Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241751
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1251 PM CDT WED AUG 24 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 348 AM CDT Wed Aug 24 2016

Main concern continues to be the potential for severe thunderstorms
and heavy rainfall.  Have issued a flash flood watch for tonight for
the potential for heavy rainfall and thunderstorm training.

First area of showers and thunderstorms over northwest Missouri will
continue to move east and will gradually weaken as the low level jet
veers and mid level shortwave races eastward this morning.  Latest
runs of the HRRR also show scattered thunderstorms moving through
areas along and south of I-70 this morning.

Additional thunderstorms will develop this afternoon along and north
of I-70 in advance of of cold front.  MLCAPES will be 2000+ J/kg
with deep layer shear of 35-40kts which will support organized
severe thunderstorms this afternoon and this evening.  In addition,
PWATS will approach 2" with deep warm cloud layers.  The pattern
will also be supportive of cell training, so have issued a flash
flood watch for parts of northeast Missouri into west central
Illinois.

Expect temperatures to climb to near or above normal today with
mixing to near 850mb.

Britt

.LONG TERM...  (Thursday through Tuesday)
Issued at 348 AM CDT Wed Aug 24 2016

The cold front will continue moving slowly south Thursday and
Thursday night.  Current indications are that it won`t be as
unstable Thursday afternoon and evening with MLCAPE mainly in the
1500-2000 J/Kg range.  Additionally, it guidance is showing a decent
amount of CINH along and south of the I-44 corridor in Missouri and
the I-70 corridor in Illinois south of the front.  This should limit
areal coverage and intensity of the storms Thursday afternoon and
Thursday night.  Think greatest chance will continue to be along the
front during the afternoon and early evening.  The focus for
convection will likely shift westward into Kansas during the late
evening where the low level jet will be strongest.  However, 10-15kt
south-southwest flow at 850mb persists over the southern 1/2 of our
CWFA through much of the night, so chance PoPs are warranted.

Looks like good model agreement that the front will drift down over
the Ozarks by 12-15Z Friday morning.  NAM is much faster bringing it
back to the north Friday afternoon, but the GFS and ECMWF keep it
down south of I-70 all day.  Have therefore kept PoPs out of the
northeastern 1/3 of the area.  Warm front moves back to the north by
Saturday morning which will bring warm and humid air back to the
region.  Low level ridge over the Ohio Valley and the central
Appalachians will keep southerly low level flow locked in over our
area through Tuesday.  ECMWF tries to push a weak cold front as far
south as the I-70 corridor Monday night into Tuesday morning, but
the GFS has no front at all...so I didn`t vary temperatures from
Sunday/Monday to Tuesday very much.  There will be a persistent
chance of diurnal convection Saturday through Tuesday in the warm
humid airmass.  Not much to focus convection so blanket
chance/slight chance PoPs are in order.  Temperatures will continue
to be seasonable...primarily in the low to mid 60s for lows and mid
80s for highs.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1240 PM CDT Wed Aug 24 2016

Swly winds will continue and eventually become nwly to nly on
Thurs behind an approaching cdfnt. A number of questions regarding
precip chances thru the period. A line of congested CU has
developed stretching from K1H2, swwd to just south of KCPS to near
KUUV. An outflow bndy, or perhaps a bore wave, is evident in the
latest sat data. Believe this will help initiate TSRA along the
congested CU somewhere east and south of KSTL, but may impact
KCPS, hence the tempo group. Otherwise, best chances for precip
will be at UIN this evening into the overnight hours. This area of
precip shud lift NE of the region Thurs morning.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Knox MO-Lewis MO-Marion MO-Monroe MO-Ralls MO-
     Shelby MO.

IL...Flash Flood Watch from 7 PM CDT this evening through Thursday
     morning for Adams IL.

&&

$$

WFO LSX


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