Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 041130

530 AM CST Wed Mar 4 2015

.SHORT TERM: (Through Friday night)
Issued at 324 AM CST Wed Mar 4 2015

Rain with embedded sleet was moving across southeast MO and
southwest IL early this morning.  Starting to get a light rain and
sleet mix in the St Louis metro area.  The latest AMDARS sounding
had an elevated warm layer at 850 mb of up to 3-4 degrees C.  As the
strong surface ridge across the northern Plains builds southeastward
into our area the cold surface layer will deepen and the elevated
warm layer will shrink with time.  Much of the current precipitation
on radar will shift east of our forecast area early this morning,
but another batch of precipitation will move through southeast MO
and southwest IL, mainly south of STL late this morning and this
afternoon as a positively tilted upper level trough approaches.  The
models depict increasing upper level divergence across southeast MO
and southern IL in the right entrance region of a strong upper level
jet streak over the Great Lakes region.  The best mid level warm air
advection/isentropic lift and frontogenesis will remain across the
extreme southern portion of our forecast area today.  Precipitation
type per thickness forecasts and model forecast soundings would
suggest snow along I-70 this morning with a mix of sleet and
freezing rain across most of southeast MO and southwest IL.  By noon
there should be a mix of snow and sleet across southeast MO and
southwest IL, and by late afternoon it should be all snow.
Temperatures today will likely be nearly steady across northeast and
central MO, and slowly falling elsewhere due to strong low level
cold air advection along with low level cloud cover and
precipitation across the south or southeast half of the forecast
area.  Should get up to one tenth of an inch of ice across portions
of southeast MO this morning.  Total snow and sleet accumulations
today and tonight will range from around 1 inch in STL to near
6 inches across portions of southeast MO.  Will continue the winter
storm warning across a small portion of southeast MO and southwest
IL with a winter weather advisory extending north to almost the city
of St Louis.  Snow will linger across parts of southeast MO and
southwest IL this evening, but should shift southeast of our
forecast area late tonight as the positively tilted upper level
trough moves eastward through our area, while the strong surface
ridge continues to build southeastward into MO.  Unseasonably cold
temperatures can be expected tonight and Thursday with the models
dropping the -16 degree C 850 mb istotherm southward to around STL
bt 12Z Thursday.  The coldest temperatures Thursday night should be
across parts of southeast MO and southwest IL underneath the surface
ridge axis with good radiational cooling.  Surface winds will become
southerly across northeast and central MO on the west/northwest side
of the surface ridge Thursday night.  Much warmer temperatures can
be expected for Friday and Friday night, albeit still at least a
little below normal for early March.


.LONG TERM: (Saturday through Tuesday)
Issued at 324 AM CST Wed Mar 4 2015

Northwest flow aloft, absent any significant disturbances of note,
will dominate this period coupled with a persistent southerly flow
at the surface.  The end result will be a period of little to no
precipitation and temperatures that are at or above average for
early March, with daytime max temps in at least the 60s by early
next week.



.AVIATION:  (For the 12z TAFs through 12z Thursday Morning)
Issued at 530 AM CST Wed Mar 4 2015

Snow will move in for a few hours into the I-70 TAF locations
for a period this morning. While some erosion of the snow
currently over central-western MO is expected on its northern
side, it should still be enough to result in decent VSBY
reductions, and probably into IFR category for most. By midday or
early afternoon, the snow threat should be to the south with just
dry wx and VFR conditions the remainder of the way with a steady
wind from the north. Speaking of winds, the strongest and gustiest
winds are expected now along I-70 with the main cold push and
should diminish a bit later this morning.

Specifics for KSTL: A few flurries expected until later this
morning when the main push of snow will occur for a few hours and
will likely continue into early afternoon. VSBY reductions into
MVFR expected, and IFR a possibility depending on how well the
northern edge erodes on its approach. Otherwise, VFR and north
winds from about 19z onward.



MO...WINTER WEATHER ADVISORY until 6 PM CST this evening FOR Crawford
     MO-Jefferson MO-Washington MO.

     WINTER STORM WARNING until Midnight CST tonight FOR Iron MO-
     Madison MO-Reynolds MO-St. Francois MO-Ste. Genevieve MO.

IL...WINTER WEATHER ADVISORY until 6 PM CST this evening FOR Clinton
     IL-Marion IL-Monroe IL-St. Clair IL-Washington IL.

     WINTER STORM WARNING until Midnight CST tonight FOR Randolph IL.



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