Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 231748
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1248 PM CDT Wed Jul 23 2014

.UPDATE:
Issued at 1141 AM CDT Wed Jul 23 2014

Several bands of post frontal st/sc as been drifting across the
CWA during the morning...one w-e band from s MO into s IL which
appears to be just behind surface boundary, and a secondary nw-se
oriented cloud deck which formed in the resdiually high moisture
content air north of the cold front that has been working wsw from
southwest and central IL, with the leading edge of this cloudiness
now approaching mid MO/COU area.

Believe with strong July sunshine and drier air advecting into the
region these clouds will gradually break up during the afternoon,
but process could be somewhat slow. Because of this, have backed
off on max temps a couple of degrees most areas.

Other concern for afternoon is thunderstorm threat. Between
1615z-1645z "arc" of echo has appeared over southeast sections of
the CWA from south of Greenville to near Ste. Genevieve, and this
appears to be associated with outflow from morning complex that
worked across far s IL. Don`t think this boundary will get too
much further north due to impact of southward oozing cold front,
but will use this to mark the northern edge of PoPs for this
afternoon. Any surface based storms that do manage to form west
of the Mississippi River will pose some threat of severe weather,
primarily in the form of high winds. This threat should be
confined to our far southern counties where MLCAPES are currently
near 3000 j/kg, with only a limited window of opportunity...roughly
18-20z.

Truett

&&

.SHORT TERM:  (Through Late This Afternoon)
Issued at 330 AM CDT Wed Jul 23 2014

Cold front to continue tracking south through forecast area this
morning, before exiting region early this afternoon. Despite decent
cap over area, could still see some isolated/scattered storms
develop as front moves through. Highest pops will be this morning
for southern half of cwa, then taper off rather quickly after 18z.
As for highs today, will range from the low 80s far north to around
90 far south. Drier/cooler air is lagging behind boundary, so with
dewpts still in the 70s could see heat indicies approaching 95 early
this afternoon.

Byrd

.LONG TERM:  (Tonight through Tuesday)
Issued at 330 AM CDT Wed Jul 23 2014

By tonight, surface ridge begins to build in and bring in drier and
cooler weather for the last half of the work week. Lows tonight will
be in the mid 50s to near 60. Highs on Thursday will be in the upper
70s to low 80s.

Surface ridge to move off to the east by Friday with a warm front
developing across region with elevated convection possible for
northern portions of forecast area late Thursday night through
Friday night. Then as main cold front moves into region on Saturday,
will see additional rounds of storms through Sunday before system
exits region Sunday night. Temperatures to moderate through the
weekend once again. Models are indicating 850 temps between 24C and
26C on Saturday and if they mix down, could see highs in the upper
90s for portions of the area. For now raised highs a few degrees for
Saturday, into the upper 80s to mid 90s.

Beyond the weekend, surface ridge builds in once again for early
next week with highs cooling off into the upper 70s to mid 80s for
Monday and Tuesday.

Byrd

&&

.AVIATION:  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1245 PM CDT Wed Jul 23 2014

Band of post frontal st/sc that formed and/or advected into area
from sw and central IL has given all TAF sites but KCOU a very
definite autumn look throughout the morning. However, over the
last 90 minutes or so visible satellite pics indicate that this cloud
deck (which was roughly centered on a line from just w of KUIN to
near KSTL at 16z) is beginning to break up and ceilings are
beginning to rise. So...believe MVFR cigs in the STL metro should
climb aoa 3kft over the next hour or so...with sct-bkn clouds
3-5kft being the primary sky condition for most of the area during
the afternoon. All of this cloudiness should dissipate heading
into the evening hours with loss of heating and with much drier
air advecting into the region, with clear skies and light
northeast winds expected overnight.

Specifics for KSTL: Bases of MVFR clouds over the area at midday
should climb above 3 kft over the next hour or so...with
additional thinning of the clouds producing sct-bkn deck 3-5kft
throughout the afternoon. The clouds should totally dissipate by
early this evening, leaving clear skies and light northeast winds
for the overnight hours and into Thursday morning.

Truett

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX







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