies by
afternoon with highs in the upper 60 to the middle 70s, which is
right around seasonal normals.
High pressure shifting off to the east already by Sunday night as
a mid-level trough ejects out of the Central Plains toward our
area. This will produce a chance of showers west of the
Mississippi River after midnight.
For next week...southwest flow aloft will keep the area in
occasional shower/thunderstorm chances as several mid-level
disturbances eject out of the main trough out west into our area.
Otherwise, temperatures are expected to be slightly above normal
through this period with highs in the middle/upper 70s and lows in
the middle 50s/lower 60s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 635 PM CDT Fri Sep 15 2017
Quiet weather conditions are set to continue into the evening
hours for all areas, with just some passing cirrus as low level
wind shear becomes the biggest issue from about 03Z onward for all
areas. Another push of moisture into the area (similar to last
night) should result in developing mid level clouds and likely at
least scattered showers and thunderstorms late tonight,
particularly near and west of the RST terminal. Given uncertainty
in coverage/placement, will stick with a vicinity mention at this
point and continue to watch trends. There is a very low end chance
that a shower or storm gets closer to LSE as well through mid
morning, though that risk is quite low per current forecast
trends. Otherwise, surface winds should again become gusty into
the midday and afternoon hours on Saturday, with any lingering
morning showers/storms ending and ceilings dissipating.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SYNOPSIS...DAS
SHORT TERM...DAS
LONG TERM...DAS
AVIATION...Lawrence
Area Forecast Discussion
National Weather Service Cheyenne WY
551 PM MDT Fri Sep 15 2017
.SHORT TERM...(This evening through Sunday night)
Issued at 245 PM MDT Fri Sep 15 2017
Just a few showers noted so far this afternoon over parts of the
CWA as the area is likely seeing some subsidence behind a
departing shortwave ejecting north over the northern high plains.
Another wave over Utah should bring another round of mainly
showers to the CWA this evening, with some snow possible over the
highest peaks. Little accumulation expected however. Pcpn should
end Saturday morning with the passage of the main upper trough. A
cold front will move across the CWA this evening with mins falling
into the 40s over much of the CWA, with some 30s over western
valleys.
Saturday will feature mild temperatures across the CWA with some
fairly breezy winds out west in the afternoon as decent westerly
mid level flow mixes down. The winds will drop off in the evening
with clearing skies setting up a chilly night Saturday night. Mins
could get close to or even a bit below freezing in low lying areas
such as Alliance and western valley locations Sunday morning.
Return flow during the day Sunday will allow warmer temperatures
over the plains as upper flow backs to southwesterly.
.LONG TERM...(Monday through Friday)
Issued at 245 PM MDT Fri Sep 15 2017
Looking at a rather active week weather-wise, especially from
Tuesday onward. Southwest flow aloft will provide dry and warm
conditions to start the work week. A vigorous upper level jet will
carve out a fairly deep trough from the northern Rockies to the
southern Great Basin Tuesday. A Pacific cold front will surge
southeast across the CWA Tuesday night, accompanied by scattered
showers. Instability for thunder will be marginal at best. High
temperatures Wednesday will be 10 degrees cooler compared to
Tuesday. The upper trough lifts northeast into the northern Great
Plains and upper Midwest later Wednesday, with the next upper jet
maxima and trough tracking east then northeast across the CWA
Wednesday night and Thursday with scattered showers. Highest
elevations west of the Laramie Range may see some snow, but no
significant accumulations are expected. The third in a series of
upper troughs will be deeper as it tracks across the Intermountain
West Friday. Shortwave energy in deepening south-southwest flow will
trigger more shower activity at that time. High temperatures by the
end of next week will trend near to below seasonal normals. Most
days will be breezy, mainly along and west of the Laramie Range.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 550 PM MDT Fri Sep 15 2017
More widespread IFR conditions expected tonight across the
Nebraska Panhandle and east of the Laramie Range. Should start
earlier too with recent rainfall and upsloping winds already
ongoing. Generally followed HRRR guidance on timing/locations of
IFR onset.
&&
.FIRE WEATHER...
Issued at 245 PM MDT Fri Sep 15 2017
A cold front will move across the districts this evening with
showers and possibly a thunderstorm or two behind the front.
Wetting rains look to be rather isolated though. A little snow is
even possible over the highest mountain peaks overnight. Mild and
mainly dry weather is then expected Saturday and Sunday with some
breezy afternoon winds over western areas.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...RE
LONG TERM...MAJ
AVIATION...GCC
FIRE WEATHER...RE
Area Forecast Discussion
National Weather Service Des Moines IA
649 PM CDT Fri Sep 15 2017
...Updated Aviation Discussion...
.SHORT TERM.../Tonight through Saturday/
Issued at 338 PM CDT Fri Sep 15 2017
Tonight...A low and associated deep upper trough will begin to pivot
northeast. This will drive a shortwave across the region tonight
and push an elongated surface low and associated cold front into
northeast MN and southeast NE. Ahead of this boundary will be a wave
of theta-e advection and some weak to moderate lift. This should be
sufficient to have showers and storms. However, instability is only
modest and shear is negligible so the better storms will remain west
of the forecast area tonight with showers/isolated storms expected
to dribble across the area. The HRRR handled things today the best
and leaned towards that model for tonight though all models point to
only weak showers/convection tonight. The NAM is the most bullish
and mainly across the west. I`ve gone with that main thinking but
tempered pops/qpf to be more in line with the HRRR.
Saturday...The aforementioned cold front will slowly make it`s way
across the state Saturday into Sunday. By 00Z Sunday the front
should only be through about the Western third of the state. The
best forcing and shear lag the front somewhat and there is some
uncertainty as to what the morning showers and cloud cover will do
to the instability so overall, not expecting much during the day but
may see showers with isolated storms. By afternoon...especially
late afternoon into Saturday night, we should see enough sun and
destabilize enough that storms should develop along/behind the
frontal boundary, some of which could be strong to severe. Shear is
mostly unidirectional so large hail with maybe some damaging wind
would be the threat going into the evening. Strongest storms should
hold off til the evening but west of highway 169 would be of concern
late in the day.
.LONG TERM.../Saturday night through Friday/
Issued at 338 PM CDT Fri Sep 15 2017
Increased kinematic forcing into Saturday evening should help any
afternoon convection to increase along the boundary across western
into central Iowa. Sufficient shear exists for some organization
and a convective line is likely to develop by early evening.
Some severe weather will occur in the evening with main threats
from damaging winds and large hail. The convection will spread
quickly southeast overnight as surface front moves through the
state with relatively dry and cooler conditions for much of
Sunday. However, upper flow will persist from the southwest and a
return to warm advection is expected by Sunday night along with
increasing low level moisture transport. Elevated convection is
expected to spread northward into the state overnight into Monday
morning with best threat in central and southern areas.
Thereafter, warm sector will spread northward into the state as
large western trof develops. As this trof deepens and matures, a
surface boundary is expected to move into the state toward the
middle of next week. Both Euro and GFS indicate a period of active
weather with periods of thunderstorms and the possibility of heavy
rainfall. Temperatures will remain generally at or above normal
with southerly flow into the state for much of the week.
&&
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 643 PM CDT Fri Sep 15 2017
Expecting VFR conditions throughout the TAF period. The main
concern is with storm potential over northern Iowa and possibly
impacting MCW and FOD. Certainly VCTS seems viable for MCW and FOD
towards Saturday morning, but low confidence in mentioning any
MVFR visibility due to the coverage and duration of the
convection. Winds continue to mix through the evening hours
tonight before subsiding somewhat overnight. However, they
increase again late Saturday morning into the afternoon as a deep
trough advances towards the state.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...FAB
LONG TERM...Cogil
AVIATION...Podrazik
Area Forecast Discussion
National Weather Service Quad Cities IA IL
553 PM CDT Fri Sep 15 2017
...00Z AVIATION UPDATE...
.SYNOPSIS...
Issued at 250 PM CDT Fri Sep 15 2017
18z surface data has low pressure over central Nebraska and high
pressure over the Ohio Valley. A front ran northeast from the low
into eastern Lake Superior. Dew points were mainly in the 60s across
the Midwest with some 50s across eastern Iowa.
&&
.SHORT TERM...(This Evening through Saturday)
ISSUED AT 250 PM CDT Fri Sep 15 2017
Very warm and dry conditions will be seen through sunset. After
sunset the dry conditions will continue through midnight. Attention
then turns to the late night time frame.
After midnight, the RAP model has a layer of unstable air aloft,
that, when combined with some weak forcing and moisture generates
some elevated convection. This situation occurred last night and
resulted in showers and a few thunderstorms.
So, based on this persistent signal from the RAP, slight chance to
low chance pops have been introduced for areas west of a Manchester,
IA to Williamsburg, IA line. The rain from the elevated convection
will fall through a dry layer that is around 10 kft deep. So, while
the nocturnal convection may look impressive on radar, the amount of
rain at the surface may just barely wet the pavement.
The nocturnal convection that develops late tonight will dissipate
around mid morning Saturday. Once the clouds break up, very warm
conditions will be seen across the area with high temperatures
ranging from the mid 80s to the lower 90s. Dew points will drop
during the day but heat index readings are still expected to be in
the upper 80s to lower 90s.
Refer to the climate section for record highs for September 16th.
.LONG TERM...(Saturday Night through Friday)
ISSUED AT 250 PM CDT Fri Sep 15 2017
Long term forecast highlights are unseasonably warm temps through
next week, along with potential for some relief from the recent dry
spell.
A well-advertised cold front will finally arrive Saturday night into
Sunday. Highest rain coverage is favored along/west of the
Mississippi River. Areal averages should be less than 1/4 inch, with
isolated pockets of heavier rain with isolated storms. This will not
provide much relief for the drought conditions across southeast
Iowa. Weak deep layer shear and forcing should preclude any
organized severe weather threat. Clouds and a south breeze will keep
lows Saturday night well above normal, mainly in the 60s.
Sunday, expect scattered showers and a few storms to linger as the
front pushes south of the area. A cooler and drier air mass will
overspread the area, with afternoon highs in the mid 70s to around
80.
Early next week, there is more favorable model consensus regarding
the arrival of another short wave trough embedded in southwest flow,
along with a warm front across the forecast area. This scenario
could yield some more widespread significant rain Monday and/or
Monday night, although confidence in details remains low.
Looking ahead, expect highs warming into the 80s Tuesday/Wednesday.
The ECMWF and GFS are both advertising more rain for Wednesday.
Temps will remain above normal through Friday, with additional late
week chances of showers and thunderstorms. Model blend pops indicate
at least some potential for rain every period. This is overdone, but
no period can be reliably ruled out at this point.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 544 PM CDT Fri Sep 15 2017
VFR conditions expected to persist through the TAF cycle. Several
convective allowing models continue to suggest the potential
for elevated SHRA and possibly an isolated TSRA moving into
eastern IA late tonight until mid morning Saturday while weakening.
KCID still appears to have best potential of being impacted by
a SHRA or TSRA that may result in brief period of MVFR conditions
(visibility), but given anticipated weakening trend have maintained
VCSH wording at KCID and also at KDBQ toward 12z through 16z.
Otherwise, expect periods of mid and high clouds with winds backing
to SE at 4-8 kts tonight then veering to SSW on Saturday at 10-20 kts.
&&
.CLIMATE...
ISSUED AT 250 PM CDT Fri Sep 15 2017
Record Highs for September 16...
Moline.........92 in 1931
Cedar Rapids...98 in 1931
Dubuque........96 in 1931
Burlington.....95 in 1906
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
SYNOPSIS...08
SHORT TERM...08
LONG TERM...RP Kinney
AVIATION...McClure
CLIMATE...08
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1014 PM CDT Fri Sep 15 2017
.UPDATE...
Quick update to add some slight chance PoPs to far northwestern Val
Verde County due to shower activity on the KDFX radar. Based on the
HRRR this activity should stay confined to areas just north and west
of our area, but a brief shower could work into Val Verde County over
the next one to two hours. Otherwise, the rest of the forecast is on
track with increasing clouds overnight and patchy fog by morning.
&&
.PREV DISCUSSION... /ISSUED 649 PM CDT Fri Sep 15 2017/
AVIATION.../00Z TAFS/
Will maintain a near persistence forecast with I-35 sites seeing low
cloudiness return around midnight and some spotty ifr cigs by around
10Z. Afternoon and early evening pressure gradients look to tighten
up from mixing of stronger winds aloft with decoupling late at night
expected to yield the ifr conditions. The gradient holds tighter
over DRT so will keep their cigs as mvfr and short-lived in the late
morning hours. A few showers are suggested to be in the picture near
DRT by rapid refresh models. Will wait for the 06z update to consider
introducing any impacts as they should be minor.
PREV DISCUSSION... /ISSUED 248 PM CDT Fri Sep 15 2017/
SHORT TERM (Tonight through Saturday Night)...
Upper air analysis this morning showed a shallow trough over the Gulf
of Mexico with a low amplitude ridge over West Texas. The flow over
South Texas was northwesterly. At the surface, high pressure was
centered to our east and winds were from the south to southeast.
There was a trough over West Texas producing convection. This
activity will stay north of our CWA as it dissipates this evening.
The upper level ridge will become dominant during this period. The
low level flow will remain south to southeasterly, so we don`t
expect much change in the weather. Continuing flow from the Gulf will
bring high temperatures down a couple of degrees Saturday. Patchy
will form again overnight along and southeast of I-35. A spots could
have visibility as low as a half mile.
LONG TERM (Sunday through Friday)...
The upper level ridge will move to the southwest into the middle of
next week. In response, upper flow will become more zonal by Tuesday.
During this transition, a short wave trough will move across Central
Texas and bring a chance for showers and thunderstorms Monday and
Tuesday across the eastern half of the CWA. Tuesday night into
Wednesday an upper trough will dig down across New Mexico and pick up
the remnants of Tropical Storm Norma from the Pacific. This will
bring another chance for rain Wednesday and Thursday across all of
South Central Texas.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 92 72 92 71 91 / 0 0 - 0 10
Austin Bergstrom Intl Airport 92 71 91 69 91 / 0 0 - 0 10
New Braunfels Muni Airport 92 71 93 70 91 / 0 - - 0 10
Burnet Muni Airport 92 70 91 69 90 / 0 0 0 0 -
Del Rio Intl Airport 100 73 96 73 95 / 0 0 0 0 -
Georgetown Muni Airport 90 71 91 69 90 / 0 0 0 0 10
Hondo Muni Airport 98 70 96 70 94 / 0 0 0 0 10
San Marcos Muni Airport 92 71 92 69 90 / 0 0 10 0 10
La Grange - Fayette Regional 93 71 91 70 91 / 0 0 10 - 20
San Antonio Intl Airport 92 72 93 71 91 / 0 - 0 0 10
Stinson Muni Airport 95 72 93 72 92 / 0 0 0 0 10
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Mesoscale/Aviation...Oaks
Synoptic/Grids...Treadway
Public Service/Data Collection...30
Area Forecast Discussion
National Weather Service North Platte NE
713 PM CDT Fri Sep 15 2017
.SYNOPSIS...
Issued at 311 PM CDT Fri Sep 15 2017
Well defined lead PV anomaly moving northeast across eastern WY on
downstream side of long wave trough located over the western US.
Ahead of this feature strong LLJ and low level warm air advection
creating a large area of mid level instability across eastern NE
into SD/MN. Within this environment SHRA and TSRA developed as a
result of forcing of a northward advancing warm front last night and
through the morning. Further west, more widespread rain and even
snow in the higher elevations across parts of MT/WY supported by
fairly substantial cold conveyor belt across southern Canada
combined with warm conveyor belt originating from the aforementioned
LLJ and warm advection pattern through the Dakotas and turning
westward and wrapping into the low. Second and more substantial
PV anomaly dropping southward on backside of upper low over
eastern WA/OR into NV/UT.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 311 PM CDT Fri Sep 15 2017
Previously mentioned PV anomaly will rotate through the upper low
across the central Rockies today. Downslope winds will drive/create
a dryline surge across northeast CO and western KS and into
southwest/central NE this afternoon. Surface low will continue to
pull northeast into western MN and weaken as it stays anchored to
broader area of weakening warm air advection. Associated subsidence
behind exiting short wave to be in place across western NE into the
afternoon. Slight precip chances near the SD border late this
afternoon but large scale subsidence should keep most of the area
dry through late afternoon.
As PV anomaly moves off the Rockies it will cause a surface low to
develop in northeastern CO and allow a cold front to drop south into
the Panhandle this evening. Upper height falls then rotate into the
western Dakotas late afternoon and evening and low level winds
respond resulting in convergence along the front across northeastern
NE and to some degree along the dryline in central NE by evening.
RAP soundings suggest inverted-V profiles in low levels west of this
line, suggesting dry air below a shallow moist layer in the mid
levels. This profile exists to some degree in eastern north central
NE in the form of an elevated mixed layer and therefore allows some
CAPE/instability to be available above low level forcing and should
set the stage for thunderstorm development if parcels can make it
above low level stable layer. Short range models differ on this
occurring, but if it does there will be decent potential for enough
instability to produce updrafts capable of supporting marginal large
hail, hence the area of marginal risk for severe storms as presented
by SPC.
Further west, weaker elevated instability moves into the NE
Panhandle this evening. Next area of height falls associated with
next PV anomaly rotating through main upper trough will allow mid
level southerly winds to increase across the west creating a new
warm conveyor belt and developing an area of strong frontogenetic
forcing in this weakly unstable environment in the Panhandle. More
widespread showers and a few thunderstorms will develop as a result
of the strong mid level forcing, moving east across north central NE
overnight. Though some instability is presented in RAP soundings in
this area it likely won`t be enough to support large hail. Good
confidence in the occurrence of SHRA/TSRA here however as this
sequence of events is supported by most models.
For saturday some lingering showers and maybe a rumble of thunder or
two will be across north central NE. But otherwise expect a lot of
cloud cover behind the front and much cooler temps. Upper low pulls
northeast into the Dakotas and although some weak forcing with
remain across north central NE this will lessen through the day.
.LONG TERM...(Saturday night through Friday)
Issued at 311 PM CDT Fri Sep 15 2017
An active weather pattern will be taking shape the next several days
as a large upper trough becomes established across the Pacific
northwest. This trough will slowly move east into the central and
northern plains by the end of next week.
Ahead of this large trough, a weak disturbance will quickly move
east across the area Sunday into Sunday night. Will include some
chance pops for precipitation with this. Appears enough instability
to include thunder.
As the upper trough slowly moves east next week, isolated to
scattered showers and thunderstorms will be possible by midweek as
southwest flow aloft becomes established on the eastern periphery
of the approaching trough. Will keep pops conservative as quite a
bit of model differences at this point.
After a cool weekend, it will begin to warm up again ahead of the
upper trough early next week. It appears highs in the upper 70s and
80s will return through much of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 711 PM CDT Fri Sep 15 2017
Clouds will increase with MVFR CIGS likely by late evening.
Ceilings will range from 1000 to 1500 FT AGL. Look for skies to
gradually clear Saturday afternoon. Light showers will be possible
at the KVTN terminal tonight. Will handle this with a vcsh group
given the expected sparse coverage of showers.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Stoppkotte
SHORT TERM...Stoppkotte
LONG TERM...Taylor
AVIATION...Buttler
Area Forecast Discussion
National Weather Service Marquette MI
816 PM EDT Fri Sep 15 2017
.SHORT TERM...(This evening through Saturday)
Issued at 403 PM EDT FRI SEP 15 2017
Another day with the stalled front and trough across the area. Main
impacts are thunderstorms, with an outside chance of a stronger
storm, far west over the next 2-3 hours, moderate swim risk through
this evening for Schoolcraft County, high swim risk for Schoolcraft
County Sat, dense fog potential across the Keweenaw tonight, and
possibly some strong to severe storms over the W on Sat.
.
Thunderstorms have formed over NW WI, far W U.P. and far W Lake
Superior as a weak shortwave lifts through. CAPE values up to 1,000
J/kg over the west with weak shear may result in a stronger storm or
two, but think chances of that are small. HRRR and RAP are also
showing some precip breaking out over the NCentral as the shortwave
passes, which is possible given the lake breeze there as an
additional focusing mechanism. Have slight chance PoPs over the
NCentral.
Ahead of an upper wave and the SFC low riding up the front, precip
may skirt the western U.P. Sat, with greater chances for precip as
the wave/low approaches later in the day. Some of the storms could
be strong to severe given potential for up to 2,000 J/kg of cape and
effective shear values of 20-30kts. Large hail and damaging winds
the primary threat.
Dense fog is possibly over the Keweenaw tonight with E winds off the
Lake. Not confident enough to issue any headlines though.
With large waves along the beaches of Schoolcraft County, the mod
swim risk will continue into this evening, with larger waves and a
high swim risk on Sat. The night shift will issue the headline if
needed.
.LONG TERM...(Saturday night through Friday)
Issued at 348 PM EDT FRI SEP 15 2017
Guidance continues to hold onto the dominant upper level ridge
across the eastern CONUS through the weekend; however, there
continues to be some nudging to the east which could bring the
upstream trough further east towards the Upper Peninsula. Will
continue to bring steady increases of precip and possibly thunder.
With a low pressure system lifting north of the forecast area Sun,
guidance indicates a frontal boundary will precede a surface ridge
of high pressure late in the weekend into early next week. This will
then allow dry weather to return.
The pattern does start to become more active with a quasi-zonal
orientation from Tue-Thur of next week. This will bring periodic
chances for showers and possibly thunder, but also with more
seasonal temps.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 806 PM EDT FRI SEP 15 2017
LLWS at all sites tonight. Expect showers to generally hold off to
the west through much of the period.
At KCMX, LIFR to VLIFR conditions in CIGS and fog are expected
into early overnight with eastern flow off the lake and plenty of
upstream low level moisture. Conditions should improve late
tonight to VFR as winds shift to a downslope southeast direction.
At KSAW, moist southeast upslope flow could lead to some patchy
fog/stratus late tonight but uncertainty is such that kept VFR
conditions thru the period.
At KIWD, moist northeast flow off Lake Superior will lead to LIFR
stratus clouds early this evening but once winds shift southeast
later this evening expect improvement to VFR.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 403 PM EDT FRI SEP 15 2017
An inverted surface trough currently anchored across Lake Superior
will begin to weaken tonight. NE winds to 20 to 30 knots may
occasionally gust to 35 knots into early tonight before weakening.
Winds will then increase on Sunday out of the W gusting to 20-30
knots. Otherwise, winds will be below 25 knots..
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Titus
LONG TERM...Beachler
AVIATION...Voss
MARINE...Titus
Area Forecast Discussion
National Weather Service Topeka KS
610 PM CDT Fri Sep 15 2017
...AVIATION UPDATE...
.SHORT TERM...(This evening through Saturday)
Issued at 336 PM CDT Fri Sep 15 2017
The early afternoon water vapor satellite imagery featured a deep
longwave trough positioned over the inter-mountain west with multiple
subtle perturbations rotating around its base and ejecting to the
northeast. One such wave helped prolong an area of showers and
isolated thunderstorms across central Kansas. Despite a 10 kft deep
wedge of dry air below cloud base, precip managed to reach the
ground thanks to the added kinematic lift associated with the
departing shortwave. At the surface, an elongated 1002 mb surface
low was located near the the Siouxland region with a trailing cold
front stretching southwestward and into far NW Kansas. NE Kansas was
located in the warm sector ahead of this front, but clouds from the
daytime precip resulted in a complex thermal field in the early
afternoon analysis.
Over the next 24 hours, the upper level longwave will pivot ENE into
the western Dakotas as a 90 kt jet streak wraps around the base of
the trough. This will help push the cold front southeastward during
the day tomorrow, approaching Concordia by the mid to late
afternoon. Aside from a slight chance of showers and storms with the
nocturnal LLJ early tomorrow morning, the next best chance for
storms will be along and ahead boundary tomorrow afternoon. MLCAPE
values will likely exceed 3000 J/kg due to steepening mid-level
lapse rates and ample surface heating ahead of the boundary.
However, the best jet dynamics and deep shear look to stay north of
the CWA. Thus, the best threat for stronger storms will be in the
incipient stages of any convection, with large hail and localized
damaging winds the main threats. This is in agreement with the SPC
Day 2 marginal outlook.
.LONG TERM...(Saturday night through Friday)
Issued at 336 PM CDT Fri Sep 15 2017
Front continues southeast through the area Saturday night, through
not terribly fast with upper flow nearly parallel to it. Should
still be enough forcing and moisture for decent coverage despite
some capping remaining with a few near-severe storms possible until
ML CAPE diminishes in the late evening. Not seeing any obvious signs
of a persistent training situation but some locations could see
locally heavy amounts. Expect decreasing coverage with time late in
the night into midday Sunday with chances increasing again Sunday
night into Monday as isentropic upglide develops through the column
and the southern branch jet comes into Oklahoma for added ascent in
its left-front quadrant. Not much focus in the ascent noted at this
time though still high-chance to likely PoPs are warranted and
elevated CAPE increasing to around 1000 J/kg could produce some
small hail. Will need to watch how much the warm sector moderates
Monday afternoon with the potential for a decent shear/ML CAPE
combination and suggestions of low level convergence remaining. Low-
level jet increase Monday night for another chance for elevated
storms. Western CONUS upper trough deepens into the midweek as
multiple waves rotate through it. Current operational models are
fairly consistent with another Pacific cold front passing through
Tuesday night and Wednesday though, though southwest flow in the mid
levels could bring a decent cap in. Have kept chances limited at
this point. Somewhat better precip chances come late in the
forecast with the upper trough pushing a bit farther east. As for
temperatures, Sunday still looks the coolest of the week with
highs perhaps not breaking the mid 70s in some locations. Highs
return to the 80s for the remainder of the week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday)
Issued at 610 PM CDT Fri Sep 15 2017
Mid level warm air advection continues over the area, although
I`m not sure how much moisture advection is occurring with mid
level moisture already in place. Forecast soundings hint at some
brief saturation overnight implying some elevated storms could
develop. But with the RAP and HRRR showing isolated precip at
best, think including a VCTS may be a little to aggressive at this
point. As for LLWS, forecast soundings maintain good mixing of
the boundary layer through the night with a very shallow inversion
at best. LLWS remains a concern with a 40KT+ low level jet and
will keep a mention of it for TOP where there is a better chance
for surface winds to back more to the southeast. However at MHK
and FOE think there is a better chance for surface winds to remain
gusty through a good portion of the night as models maintain a
good surface pressure gradient over the area. In general VFR
conditions should prevail into Saturday with a FROPA and chances
for TS anticipated just beyond the forecast period.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Skow
LONG TERM...65
AVIATION...Wolters