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FXUS63 KLSX 151000

Area Forecast Discussion
National Weather Service Saint Louis MO
400 AM CST Fri Nov 15 2019

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 325 AM CST Fri Nov 15 2019

The flow aloft will be in transition over the next few days as the
upper trof across the lower MS Valley departs slowly eastward and
a northern stream upper trof swings from the Hudson Bay vicinity
eastward. This flow regime will maintain high pressure across the
region through the period to varying degrees. The surface high 
currently centered through the area will gradually retreat 
eastward however a prominent southwestward extension of the high 
will persist through Saturday. The result will be a continuation 
of below normal temperatures with only very slight day to day 


.LONG TERM...  (Saturday Night through Thursday)
Issued at 325 AM CST Fri Nov 15 2019

The latest NWP guidance is all pointing at increasing rain chances
Sunday into Sunday evening, much higher than the previously
forecast. A deepening upper trof will move into the Plains on
Saturday and into the Mississippi Valley on Sunday, exiting into
the western TN/OH Valley overnight Sunday. This is a rather
impressive upper trof and while there are some variations on the
depth and exact positioning, large scale ascent with the trof
along with mid level frontogenetic forcing should result in a band
of rain developing and spreading from west to east across the CWA
along/ahead of the associated advancing cold front. Present 
thinking is this should all be rain with low level warming
indicated with the GFS and ECMWF. This initial upper trof will
contribute to the development of a long wave trof centered through
the eastern U.S. on Monday and northwest flow across the region. 
A short wave within this northwest flow will then traverse the 
region Monday afternoon/night with an attendant cold front. 
Currently this system looks dry with a lack of an organized signal
for precipitation.

A pattern change ensues Tuesday into the later part of next week
with an amplified split flow pattern taking shape anchored by an
upper low/trof in the western U.S.. Rising heights associated with
ridging aloft and the return of southerly low level flow will
bring a warm-up and above normal temperatures to our area
Tuesday-Wednesday. Deterministic models and ensembles show a 
chance of precipitation in the Wednesday night-Thursday time frame
as a lead short wave trof and attendant cold front move through 
the MS Valley. 



.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1110 PM CST Thu Nov 14 2019

VFR conditions, light surface winds, and dry weather are expected
to prevail at the TAF sites through much of the valid period. The
main exception will be fog early Friday morning, where despite 
opposition of nearly all guidance, conceptual models support some 
fog potential due to recent snowmelt across the region and ideal
radiational cooling conditions.  




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