Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 141822
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1222 PM CST Thu Dec 14 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 319 AM CST Thu Dec 14 2017

Main focus thru tonight will be cloud cover, which will dictate
temps.

Low clouds currently covering the CWA are expected to push south and
west thru the morning. As they do, a thick layer of mid and high
clouds are expected to spread over the area. With ample cloud cover
expected thru peak heating and CAA continuing thru the day, have
trended temps today twd the cooler guidance. With cloud cover
anticipated to persist thru tonight, have trended twd the warmer
guidance.

However, a fair amount of uncertainty exists regarding cloud cover
thru tonight. Expect breaks in the low clouds to develop today.
While fewer breaks in the high clouds are expected, thinner spots
are very possible, allowing more heating than currently expected.
This uncertainty continues into tonight, however, this is more
uncertainty due to differences in mdl guidance. Have trended twd a
more cloudy forecast and kept mention of flurries across nrn
portions of the CWA.

Had considered removing flurries given the 00z guidance, but 06z
NAM just arriving wud suggest a chance of flurries still being
possible. Uncertainty remains how far south flurries is possible,
but kept confined to nrn counties. Otherwise, no precip is
anticipated.

Tilly

.LONG TERM...  (Friday through Wednesday)
Issued at 339 AM CST Thu Dec 14 2017

A warming trend will begin Friday afternoon due to low-mid
warm air advection with surface winds becoming southwesterly.  Much
warmer high temperatures can be expected on Saturday as an upper
level ridge shifts eastward into the central US, along with
southwesterly surface winds, and plenty of solar insolation with
little if any cloudiness.  Highs on Saturday will be around 15
degrees above normal.  Precipitation will spread northeastward into
our forecast area late Saturday night and Sunday morning with the
approach of a southern stream shortwave from the southern Plains.
Models depict relatively strong upper level divergence ahead of this
feature.  The precipitation type should be mainly liquid rain based
on the forecast soundings, although could not rule out a brief
period of snow mixed in with the rain late Saturday night and early
Sunday morning.  Most of the precipitation should shift east of the
forecast area by Sunday afternoon.  There may be patchy light
precipitation Sunday afternoon through Monday ahead of an
approaching positively tilted upper level trough.  Most of this may
be just sprinkles or drizzle.  It may get cold enough late Sunday
night that light snow or flurries will be possible across northeast
MO and west central IL.  A surface ridge will build southeastward
into our area from the northern Plains on Tuesday as northwesterly
upper level flow returns.  Temperatures, particularly daytime highs
will continue above normal Tuesday and Wednesday with little cloud
cover.  Upper level ridging and southerly surface winds will return
on Wednesday.

GKS

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1137 AM CST Thu Dec 14 2017

A mix of MVFR and VFR ceilings are currently being observed over
the region. Most areas will likely see VFR ceilings by 20z
today. There could be some pockets of MVFR that will work back
into the area from the southeast tonight ahead of the next trough
moving into north central and northeast Missouri. There will
likely be pockets of MVFR ceilings along and ahead of the trough
as it moves southeast overnight into Friday morning. Otherwise,
VFR ceilings are forecast for the remainder of the period.

SPECIFICS FOR KSTL:

VFR ceilings are currently being observed at the terminal. There
are pockets of MVFR northwest of the terminal that could make
their way to the terminal this afternoon and early this evening. A
trough pushing through the region overnight will shift wind from
northwest to southwest around 09z with a brief period of MVFR
possible before and during passage of the trough.

Kelly

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     36  28  45  33 /   0   0   5   0
Quincy          32  24  40  30 /   0  10   5   0
Columbia        36  27  44  32 /   0   5   0   0
Jefferson City  37  27  45  31 /   0   5   0   0
Salem           36  24  41  29 /   0   0   0   0
Farmington      37  27  44  29 /   0   0   0   0

&&

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

$$

WFO LSX



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