Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 210852
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
352 AM CDT Tue Apr 21 2015

.SHORT TERM: (Through Tuesday night)
Issued at 345 AM CDT Tue Apr 21 2015

Closed H500 low over the UP of MI this mrng will continue to spin
across shtrn Ontario thru mid week keeping the Midwest in NW flow.
Two embedded short waves in the NW flow will affect the region...one
today and the other tonight. The first is expected to pass over the
sthrn CWA this aftn sparking a few showers. Thunder probs look
better today than 24 hrs ago. Precip chances should increase across
sthrn MO from west to east from late mrng thru the aftn...continuing
into the evng. Temps should warm to near avg today with a WSW
wind. Winds will once again pick up later this mrng and become
gusty...esp north of I70 where there will be a heightened fire
danger due to the breezy conditions, RH values below 30% and dry
fuels. Meanwhile...the second short wave is fcst to pass north of
the area tonight pushing a cold front thru the region. There will
be separate precip chance along the bndy as it sinks south
overnight...though the best chances should be across IL...closer
to the better upper lvl support. The front sinks south of the FA
Wed ending any lingering precip threat.

2%

.LONG TERM: (Wednesday through Monday)
Issued at 345 AM CDT Tue Apr 21 2015

A cold Canadian high pressure is fcst to be in control Wed/Thu
producing cool conditions with highs in the mid 50s to low
60s...some 5 to 10 degrees below avg. 850 temps are expected to
approach zero as far south as STL on Wed. Thu mrng appears to be the
coldest mrng with widespread lows in the 30s. Frost will be possible
late Wed night into Thu mrng due to the sfc ridge axis being aligned
over the CWA keeping winds light overnight. The wildcard will be the
potential for a mid cloud deck to edge into the wrn and sthrn
portion of the CWA towards Thu mrng. Seems a bit too early to put
anything in the grids let alone issue a headline but definitely
something to keep an eye on.

Upper heights begin to rise Fri as a weak ridge approaches the area
in advance of the next system. Though the upper lvl features are
similar...the track of the sfc low is substantially different. The
GFS has a much farther south...less thundery...solution than the
ECMWF taking the low from OK into the Deep South while the ECMWF
takes it from KS into the OH Vly. Either way...precip is fcst to
overspread the CWA Fri PM with the best chances Fri night into Sat
mrng. Sat looks like a cloudy cool rainy day...potentially cooler
than the fcst indicates if the GFS solution verifies. High pressure
builds in for Sat night and Sun. NW flow looks like it will redvlp
early next week as another significant trough dvlps. The next chance
for precip arrives early next week as a short wave drops SE.
Significant differences exist at this time so kept PoPs in the
15%-35% range to give guidance to come into better agreement. Temps
are expected to remain aob normal into early next week as NW flow
keeps warmer temps at bay for the foreseeable future.

2%

&&

.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1129 PM CDT Mon Apr 20 2015

VFR through the period. Initially west-southwest winds will become
westerly and increase by mid-morning with 20-30kt wind gusts
expected for most of the day. Winds then decrease quickly after
sunset. A cold front will move through the terminals late in the
TAF period and cause winds to become northwesterly. A few showers
could skirt the I-70 corridor but most precipitation should remain
south of the terminals.

Kanofsky

&&

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

$$

WFO LSX





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