Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 111025 CCA
AFDLSX

Area Forecast Discussion...CORRECTED
National Weather Service Saint Louis MO
425 AM CST Mon Dec 11 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 334 AM CST Mon Dec 11 2017

A fair amount of weather going on thru tonight, with the main focus
being temps and winds.

Clipper evident in satellite data currently over Northern Plains
will swing southeastward today, but remain north and east of the
CWA. As has been discussed the past few days, this system has two
distinct shortwaves and associated cdfnts to impact the area today.

The first cdfnt shud arrive in the CWA by mid morning with little
more than some mid to high clouds and much higher westerly winds.
While temps will be cooler behind this fnt than ahead of it, with
temps ahead of the fnt reaching the lower 60s, the much colder air
will not arrive until tonight behind a secondary cdfnt. Have
therefore trended aoa the warmer guidance for the srn half to two-
thirds of the CWA today, and trended twd the cooler guidance for
much of the CWA tonight. Did not go too cold tonight despite a
clouds clearing out of the area as mixing shud persist thru the
night.

Have issued a Red Flag Warning thru this afternoon given the very
warm temps and low dewpoints resulting in low RH and high winds. Am
a little concerned that going forecast wind speeds are not high enuf
far enuf east and therefore, the RFW wud need to be expanded. Given
the timing of the cdfnt into central MO, do not expect changes over
that area. However, going dewpoint forecast may be too high just
behind the fnt.

Will need to monitor wind gusts this afternoon across nrn portions
of the CWA. Momentum transfer technique suggests gusts into the
35 kts range, just below wind advisory criteria. Some sites
upstream are currently seeing gusts to around 40 kts. However,
these sites are also closer to the sfc low compared to where the
low is anticipated this afternoon.

Lower clouds are expected to accompany the secondary fnt this
evening. Have held off mentioning sprinkles tonight as setup is not
great with strong gusts expected thru much of the night. Will need
to continue to monitor, but if it occurs, wud expect sprinkles and
shud occur before temps drop below freezing.

Tilly

.LONG TERM...  (Tuesday through Sunday)
Issued at 334 AM CST Mon Dec 11 2017

Colder temperatures can be expected on Tuesday due to strong
northwesterly upper level flow behind the Great Lakes upper level
trough, and as a strong surface ridge builds into our region from
the Plains.  A northwest flow shortwave will drop southeastward
through our area Wednesday afternoon and evening.  Could not rule
out a few sprinkles or flurries ahead of this feature Wednesday and
Wednesday evening, but it appears that measurable precipitation
will be east-northeast of our forecast area along and left of the
track of a surface low where more favorable moisture will exist. Low-
mid level warm air advection and surface winds backing around to a
southwest direction will lead to warmer high temperatures on
Wednesday.  Colder conditions can be expected again on Thursday and
Thursday night after the passage of a cold front, and as a
positively tilted upper level trough moves southeastward through the
region. A warming trend will begin Friday afternoon with above
normal temperatures this weekend as upper level heights rise, and
the surface wind becomes southwesterly.  The model solutions diverge
some this weekend with timing differences on the next upper level
trough and associated cold front.  The ECMWF model drops a cold
front southeastward through our forecast area Saturday night, while
the GFS was a little slower with the progression of the front. The
GFS model keeps any precipitation southeast of our forecast area,
while the ECMWF model has most of its QPF north-northeast of our
forecast area.  Will keep the forecast dry for now as this will
likely be another dry frontal passage for our area.

GKS

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1137 PM CST Sun Dec 10 2017

VFR flight conditions will prevail overnight through early Monday
afternoon with periodic waves of mid-high clouds in the northwest
flow aloft. Surface winds will be light and back to southwesterly
overnight, and then increase and becoming gusty from the west-
southwest on Monday morning as a surface trof moves east. In the
wake of the surface trof, a potent cold front will move
southeastward during the afternoon accompanied by lowering cigs
and gusty northwest winds. The gusty northwest winds will persist
into the evening. MVFR flight conditions/cigs will spread from
northwest to southeast across the area during the later afternoon
and through the evening.

SPECIFICS FOR KSTL:

VFR flight conditions will prevail tonight through Monday afternoon
with periodic waves of mid-high clouds in the northwest flow aloft.
Surface winds will be light and back to southwesterly overnight,
and then increase and becoming gusty from the west-southwest on
Monday morning as a surface trof moves east. In the wake of the
surface trof, a potent cold front will move through the terminal
in the early afternoon accompanied by lowering cigs and gusty
northwest winds. MVFR flight conditions/cigs will move into KSTL
on Monday evening with gusty northwest winds continuing.

Glass

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     59  24  37  26 /   5  10   0   0
Quincy          51  21  33  23 /  10  10   0   0
Columbia        57  23  38  26 /   5   5   0   0
Jefferson City  59  24  39  26 /   5   5   0   0
Salem           56  24  34  22 /   5  10   0   0
Farmington      62  25  38  24 /   5   5   0   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Red Flag Warning from 10 AM this morning to 6 PM CST this
     evening for Boone MO-Callaway MO-Cole MO-Crawford MO-Dent
     MO-Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Madison MO-
     Moniteau MO-Montgomery MO-Osage MO-Reynolds MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.

IL...Red Flag Warning from 10 AM this morning to 6 PM CST this
     evening for Monroe IL-Randolph IL-Saint Clair IL.

&&

$$

WFO LSX



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