Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232347
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
547 PM CST Tue Jan 23 2018

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 351 PM CST Tue Jan 23 2018

A broad low pressure system continues to push east northeast out of
the region.  Lingering low level moisture has kept most of the area
under cloudy skies today. A look at recent satellite trends show the
low clouds slowly eroding from the southwest in central and
southeast Missouri. A multitude of model solutions, the RAP/GFS/NAM
indicate various scenarios about the clouds trends overnight. The
most likely scenario will be clouds slowly clearing the area from
southwest to northeast tonight.  An upstream short wave trough will
rotate around the base of the broad trough and will provide a chance
for snow flurries early Wednesday morning over parts of northeast
Missouri and western Illinois. Any clouds associated with the
short wave will exit the region by late Wednesday morning. It will
be warmer tomorrow with highs in the 40s with southwesterly
winds.

Kelly

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 351 PM CST Tue Jan 23 2018

Warmer temperatures can be expected on Thursday as an upper level
ridge moves eastward into the central US, and surface winds become
southerly as a surface ridge shifts well east-southeast of our
region. Highs on Thursday should be around 15 to 20 degrees above
normal. There may be a few sprinkles on Friday as low level moisture
gradually increases over the area with low-mid level warm air
advection.  A better chance of measurable rain begins Friday night
as a deepening upper level trough and associated cold front
approaches.  The ECMWF model and operational GFS models have come
into better agreement than past runs this weekend with rain possible
across most of the forecast area Friday night and Saturday morning,
then the rain should gradually shift southeastward with a chance of
rain continuing across southeast MO and southwest IL, south and east
of STL Saturday afternoon and evening.  The rain should shift
southeast of our forecast area by late Saturday night as a surface
ridge over the northern Plains builds southeastward into our area
behind the cold front.  By the time the colder air advects into our
area Saturday night, the precipitation should shift out of our area
so the precipitation type should be all liquid rain.  Although it
will be colder Saturday night and Sunday the temperatures should
still be slightly above normal.  After more seasonal temperatures
for the end of the weekend into the next work week, a warming trend
will begin Tuesday as southerly surface winds return on the backside
of the retreating surface high, and northwest upper level flow
becomes nearly zonal.

GKS

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 540 PM CST Tue Jan 23 2018

Focus for this TAF period will be the cloud deck covering the
region. Expect this deck to remain in place with little change
tonight. The exception will be that cigs shud drop below 2 kft at
KUIN and KCOU may see clearing late tonight. However, with nwly low
level flow, believe this clearing line will remain just west of
KCOU. If KCOU does become scattered or clear, winds may drop enuf
tonight that fog may develop. Will reassess as new data arrives.

SPECIFICS FOR KSTL/KSUS/KCPS: With MVFR cloud deck in place, do
not expect much change overnight. Cigs shud lift during the
morning hours before finally becoming scattered around 18z.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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