Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 061704

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1104 AM CST Tue Dec 6 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 407 AM CST Tue Dec 6 2016

There is a band of light rain currently over the southern part
over the CWA from southeast Missouri into into southwest Illinois.
This band is occurring in the deformation zone of the upper low
currently moving south of the area. This band of the rain will move
quickly out of the area this morning as the upper low lifts into the
Ohio Valley.

Areas of fog have developed over central Missouri early this
morning.  Will include the mention of fog through mid morning. Drier
air will work in from the west later this morning and do expect
partly to mostly skies over the air by afternoon.  With the cloudy
and cool start, went with highs below MOS guidance which is closer
to the SREF mean temps.

High pressure will move into the area tonight, but clouds will begin
to move back in ahead of the next system.  Lows tonight will be
close to SREF mean temps.


.LONG TERM...  (Wednesday through Monday)
Issued at 407 AM CST Tue Dec 6 2016

Primary concern for Wednesday and Wednesday night continues to be
the chance for snow as a strong shortwave dives across the Great
Plains into the Mississippi Valley.  Models have been pretty
consistent with the synoptics of this feature, but the mesoscale
forcing and available moisture hasn`t been very consistent, either
across models or run-to-run.  This engendering a lot of confidence
in the QPF from any model.  GFS has been most consistent with this
system so far, with very light QPF spreading across west central
into parts of central Missouri Wednesday afternoon in response to
strong frontogenesis from 925-700mb.  Moisture is still the limiting
factor for our CWFA.  Forecast soundings only show a brief window of
saturation during the late afternoon and early evening.  Looks like
a good deal of the the frontogenetical forcing will be in the
dendritic growth zone so if any snow does reach the ground it
could briefly accumulate quickly. Still, given the uncertainties
(now the 06/00Z ECMWF has barely any QPF in our area) think mid-
high chance remains an appropriate PoP for this situation.

Arctic high will continue building across the Great Plains and
Midwest Thursday and Friday.  Coldest temperatures of the season
still forecast for Thursday and Friday under the influence of this
high.  Daytime highs will struggle into the mid and upper 20s and
overnight lows will dip into the low and mid teens.

Medium range guidance diverges toward the end of the forecast.  The
ECMWF is more zonal than the GFS going into Saturday night while the
GFS advertises a decently sharp and fast moving shortwave moving off
the Rockies Saturday night forcing lee-side cyclogenesis over the
Plains. Resulting warm advection precip begins over the CWFA
Saturday night and precip continues through Sunday evening until the
cold front associated with the The ECMWF is slower and weaker with
the system. Subsequently the precip is delayed until Sunday morning
and lasts into Monday.  Stuck close to ensemble guidance given lack
of model agreement.



.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1057 AM CST Tue Dec 6 2016

Low pressure over central KY will continiue to move northeast.
Strong cold front will make its way across the region today
ushering in colder air. Mix if IFR/MVFR will be swept away by the
front. Gradual clearing from NW to SE this afternoon, then VFR,
with some gusty northwest wind.

SPECIFICS FOR KSTL: Have pretty much followed CONSHORT model with
VFR at 21z, which seems reasonable bases on satellite trends.
Northwest wind looks to be a little more gusty than previous
forecast. VFR or the latter part of the forecast.



Saint Louis     42  27  39  20 /   0   5  20  20
Quincy          39  22  32  16 /   0  10  10  10
Columbia        41  23  34  15 /   0   5  20  30
Jefferson City  43  25  37  17 /   0   5  20  30
Salem           43  27  39  21 /   5   0  10  20
Farmington      44  26  40  20 /   0   0  10  20




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