Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 252357
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
557 PM CST Tue Nov 25 2014

.SHORT TERM: (Through Wednesday Night)
Issued at 348 PM CST Tue Nov 25 2014

(Tonight through Wednesday night)

Main focus will be the potential for some accumulating snow over the
region during the day on Wednesday.  Low amplitude trough currently
entering the northern CONUS will dive southeastward and strengthen
over the Plains tonight.  The GFS has shown decent run-to-run
continuity with this feature and the ECMWF has come into agreement
with it`s solution that large scale ascent will become more
widespread as the trough moves into central and northeast Missouri
toward daybreak.  At this time it appears this ascent will be
concentrated along and west of the Mississippi River between 12-18Z
and then shift east into Illinois during the afternoon.  Most of the
forecast soundings suggest this will be snow during the morning
hours when the when the low levels will be the coldest and the
ascent will be the strongest.  By nightfall, the upper trough will
be moving quickly east of the area which will cause subsidence to
set by evening.  Have just slight chances of snow going during the
evening hours over Illinois.

MOS guidance temperatures are in good agreement during this period
and generally followed.  High temperatures tomorrow will be warm
enough to cause the snow to mix with or change over to rain which
will cut back on total snowfall amounts, particularly along and
south of I-70. Did not change going snow amounts too much. Still
appears that northeast Missouri will get around 1 inch of snowfall
with lesser amounts to the south centered along the Mississippi
River.

Britt

.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 348 PM CST Tue Nov 25 2014

(Thursday and Friday)

Upper pattern will gradually flatten out and temperatures will begin
to warm back up during this period as the models are in good
agreement that surface high will pass through the area on Thursday
night.  By Friday, south to southwesterly winds will advect warmer
air into the area which bring temperatures back to normal.

(Saturday through next Tuesday)

GFS and ECMWF still agree that upper pattern will be zonal over the
weekend with a cold front moving south across the CWA on Saturday
night and Sunday. Still looks like chances for precipitation will
increase along the the front by late in the weekend as both models
show a shortwave wave trough moving through the area on Sunday
night. Then model solutions become more divergent by early next
week as the GFS is slightly more southwesterly aloft with an
approaching storm system whereas the ECMWF stays more zonal.
Temperatures ahead of the front on Saturday still look like they
will be about 10 degree above normal with 850mb temps around +10C.
Then temperatures will be closer to normal behind the front as
coldest air will not be able to come down because of the zonal
flow.

Britt

&&

.AVIATION:  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 539 PM CST Tue Nov 25 2014

The latest data continues to indicate VFR flight conditions and
dry weather tonight with clouds increasing and thickening across
the region. A northwest flow storm system will impact the area on
Wednesday with precipitation spreading in KCOU between 13-14z and
KUIN and the St. Louis area terminals between 16-17z. Temperature
structure at the onset of the precipitation suggests all snow at
KCOU and KUIN with predominately MVFR flight conditions, while
there is more uncertainty in the ptype at and KSTL/KSUS/KCPS with
snow at the onset and then mixing with rain. Flight conditions
could lower into the IFR category during the precipitation.

Specifics for KSTL:

VFR flight conditions and dry weather expected tonight through mid
morning on Wednesday with clouds increasing and thickening. A
northwest flow storm system will impact the area on Wednesday with
precipitation spreading into KSTL between 16-17z. There is some
uncertainty in the ptype, however at this time the thinking is
that we will see snow at the onset and then mixing with rain in
the afternoon. Flight conditions could lower into the IFR category
during the precipitation.

Glass

&&

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

$$

WFO LSX





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