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FXUS63 KLSX 202335

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
635 PM CDT Tue Mar 20 2018

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 346 PM CDT Tue Mar 20 2018

Surface high pressure over the Great Plains will build slowly east 
through Wednesday.  Water vapor imagery is showing a shortwave over 
South Dakota and Nebraska that will drop southeast through the 
Missouri Valley across western Missouri tonight. Short range 
guidance is developing some light precip over west central and 
central Missouri this evening as the wave ripples by.  Low levels 
look relatively dry so I'm not sure how much precip will actually 
reach the ground.  Regardless, thermal profiles suggest that the 
most likely precip type will be liquid if anything does reach the 
ground.  Clouds overnight will likely keep temperatures from 
bottoming out too hard, but lows in the upper 20s to low 30s look 
likely.  Should see a clearing sky on Wednesday as high pressure 
continues building into the Mississippi Valley from the west.  March 
sunshine is expected to help temperatures rebound into the upper 40s 
and low 50s.


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 346 PM CDT Tue Mar 20 2018

Low level flow turns back to the southwest on Thursday as the 
surface high moves east of the Mississippi Valley.  Models have been 
consistently printing out precip Thursday and Thursday night as the 
nose of a 20-30kt low level jet pushes into the 850mb baroclinic 
zone resulting in weak to moderate moisture convergence and 
isentropic lift.  There's still some question though about how much 
moisture will be available to generate precip as the retreating 
ridge axis extends all the way south into the central Gulf of 
Mexico.  Have therefore limited PoPs to the chance range rather than 
going higher in spite of the model consistency and good agreement.

Medium range guidance is trying to come into better agreement for 
Friday through Sunday with the next storm system.  The low is 
forecast to develop over eastern Colorado and western Kansas late 
Friday and move into Missouri Saturday.  The low moves east-
southeast into the Tennessee Valley by Saturday night and the 
southern edge of a large Canadian high pushes in from the northeast 
behind the low.  This looks like another good chance for rain across 
much of Missouri and Illinois...with strong moisture convergence 
wrapping around the cold sector of the low.  Sunday looks dry at 
this time between a strong upper level ridge moving overhead and the 
surface high pushing cool dry air in from the east and northeast. 
The longwave pattern continues to progress east with a deep trof 
developing over the Western U.S. and the upper ridge moving over the 
Eastern Seaboard on Monday. Resulting southwest flow over the 
Central U.S. will provide deep moisture return into the Mississippi 
Valley and an increasing chance for rain early next week.



.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 614 PM CDT Tue Mar 20 2018

Nwly to nly flow expected thru the TAF period. Believe cigs will
remain VFR, however, some MVFR cigs may develop further west and
impact COU. There is also a chance of rain, or perhaps light snow,
impacting COU tonight. 

SPECIFICS FOR KSTL: VFR conditions thru the period expected. Winds
will remain nwly to nly and increase Wed morning, then diminish
again after sunset. 



Saint Louis     33  49  33  54 /   5   0   0  40 
Quincy          29  47  30  50 /  10   0   0  50 
Columbia        32  51  33  61 /  10   0   0  10 
Jefferson City  32  52  31  62 /  10   0   0   5 
Salem           32  47  29  52 /  10   0   0  30 
Farmington      31  50  30  58 /  10   0   0  10 



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