Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 180511

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1111 PM CST Wed Jan 17 2018

Issued at 844 PM CST Wed Jan 17 2018

Forecast on track with few changes made.

A ridge of surface high pressure extended from eastern TX to the
lower OH river valley this evening with a SW flow for much of our
region, with the strongest winds in northern MO and central IL.
Clear skies also prevailed across our region. Temperatures have
dropped into the teens with around 20 in STL.

The ridge of surface high pressure will continue to drop
southward away from our region, allowing SW surface flow to
strengthen some overnight. Despite the clear skies and light snow
pack (less than or equal to 2 inches), the SW winds are expected
to largely stall temps out overnight.

Max temps on Thursday will be substantially higher than
persistence thanks to these SW winds and near maximum sunshine
with continued clear skies.



.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 239 PM CST Wed Jan 17 2018

Surface ridge continues to move eastward through our CWA. Winds
backing to southwesterly overnight into the Thursday morning.
Winds will be 5 to 10 kts with gusts 15 to 20 tomorrow afternoon.
With the ridge in place and southwesterly winds we will see WAA
increase through the night. Overnight temps will reach the mid
teens in most areas. Went slightly above guidance in southern CWA
due to decent warming this afternoon and sightly below guidance in
the northern CWA due to clear skies and snow cover tonight. WAA
should continue to strengthen Thursday and temps will rebound to
near normal highs.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 239 PM CST Wed Jan 17 2018

High pressure will be located over the Gulf Coast on Thursday night
with a tight pressure gradient across Missouri and Illinois.  This
will keep southwesterly surface winds over the area into the
weekend.  850mb temperatures will climb into the 5-10C range over
the weekend, which will allow daytime highs to climb from the 40s on
Friday, to the 50s to near 60 on Saturday and Sunday.  This is
generally supported by the GEFS mean temperatures which show the
warm-up through the weekend as well as lows staying above freezing
on Saturday night.

Dry weather is generally expected through Saturday night and Sunday
before showers develop in the low level moisture convergence ahead of
a upper low that will be moving into the Central Plains.  Will
continue with a likely chance of showers on Sunday night as a cold
front moves through the area.  Will continue with a slight chance of
thunderstorms across southeast Missouri into southern Illinois as
both the GFS/ECMWF are showing some weak instability moving across
the area. In addition, CIPS analogs are also showing some signal for
thunderstorms over the Ozarks on Sunday ahead of the front.
GFS/ECMWF are now showing a dry slot moving in behind the front with
only a limited amount of precipitation with the upper low as it
quickly lifts northeastward.  Will continue to have rain changing to
snow over the northern half of the CWA on Monday afternoon/evening.

Tuesday and next Wednesday looks dry at this point as the global
models show the next surface high moving across the Midwest under
semi-zonal flow.  Highs are expected to be near or just above normal.



.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1111 PM CST Wed Jan 17 2018

VFR conditions and SW surface winds are expected at the TAF sites
thru the valid period. Winds will strengthen somewhat during the
late morning and afternoon hours, with some potential for a brief
gust pushing 20kts possible.

SPECIFICS FOR KSTL: Other than above, surface wind direction
should remain above 210 for the first half of the valid period
with a more definitive slide to below 210 during the mid-late
afternoon and into Thursday evening.





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