Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 302015

Area Forecast Discussion
National Weather Service Saint Louis MO
315 PM CDT SAT APR 30 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 314 PM CDT Sat Apr 30 2016

There remains the potential for a few severe thunderstorms to
develop late this afternoon and early this evening along and south
of a warm front that lies from west northwest to east southeast
across the area.  Clearing over western Missouri has allowed SBCAPEs
to climb into the 1000-2000+ J/kg range.  The RAP still suggests
this instability will move eastward into east central and southeast
MO as well as southern IL by late this afternoon and this evening.
Deep layer shear still support organized severe thunderstorms
capable of producing some severe sized hail and locally damaging
winds.  The experimental HRRR reflectivity suggests that these
storms will move out of the CWA by mid evening.  MOS guidance also
suggest there may be some patchy fog developing after midnight
across the area.


.LONG TERM...  (Sunday through Next Saturday)
Issued at 314 PM CDT Sat Apr 30 2016

(Sunday through Tuesday)

Upper low will move across Iowa on Sunday bringing a weak shortwave
trough across the area.  Will keep chance of showers and isolated
thunderstorms going along and north of I-70 as it passes through.
Sunday night still looks mainly dry before both the GFS/ECMWF brings
another shortwave trough through the area on Monday. Will go with
just a slight chance of showers across much of the area with this
trough.  Northwesterly upper flow will set up over the area by
Tuesday with westerly surface winds, so will keep with a dry

Temperatures will be slightly cooler on Sunday, and then even cooler
on Monday as cold air advects into the area under cloudy skies.
Temperatures should begin to moderate on Tuesday ahead of a cold
front as winds turn out of the west.

(Wednesday through Saturday)

Highly amplified upper flow will continue during the middle and end
of the next week as an omega block sets up over North America.  We
will stay under northwesterly flow aloft during most of this period
with the upper ridge of the omega block approaching from the west by
Saturday.  GFS and ECMWF are in decent agreement that a cold front
will move through the area on Wednesday with just a slight chance of
showers. Temperatures behind the front will be near normal with
850mb temperatures in the 5-10C range until they behind to warm up
by next Saturday.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 108 PM CDT Sat Apr 30 2016

A warm front extending from just north of KCOU to just south of
the St. Louis region into southern IL will gradually advance
northward this afternoon. Flight conditions should improve as this
front moves north of the TAF sites. This front passage may not
occur at KUIN and at that terminal I still tried to be somewhat
optimistic with at least some improvement this afternoon before
IFR conditions settle in again at KUIN overnight and last into
Sunday morning. Scattered thunderstorms should also develop this
afternoon along/ahead of the cold front between 19-21z between
KCOU-KSTL. I have a tempo group in the St. Louis area TAFS to
account for this threat. Shower and thunderstorm threat will
largely remain displaced from the other TAF sites.

Specifics for KSTL:

Flight conditions should improve this afternoon as a warm front
moves north of KSTL. Scattered thunderstorms will also develop
this afternoon along/ahead of the cold front between 19-21z
between KCOU-KSTL. I have a tempo group in the TAF to account for
this threat between 22-01z. Potential for MVFR flight conditions
overnight into Sunday morning due to fog as surface winds become





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