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afdlsx

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
551 PM CST sun Dec 15 2019

Short term... (through late Monday night)
issued at 331 PM CST sun Dec 15 2019

Early this afternoon, a very broad-based trough extended over much of
the Continental U.S. With a west-SW flow aloft/warm air advection regime over our region. The
strong storm system that we have been watching carefully was near
The Four Corners region in the southwest Continental U.S.. at the surface,
an area of high pressure was centered over northern Illinois and
central Indiana with easterly flow over our region. A developing
surface inverted trough was poking into southwest MO. Skies were
overcast across our region. Of most note was the heavy snow band as
forecast, but this has now drifted through much of the I-70 corridor
and is looking to settle a bit more in position through early this
evening. Temperatures were in the 20s for areas near and north of I-
70 and into the low 30s for areas south of I-70.

The warm air advection snow, locally enhanced by strong frontogenesis with that
heavy snow band just north of I-70, will gradually exit this evening
being replaced by a regime exhibiting a loss of cloud ice and weak
warm air advection. In addition, the inverted surface trough will track east across
Missouri and southern Illinois and should create low level
convergence to develop areas of freezing drizzle for much of
tonight. This will continue into early Monday morning.

The main system is still expected to track east-NE through the main
flow and approach and move by our region later on Monday and into
Monday night. Lift will deepen, restore cloud ice to much of the
area, and result in an expansion of snow later on Monday morning and
continue through Monday evening before finally pulling out. The
best areas for additional snow accumulation look to be near and
north of I-70 with a snow/freezing rain scenario continuing for
areas further south. The upper level low tracks continue to favor
what looks to be an additional 2-3" of snow possible for many of the
same areas affected by the heavy snow band today.

Between the already fallen/expected snow accums and forecasted ice
accums, much of the warning/advisory stratification looks justified
and will continue with this issuance.

Tes

Long term... (tuesday through next sunday)
issued at 331 PM CST sun Dec 15 2019

The weather still looks relatively quiet for Tuesday through next
Sunday. Cold temperatures are still expected Tuesday and Wednesday
as a cold high pressure system builds into Missouri and Illinois
behind the storm...especially Tuesday night when light wind, fresh
snow and clear sky will produce excellent radiational cooling
conditions. Highs mainly in the low to mid 30s and lows in the
teens to low 20s continue to look reasonable. Wind turns back to
the south on Thursday as high pressure moves into the Ohio Valley
and further east. Widespread highs in the 40s with even some low
50s in southeast Missouri look likely with lows mainly in the 30s.
There's still a possibility of a little rain on Friday. The European model (ecmwf)
and GFS are in good agreement that a shortwave trough will move from
the Great Plains through the Midwest Friday into Friday night.
However, the GFS has a more progressive trough than the ec does.
It's also been consistently printing out very light quantitative precipitation forecast ahead of the
trough, while the European model (ecmwf) has been alternating dry-wet-now dry again.
Am keeping the forecast dry at this time as the quantitative precipitation forecast that the GFS
prints out is very light and will likely have little or no impact
even if it does rain. Saturday and Sunday continue to look dry with
highs in the 40s and lows in the 30s.

Carney

&&

Aviation... (for the 00z tafs through 00z Monday evening)
issued at 542 PM CST sun Dec 15 2019

Poor flight weather is expected across the region through the
period. Along and axis from kcou to the St. Louis Metro there
could be a mix of ptypes for the first part of this evening
including -sn, -ip, and -fzdz however the tendency as the evening
progresses should be for predominately freezing drizzle producing
light ice accumulations. At KUIN, snow will prevail until around
mid evening and the tendency should be for freezing drizzle as
well. Another round of snow will spread across the area on
Monday morning. Flight conditions will be dominated by IFR across
the region.

Specifics for kstl:

Poor flight weather is expected across the region through the
period with IFR flight conditions dominating. There could be a
mix of ptypes for the first part of this evening
including -sn,-ip, and -fzdz however the tendency as the evening
progresses should should be for predominately freezing drizzle
producing light ice accumulations. Another round of snow will
spread into the terminal around 14-15z Monday morning.

Glass

&&

Lsx watches/warnings/advisories...
MO...Winter Weather Advisory until midnight CST Monday night for
Crawford MO-Iron MO-Knox MO-Lewis MO-Madison MO-Marion MO-
Reynolds MO-Saint Francois MO-Sainte Genevieve MO-Shelby MO-
Washington MO.

Winter Storm Warning until midnight CST Monday night for Audrain
MO-Boone MO-Callaway MO-Cole MO-Franklin MO-Gasconade MO-
Jefferson MO-Lincoln MO-Moniteau MO-Monroe MO-Montgomery MO-
Osage MO-Pike MO-Ralls MO-Saint Charles MO-Saint Louis City
MO-Saint Louis MO-Warren MO.

Illinois...Winter Weather Advisory until midnight CST Monday night for
Adams Illinois-Brown Illinois-Randolph Illinois.

Winter Storm Warning until midnight CST Monday night for Bond Illinois-
Calhoun Illinois-Clinton Illinois-Fayette Illinois-Greene Illinois-Jersey Illinois-
Macoupin Illinois-Madison Illinois-Marion Illinois-Monroe Illinois-Montgomery Illinois-
Pike Illinois-Saint Clair Illinois-Washington Illinois.

&&

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