Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 031138

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
538 AM CST Sat Dec 3 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 432 AM CST Sat Dec 3 2016

Cool high pressure at the surface over Missouri and Illinois will move
eastward today ahead of a trof of low pressure which will deepen over
the Great Plains.  Mid and high level clouds are already
overspreading the area from the southwest as the flow aloft becomes
more southwesterly ahead of the trof.  Expect temperatures to be
about 3 to 5 degrees cooler today than they were Friday.
This is partly due to the cooler airmass associated with the high
pressure, in addition to less insolation due to more cloud cover

Warm advection increases tonight ahead of the trof.  Light
precipitation currently over Kansas, Oklahoma, and Arkansas will
move up into southern and western Missouri by late this afternoon,
and into central and northeast Missouri by late evening.
Precipitation will overspread the rest of the area during the
overnight hours.  There will likely be at least a brief mixture of
rain and snow across much of the area...but accumulating snow is
unlikely in most areas due to light precip intensity and most of the
lift being in the supercooled water droplet temperature range rather
than in the ice crystal bearing range.  Additionally, ground
temperatures are very warm in the low to mid 40s.  Parts of
northeast Missouri and west central Illinois might see a dusting to
a couple of tenths of an inch on grassy areas and elevated surfaces.



.LONG TERM...  (Sunday through Friday)
Issued at 432 AM CST Sat Dec 3 2016

GFS and SREF forecast soundings are still showing that rain will mix
with or changeover to snow, particularly along and north I-70 on
Sunday morning.  There will be enough ascent and low-mid level
moisture convergence for some minor accumulations, mainly on grassy
surfaces.  The precipitation will end from west to east late Sunday
morning and afternoon as the upper trough moves off to the east of
the CWA by mid afternoon.

A dry forecast still looks good for Sunday night into early Monday
as a surface high moves across the area.  The GFS and ECMWF are not
as aggressive on Monday afternoon in bringing rain into the area, so
have lowered PoPs over the southern CWA.  Monday night still looks
like when both the GFS and ECMWF bring a southern stream upper low
across the Mid South that will bring likely or categorical PoPs to
the southeastern half of the CWA.  Some snow will mix in with the
rain over the northwest half of the CWA on Tuesday morning before
the system moves off into the Ohio Valley.

A strong cold front will move through the area on Tuesday night
which will bring below normal temperatures to the area for the end
of the week. A weak storm system behind the front will bring a
chance of snow to the area on Wednesday and Wednesday night.  850mb
temperatures by next Friday will be in the -10 to -15C range.



.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 525 AM CST Sat Dec 3 2016

VFR flight conditions with east-southeast flow are expected to
prevail today and into the evening as low level high pressure
moves east of the area. A trof of low pressure over the Great
Plains will move into the eastern Great Plains tonight spreading
moisture and light precipitation into the area ahead of it. Most
of the precipiation is expected to be rain, but it will mix with
snow at times especially during the pre-dawn hours of Sunday
morning. (The exception will be northeast Missouri and west
central Illinois where more snow is likely. MVFR conditions in
the light mixed precipiation are likely across most of the area by
12Z Sunday.


Expect VFR flight conditions to prevail at Lambert at least
through the evening and most of the overnight hours as well.
Ceilings will be lowering and thickening through the period ahead
of a storm system moving into the area from the Plains. Light
rain is expected to develop after 06Z and the rain should mix with
a little light snow around 12Z Sunday morning. The mix of rain and
snow will likely bring flight conditions down to MVFR.



Saint Louis     45  36  42  32 /   5  60  60   5
Quincy          42  33  41  30 /   0  80  80   5
Columbia        46  35  44  30 /  10  70  60   5
Jefferson City  46  36  45  31 /  10  70  60   5
Salem           44  35  41  32 /   5  50  60   5
Farmington      44  35  43  31 /  20  50  50   5




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