Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 201740
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1240 PM CDT Mon Apr 20 2015

.UPDATE:
Issued at 1240 PM CDT Mon Apr 20 2015

With a lot more sc than originally forecast and breezy northwest
winds, temperatures are not warming up as much as previously
thought. So increased cloud cover and lowered highs between 2 to 5
degrees most locations. Also, secondary shortwave sliding
southeast through region on backside of system generating some
isolated showers/sprinkles for northeastern/east central MO and
west central/southwestern IL this afternoon.

Byrd
&&

.SHORT TERM: (Through Wednesday)
Issued at 329 AM CDT Mon Apr 20 2015

A significant upper lvl trof has dvlpd across the cntrl CONUS over
the wknd and should affect the CWA thru at least the first half of
the week mvng from near KINL to north of Lake Huron by Wed. The week
will feature slightly below normal temps with highs in the upper 50s
and 60s and lows in the upper 30s and 40s. A cold front assoc with
the sfc low that brought rain to the area on Sun has cleared the ern
CWA as of early this mrng. Winds have turned W/NW as the cooler air
filters into the region. Pockets of lingering light rain should push
out of the ern FA this mrng as the upper lvl trof axis swings thru.
Clouds will slowly clear from west to east but the clearing trend
will be hampered by diurnal cu/stratocu that should form on the back
edge of the clearing. Winds will be rather gusty today as the
pressure gradient tightens between the deepening sfc low across the
Grt Lks and the sfc ridge sliding to our south.

Two short waves embedded in the NW flow will affect the region thru
Wed. Sfc flow becomes SW already by tonight ahead of the first vort
max due in for Tue. The sthrly flow should allow temps to reach near
normal on Tue. A band of WWA precip is possible south of I70 on Tue
ahead of a weak bndry. Tue should be another breezy day...esp across
the nthrn half of the CWA. The second short wave approaches the
region Wed and is expected to push a reinforcing shot of cooler air
into the area behind a decent cold front Tue night. There could also be
some scttrd SHRAs assoc with this feature as well along and south of
I70 on Wed.

2%

.LONG TERM: (Thursday through Sunday)
Issued at 329 AM CDT Mon Apr 20 2015

The closed upper low is fcst to continue to slowly drift east and
is expected to be over New England by Fri. The prd starts in NW
flow but transitions to zonal by Fri as the upper low pulls away
and a weakening ridge approaches. Guidance begins to diverge
beyond this time. Both the GFS and ECMWF show the potential for
overrunning precip on Thursday. The GFS keeps most of it south of
the AR/MO border while the ECMWF has it further north across the
Ozarks. Have slight chance PoPs going from Wed night thru Thu
night to account for the model differences. The next short wave
arrives for the end of the week into the wknd and provides the
next good chance for precip. The GFS has an open wave while the
ECMWF has a closed mid level circulation so the GFS is faster mvng
the precip thru.

Regardless of the exact solution...the overall trend for cooler
temps is expected to continue thru the wknd.

2%
&&

.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1240 PM CDT Mon Apr 20 2015

SC deck remaining VFR this afternoon, then should diminish and
clear out by early this evening. Otherwise, dealing with gusty
northwest winds across the region which will diminish by early
this evening as well, but remain sustained around 10kt from the
west overnight. Then will see winds mix down to surface on
Tuesday, but not quite as gusty as today with mid cloud deck
moving in.

Specifics for KSTL:
SC deck remaining VFR this afternoon, then should diminish and
clear out by 01z Tuesday. Otherwise, dealing with gusty
northwest winds across the region which will diminish by early
this evening as well, but remain sustained around 10kt from the
west overnight. Then will see winds mix down to surface by 15z Tuesday,
but not quite as gusty as today with mid cloud deck moving in.

Byrd
&&

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

$$
WFO LSX





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