Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 041154

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
554 AM CST Sun Dec 4 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 412 AM CST Sun Dec 4 2016

Storm system moving through the Plains into the Midwest today will
provide some sloppy weather to the area.  The precip will pretty
much be all due to warm advection ahead of the shortwave today...and
the vast majority of the precip will fall as rain over our area.
However, atmosphere is dry enough in the low levels this
morning across parts of northeast Missouri and west central Illinois
that diabatic cooling will allow a change over to a rain/snow
mix...possibly going to all snow for a period.  Accumulations should
be minor as ground temperatures are well above freezing in the upper
30s and low 40s.  Some light accumulations of perhaps 1/2 inch or so
are possible on grassy and elevated surfaces in extreme northeast
Missouri and west central Illinois.  Precip will end from west to east
late this morning into the afternoon.  Highs today will depend
greatly on how long the precip lasts, but the warmest
temperatures should be across central Missouri in the low to mid 40s
and getting cooler further east where the precip lingers longer.
CWFA should be dry by 00Z tonight.  A 1020mb high pressure system
will move across the area tonight behind the storm system.  This
isn`t a particularly cold high as it`s moving up from the southwest
into our region rather from Canada.  Overnight lows will be near or
just above normal in the upper 20s and lower 30s.


.LONG TERM...  (Monday through Saturday)
Issued at 412 AM CST Sun Dec 4 2016

NAM is a bit more aggressive in bringing rain into southeast Missouri
and southwest Illinois on Monday afternoon than the GFS and ECMWF.
The global models do not bring precipitation into the area until
after 00Z ahead of a southern stream upper low that will lift out of
Texas into Mid South on Monday night.  Have cut back on the PoPs on
Monday afternoon to just the southern third of the CWA to reflect
slower entrance of the rain into the CWA.  Will keep likely or
categorical PoPs over the southeastern 2/3rds of the CWA on Monday
night as strong ascent associated with the upper trough combined
with mid level frontogenesis and low level moisture convergence will
produce widespread precipitation.  Precipitation will end quickly
from west to east on Tuesday morning as system exits quickly to the
east. Forecast soundings from the SREF and GFS suggest that
precipitation will be mainly rain, with some possibility of snow
mixing in briefly as the system exits the area.

An initial surge of cold air will move into the area behind this
system.  Dry weather is expected Tuesday night into Wednesday
morning before the GFS and ECMWF are showing the next trough moving
across the area.  While the ECWMF is depicting a stronger trough,
both are depicting enough QPF to justify keeping a chance of snow
over the area late Wednesday into Wednesday night.

Thursday and Friday still look dry and cold with 850mb temperatures
in the -10 to -15C range.  GFS is then showing another system
affecting the area by Saturday with rain/snow developing in a warm
air advection pattern.



.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 543 AM CST Sun Dec 4 2016

A storm system will spread IFR ceilings and visibilities in light
rain across the area today. Rain will mix with and become all snow
for a period over northeast Missouri and west central Illinois
this morning. Expect precipitation to end from west to east this
afternoon with flight conditions improving to MVFR before ceilings
clear out late in the afternoon into the evening. Current guidance
is hinting at fog overnight tonight. Unclear at this time how low
visibility will go, but IFR is certainly possible.


Expecting IFR ceilings in light rain and fog to move into the
terminal between 13-14Z this morning and persist through the
morning. Visibility may occasionally drop below 3 miles as well.
Cannot totally rule out a few flakes of snow this morning, but
think probability is too low to mention in the TAF at this time.
Should see rain ending during the early afternoon with ceilings
improving to MVFR. Clouds should clear out during the early
evening. Guidance continues to show fog at the terminal tonight.
Unsure at this time how low to go, so stuck with MVFR for the
current TAF.



Saint Louis     41  33  46  37 /  80   5  10  70
Quincy          37  29  45  33 / 100   0   5  40
Columbia        43  30  49  34 /  80   0  10  50
Jefferson City  45  29  50  35 /  80   0  10  60
Salem           41  33  46  38 /  80   5  10  80
Farmington      42  31  46  36 /  70   0  30  80




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