Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262346
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
546 PM CST Sun Feb 26 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 305 PM CST Sun Feb 26 2017

Southerly flow on the west side of a large high pressure system over
the southeast CONUS is forcing low level warm advection over the
area this afternoon.  This warm advection is producing light
precipitation over parts of southwest and south central
Missouri...but very dry air left in the wake of the high pressure
system is eating into the precip over our area.  That being said,
RADAR is showing some decent reflectivity approaching 35 dBZ in some
of the bands across southern Missouri and short range guidance
suggests that the warm and moist advection will continue through the
evening.  Precipitation is reaching the ground around Lake of the
Ozarks and Rolla at this time, so if the atmosphere can moisten up
enough this evening, some light rain or sprinkles continues to be
possible along and south of I-70.  Evaporative cooling may allow
some of the precip to reach the ground in a frozen state for a short
period as either light sleet or light snow.  Most of the precip
should be done by 06-08Z, except possibly some lingering sprinkles
across southeast Missouri.  Lows tonight should be around 5 to 10
degrees warmer than last night due to cloud cover and continuing
southerly flow.

Current thinking is that an area of low clouds will cover much of
southern and east central Missouri as well as southwest into central
Illinois on Monday morning.  These clouds may take a while to
scatter out on Monday, but I think much of the area will see some
sunshine Monday afternoon.  This should allow temperatures to warm
further  than today with highs likely edging to near 60 along and
west of the Mississippi...slightly cooler in the mid to upper 50s
further east.

Carney

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 305 PM CST Sun Feb 26 2017

An active pattern stil looks likely for the first half of the work
week per latest model guidance. The warm front will likely be just
along or north of the MO/IA line on monday night. This coupled with
cloudy skies and a respectable LLJ will lead to warm overnight lows.

The day on Tuesday could be quite warm with highs that could either
be at or break record high temperatures on the day Tuesday. There is
though a question on just how thick mid and high clouds will be
during the day. If clouds in the mid and high levels are thick
enough this will likely keep temperatures from breaking record
values. challenge or break record values. This will likely be within
a couple of degrees of high minimums over the area. The front and
attendant cold front will likely enter the area just at or after 12z
Tuesday morning. A couple of showers along the boundary can not be
ruled out Tuesday morning. A combination of deep layer moisture,
steep lapses rates, and daytime heating will result in a broad
unstable warm sector early Tuesday afternoon.

The convective evolution is a bit uncertain still at this time. It
appears there is a weak elevated cap on the GFS across C/NE MO and
WC IL. A look at shear profiles at this time support a mixed storm
mode with upscale growth of storms. The mode over the southern 1/3
of the CWA where deeper moisture and better shear profiles per
latest guidance would be more supportive environment for supercells.

The main threats during the day tuesday into the overnight wednesday
will be damaging winds, large hail, and perhaps a tornado in the
southern 1/3 of the CWA. The remainder of the forecast period from
Wednesday afternoon through early next weekend will be relatively
dry with northwest flow setting up over the area. Temperatures will
be at or just above seasonal values.

Kelly
&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 541 PM CST Sun Feb 26 2017

VFR conditions to persist through first part of forecast period
with diminishing south winds. Precipitation from system to our
south is struggling to make it into TAF sites, so kept VCSH
mention for metro area tafs this evening. Otherwise, as system
lifts northeast, could still see MVFR cigs towards daybreak in
metro area. Kept MVFR cigs from 12z to 16z Monday for metro area.
Otherwise, light southeast to south winds to pickup a bit by mid
morning on Monday.

SPECIFICS FOR KSTL:
VFR conditions to persist through first part of forecast period
with diminishing south winds backing to the southeast. Precipitation
from system to our south is struggling to make it into metro area,
so kept VCSH mention through 06z Monday. Otherwise, as system
lifts northeast, could still see MVFR cigs towards daybreak in
metro area. Kept MVFR cigs from 12z to 16z Monday for metro area.
Otherwise, light southeast winds to pickup a bit and become
southerly by 16z Monday.

Byrd
&&

.CLIMATE...
Record Temperatures For Tuesday 2/28

Record Highs    Record High Lows

STL 80/1972     STL 54/1895
COU 75/1972     COU 52/1895
UIN 68/1932     UIN 40/1987

&&

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

$$
WFO LSX



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