Area Forecast Discussion
Issued by NWS St. Louis, MO

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270
FXUS63 KLSX 202033
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
333 PM CDT TUE SEP 20 2016

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 331 PM CDT Tue Sep 20 2016

Expect dry conditions tonight and tomorrow as weak front that is
currently over the northern CWA will lift northward this evening as
warm front.  Upper ridge will remain over the Midwest keeping
subsidence over the CWA.   Dewpoints are higher than they have been,
so expect lows tonight to fall to close to MOS guidance, with the
coolest readings across the Ozarks and south central Illinois. Highs
on Wednesday will climb well above normal with 850mb temperatures
in the upper teens C which supports highs around 90.

Britt

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 331 PM CDT Tue Sep 20 2016

Unseasonably warm conditions will continue due to upper level
ridging over the area and persistent southerly surface winds.  Will
leave the forecast dry Wednesday night through Thursday night,
although could not rule out a few showers/storms trying to clip
parts of northeast MO and west central IL with shortwaves
overtopping the upper level level ridge and a nearly stationary
front across the northern Plains and Great Lakes region.  The upper
level ridge will build further northward over the region on Friday
with convection shifting even further north of the forecast area.
The GFS model tries to bring a backdoor type cold front south-
southwestward into parts of west central and southwest IL on
Saturday which could lead to slightly cooler temperatures across
this area.  The ECMWF model is not as strong with the surface ridge
across the Great Lakes region and hence keeps the front northeast of
our forecast area.  For now will continue to forecast high
temperatures about 10 degrees above normal through Saturday. This
upper level ridge should should begin to shift slowly southeast of
our area as a deep upper level trough approaches the Plains.  The
ECMWF model is a little quicker bringing the upper level trough
eastward and shifting the upper level ridge southeastward as
compared to the GFS model, and also a little quicker bringing a cold
front southeastward into our area already by late Saturday night and
Sunday.  For now will lean toward the slower model solution with
only slight chance pops over much of our area Sunday. It looks like
most of the potential convection should remain northwest of STL
through Sunday night.  The model solutions diverge for the next work
week with the GFS dropping the cold front south of our forecast area
by Monday night and ending the precipitation chances, while the
ECMWF model keeps the chance of showers/storms going through the
remainder of the extended forecast due to closing off the upper
level trough near the TX and OK Panhandle region and keeping the
surface ridge over the northern Plains.  With plenty of uncertainty
will keep at least slight chance pops going for most of the area
through Tuesday.  Should have cooler temperatures for the next work
week as surface winds become northerly after passage of the cold
front.

GKS

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1244 PM CDT Tue Sep 20 2016

Dry and VFR conditions are expected through the period with mainly
light winds. Any thunderstorms that do develop this afternoon will
be too isolated to include in the TAFs at this time.

SPECIFICS FOR KSTL: Dry and VFR conditions with light winds are
expected through the TAF period.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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