Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240412
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1012 PM CST Mon Feb 23 2015

.UPDATE:
Issued at 938 PM CST Mon Feb 23 2015

Temperatures should rebound sometime tonight with increasing
southerly winds, as well as mid deck impacting southern sections of
the CWA over at least the next 3-6 hours. I`ve messed a bit with
hourly temp trends trying to incorporate 03z temps into above
thinking. Overall, min temps should range from the single digits
below zero over some of our central IL counties, to the lower
teens over the eastern Ozarks.

Truett

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 345 PM CST Mon Feb 23 2015

Surface ridge across northern MO will weaken and shift southeastward
tonight.  This will cause the initially light surface winds early
this evening to gradually increase from a south-southwesterly
direction late tonight on the backside of the surface ridge,
especially across northeast and central MO as well as west central
IL.  The models were also depicting increasing low level warm air
advection, particularly across northeast and central MO as well as
west central IL, with rising 850 mb temperatures.  This will
lead to falling temperatures this evening, then temperatures will
become nearly steady or slowly rise late tonight, especially across
northeast and central MO and west central IL.  Temperatures should
be a little colder across the left over snow field between UIN and
STL.  Mainly just high level clouds across the forecast area
tonight, with some mid level cloudiness as well over southeast MO
and southwest IL.

GKS

.LONG TERM:  (Tuesday through Next Monday)
Issued at 345 PM CST Mon Feb 23 2015

A longwave upper TROF will persist over eastern North America thru
Friday, with a broader, flatter, more moderated and backed flow
expected for the weekend and into early next week.  As a result,
look for below average temps to continue to dominate thru the end of
the work week with a stormy period for the weekend and into early
next week.

Temps are expected to already have a running start Tuesday morning
when the sun comes up thanks to decent SW surface winds in place and
these W-SW winds will continue thru the day with decent sunshine as
well.  This will result in our warmest day of the work week Tuesday
afternoon.  The higher MAV MOS values will be a good start to
forecasting temp maxes, but similar situations and a strengthening
late February sun angle suggests going a few degs higher, especially
where little to no snow cover exists to impede the warmup.  Look for
max temps in the 40-45 range in the COU/JEF to STL corridor with
somewhat cooler values elsewhere.  A further reduction in the
snowpack will occur.

The inverted TROF scenario for late Wednesday and Wednesday night is
looking better and a bit stronger than what the models showed 24hrs
ago.  Better and more persistent WAA and frontogenesis and, on some
models, carrying into early Thursday.  Have boosted PoPs into likely
category for Wed aftn and night, with snow accums up to 2"
possible--the highest amounts in northeast MO.  Added PoPs on
Thursday but kept low for now and something to watch.

Another cold night Thursday night and day on Friday, but for now,
looks like dangerous wind chill values will not be attained.

Heading into the weekend and early next week, the pattern remains
very favorable for a significant storm system to affect the area
with what could be a prolonged period of precipitation.  The
vertical temp profiles continue to vary rather widely to result in
myriad pcpn-type presentations but consensus suggests that a wintry
mix will occur early in the system on Saturday with a transition to
a cold rain Saturday night and Sunday before ending as some snow
heading into Monday.  Storm track will be crucial as well as how
easily the cold air yields to the approaching storm system.  It may
end up being more stubborn than the models think.  Bears continued
close watching.

TES

&&

.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1000 PM CST Mon Feb 23 2015

VFR flight conditions are expected to continue across the forecast
area through Tuesday into Tuesday night. High pressure is drifting
east and wind is already starting to turn around to the south on
the western side of the high. Wind will continue to veer to the
south-southwest through the remainder of the night. Still
expecting some marginal low level wind shear across northern
Missouri and west central Illinois as winds aloft increase on the
west side of the high. Ceilings AOA 10,000 FT will persist south
of the I-70 corridor, but should break out after 12Z. Expect winds
to increase to 10-15kts with gusts to around 20kts during the morning.
A weak cold front will move into the forecast area during the late
afternoon, shifting the wind to the west northwest. Could see some
lower ceilings with the front, but it`s not clear yet whether the
clouds will be below 3,000 FT.

Specifics for KSTL:

VFR flight conditions are expected to prevail through Tuesday
into Tuesday night. High pressure is drifting east and wind will turn
around to the south on the western side of the high. Ceilings AOA
10,000 FT will persist south of the I-70 corridor, and it looks
like these clouds will just scrape by to the south of Lambert. Expect
winds to increase to 10-15kts with gusts to around 20kts in the morning.
A weak cold front will move into the area during the early
evening, shifting the wind to the west northwest. Could see some
lower ceilings with the front, but it`s not clear yet whether the
clouds will be below 3,000 FT.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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