Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 022124

Area Forecast Discussion
National Weather Service Saint Louis MO
324 PM CST Fri Dec 2 2016

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 323 PM CST Fri Dec 2 2016

Two areas of clouds will affect the CWA tonight into tomorrow.
Lingering clouds to the NE continue to slowly move south through the
overnight but will gradually lift north tomorrow afternoon as system
to the SE moves into the area. Light northwesterly winds through
tomorrow morning shifting to easterly by tomorrow evening. High
clouds move into the SW CWA ahead of the next system tonight and
continue to the NE.

The timing of the cloud movements make temps a bit tricky. Light
northwest wind and possible clearing could lead to good radiational
cooling but introduction of high clouds (depending on their
thickness) could keep it in check. Went with a blend of both
scenarios for temps. Also, a few models show precip moving into the
western/southern counties of the CWA tomorrow afternoon but
soundings show that there will be dry low to mid levels. With that
in mind went with dry forecast as it will take some time to saturate
to the surface.


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 323 PM CST Fri Dec 2 2016

Rain will spread northeastward through our forecast area Saturday
night well north of a surface low centered over the southern Plains
and ahead of an approaching shortwave.  Models were depicting good
upper level divergence over our area ahead of the approaching upper
level trough moving eastward through the northern Plains and in the
right entrance region of an upper level jet streak over the Great
Lakes and Ohio Valley regions.  The highest QPF late Saturday night
and Sunday morning should be across northeast MO and west central IL
associated with the shortwave/vorticity maximum.  Although the
forecast soundings indicate mainly rain with a relatively high
freezing level, would not be surprised to see a brief period of
light snow across northeast MO and west central IL with a dusting of
snow accumulation possible on grassy areas.  Accumulation is not
expected on roads with warm road/surface temperatures.  A break in
the precipitation is expected Sunday night and Monday morning, then
rain will spread back into much of the forecast area Monday
afternoon and night ahead of a southern stream upper level trough
and associated surface low which will move northeastward through AR
and the Tennessee Valley region.  The majority of the QPF will be
across southeast MO and southwest IL in the northwestern periphery
of the surface low and will be in the form of liquid rain.  The rain
should shift east of the forecast area by Tuesday afternoon with
colder air filtering southeastward into the region as a large and
broad northern stream upper level trough moves eastward through the
northern Plains and a strong surface ridge builds southeastward into
our area from the northern Plains.  The GFS model does not have any
measurable precipitation for the rest of the extended forecast, but
the latest ECMWF model does bring a band of precipitation through
our forecast area Wednesday afternoon and night assoicated with a
shortwave and a secondary reinforcing cold front.  This
precipitation may start as rain, but would change over to snow
before ending with light snow accumulation possible.  Not real
confident with the ECMWF model solution and any accumulating snow
for our area, but am confident that the coldest air of the season so
far will impact our region beginning Wednesday night and continuing
for the remainder of the extended forecast.



.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1151 AM CST Fri Dec 2 2016

MVFR conditions expected at UIN this afternoon into portions of
tonight, with VFR conditions expected elsewhere. MVFR strato-cu deck
has arrived ahead of schedule at UIN. UIN will remain on the edge
of the better low-level moisture through this evening, thus it
will be a battle of just enough shallow mixing to scatter/lift
cloud deck to VFR or UIN remaining high-end MVFR this afternoon
all the way through tonight. Will split the difference with an
MVFR TEMPO group this afternoon, mixing out to VFR this evening
and bringing the MVFR deck back in overnight as the 850-925mb flow
turns more northerly. Otherwise, all other sites will remain VFR
through the period with generally light northwesterly winds today
turning to more easterly (but remaining light) through the day on
Saturday. Mid-level clouds will increase through the day on
Saturday as a storm system organizes out west.

Mid/high clouds will be on the increase this evening into tonight
as a storm system organizes out to the west. Winds will remain
generally light out of the northwest this afternoon into tonight,
turning more to the east and remaining light through the day
Saturday. Expect increasing mid/high cloudiness through the
period, but all cigs will remain VFR and all precip will hold off
until after the period.





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