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Area forecast discussion
National Weather Service Saint Louis MO
356 am CST Fri Dec 6 2019

Short term... (through late Sunday afternoon) issued at 348 am
CST Fri Dec 6 2019

An upper level shortwave is currently passing through the region,
driving a surface trough and cold front through the mid-Mississippi
Valley. Weak warm air advection ahead of the front has resulted in light rain
across much of southern MO and Illinois. Behind the front, high pressure
is building into the northern plains, with a thin layer of low
stratus across much of the north central Continental U.S..

Northwest upper level flow will take hold across the central Continental U.S.
Today and remain in place before turning zonal on Saturday night.
The northwest flow will help drive the cold front through the region
today, with high pressure moving in behind the front. The upstream
Post-frontal low stratus will also build into the mid-Mississippi
Valley this morning and remain in place into at least the early
afternoon before mixing and advecting out of the region. The
combination of clouds and northerly winds will drop today's highs
about 15 degrees compared to what we saw yesterday.

Skies will remain mostly clear tonight, which coupled with calm
winds beneath the surface high, should allow tonight's lows to drop
into the 20s across much of the region. As low level high pressure
slides east of the area on Saturday, winds will swing around to the
south. This will draw warmer air back into the region, pushing high
temps back into the 40s and 50s on Saturday, and perhaps the 60s on
Sunday in central and southern MO.

Bsh

Long term... (sunday night through thursday) issued at 348 am
CST Fri Dec 6 2019

By Sunday evening, guidance is in consensus showing a broad upper
level trough across the western Continental U.S.. a shortwave embedded in the
flow ahead of the trough will gradually drive cyclogenesis across
the Central Plains on Sunday night. The shortwave, cyclone, and
associated cold front will push through the region on Monday, before
the parent upper trough drives a secondary shot of low-level cold
air into the region on Tuesday.

This pattern will result in a handful of impacts for the mid-
Mississippi Valley. First up, several gefs, sref, and European model (ecmwf) ensemble
members are showing precip developing in the warm, moist flow
ahead of the surface low early on Monday morning. At least a
chance of precip will then persist until the front clears the area
on Monday night, and temps may even be cool enough to generate
some light snow before the precip ends. Secondly, a tight
pressure gradient on the back side of the low will result in stiff
northerly winds on Monday night and Tuesday morning. Finally, the
most noticeable impact will be the much colder cold temps behind
the front. Blended guidance is showing high temps on Tuesday near
or just above freezing. Gefs guidance is even a tick colder, with
the mean remaining below 30 through the day on Tuesday. Lows on
Wednesday morning will be the coldest of the week, dropping into
the teens across the region. High pressure will gradually slide to
the east of the region on Wednesday, keeping things quiet and
cool through midweek.

Bsh

&&

Aviation... (for the 06z tafs through 06z Friday night)
issued at 1035 PM CST Thu Dec 5 2019

Not a lot of changes from the prev tafs. Still expect MVFR or low
VFR cigs to develop as the cold front pushes south through the
area. Winds will become northerly and increase. Winds will
diminish late Fri afternoon and into the evening. Best chances for
rain are at stl/sus/cps overnight, but do not anticipate visbys
dropping below VFR.

Tilly

&&

Preliminary point temps/pops...
Saint Louis 46 29 49 38 / 10 0 0 0
Quincy 40 24 46 36 / 0 0 0 0
Columbia 43 26 49 38 / 5 0 0 0
Jefferson City 44 26 51 38 / 5 0 0 0
Salem 48 28 47 36 / 30 0 0 0
Farmington 49 27 50 35 / 40 0 0 0

&&

Lsx watches/warnings/advisories...
MO...none.
Illinois...none.

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