Area Forecast Discussion
Issued by NWS St. Louis, MO

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762
FXUS63 KLSX 150002
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
602 PM CST Thu Dec 14 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 328 PM CST Thu Dec 14 2017

Overcast skies expected to persist through the rest of the afternoon
into the evening. A clipper will approach the area from the
northwest late tonight. A few flurries are possible as the system
moves southeast overnight into the early morning hours over parts of
northeast and north central Missouri and western Illinois.
Overnight lows are expected to be cooler than this morning`s
values due to CAA continuing over the region. Northwest winds will
veer to the southwest as the trough passes on Friday morning.
Temperatures will be warmer and than today with highs in the lower
40s.

Kelly

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 328 PM CST Thu Dec 14 2017

The pattern aloft will be quasi-zonal over the Midwest into the
medium range...bringing mild temperatures and the chance for some
precip to the region.  The longwave trof over the western CONUS is
forecast to gradually weaken through early next week, but several
strong vorticity maxima will dive into the base of the trof through
that period and eject northeast into the Great Plains.  The first
wave will impact our area on Sunday as weak low level cyclogenesis
forced by the wave turns the flow around to the south and southwest.
Guidance is printing out a widespread area of QPF greater than 0.1
inch over the Mid Mississippi Valley...an the ECMWF is actually
quite bullish with as much as .25-
.45 inch. The precip on Sunday looks like it should be all liquid
with southwest flow bringing rising temperatures to the region.

Guidance has the next wave in line moving into the region Monday
night into Tuesday...however there appears to be little low level
cyclogenesis associated with the second wave.  Low level flow stays
relatively parallel to the baroclinic zone and the mid level forcing
lags behind the deepest moisture.  The GFS does kick out some light
QPF with this feature, but the ECMWF is almost totally dry with just
a few spits of QPF.  Don`t really see a strong signal to increase
PoPs in this time period given the weak forcing and low QPF.

GFS and ECMWF diverge toward the end of the forecast.  The general
upper pattern is similar, but the GFS is slower than the ECMWF. Both
have another longwave trof developing over the western CONUS, but
the EC pushes the trof further east forcing lee side cyclogenesis
over Colorado and western Kansas Wednesday night.  The resulting
strong low moves northeast into the Midwest on Thursday and pushes a
strong cold front into Missouri during the afternoon.  The slower
GFS is less dynamic with a much weaker low drifting into the region
on Friday, but the airmass in the cold sector of the low is still
quite a bit colder in both models.  Either way, the temperatures
should be trending downward toward the end of next week.

Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 534 PM CST Thu Dec 14 2017

Dry VFR conditions will prevail for the TAF period with brief
MVFR conditions likely for the STL metro and UIN during the first
few forecast hours. Winds will shift from the northwest to
southwesterly by sunrise and becoming gusty tomorrow afternoon.
Gusts of 15-20 are possible. There is a slight chance of light
snow flurries for UIN for early morning but confidence is too low
at this point to include. Will revisit on next issuance.


SPECIFICS FOR KSTL:

Periods of MVFR are possible through this evening but VFR
conditions will prevail for the TAF period. Light northwest winds
will become gusty west winds tomorrow afternoon with gusts 15-20
kts. The entire forecast period looks to remain dry.

Walsh

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     27  43  33  58 /   5   5   0   0
Quincy          23  40  30  54 /  10   5   0   0
Columbia        26  43  32  58 /   5   0   0   0
Jefferson City  27  44  31  60 /   5   0   0   0
Salem           24  40  29  53 /   0   0   0   0
Farmington      23  43  29  56 /   0   0   0   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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