Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 031818
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1218 PM 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
today.

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.

Carney


.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.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1155 AM CST Sat Dec 3 2016

Surface ridge centered over IL and western KY will move eastward.
The cloud ceiling will lower tonight as an upper level disturbance
approaches with light rain spreading into the taf sites late
tonight and early Sunday morning. The rain will likely mix with
snow in UIN and possibly at the other taf sites as well as the
freezing level lowers overnight. The cloud ceiling will lower into
the MVFR catagory late tonight as the lower levels of the
atmosphere saturate, then into the IFR catagory Sunday morning.
The light rain/snow mix should change over to all rain by late
Sunday morning as the boundary layer gradually warms. Surface wind
will be weak and mainly southeasterly.

SPECIFICS FOR KSTL: Surface ridge centered over IL and western KY will
move eastward. The cloud ceiling will lower tonight as an upper
level disturbance approaches with light rain spreading into the
STL area late tonight and early Sunday morning. The rain may mix
with snow as the freezing level lowers overnight. The cloud
ceiling will lower into the MVFR catagory late tonight as the
lower levels of the atmosphere saturate, then into the IFR
catagory Sunday morning. The light rain/snow mix should change
over to all rain by late Sunday morning as the boundary layer
gradually warms. The rain should end by early afternoon with the
cloud ceiling rising back into the MVFR catagory late Sunday
afternoon. Surface wind will be weak and mainly southeasterly
through Sunday morning, then veer around to a southwest direction
Sunday afternoon.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     45  36  42  32 /   5  60  60   0
Quincy          42  33  41  28 /   5  80  80   0
Columbia        46  35  44  29 /  10  70  60   0
Jefferson City  46  36  45  30 /  10  70  60   0
Salem           45  35  41  32 /   5  50  60   5
Farmington      44  35  43  30 /  10  50  50   5

&&

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

$$

WFO LSX



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