Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 121652
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1152 AM CDT Tue Mar 12 2024

.KEY MESSAGES...

-Well above normal temperatures (15-25 degrees) will continue through
 Thursday before they return closer to normal Friday through
 Sunday.

-The chance for showers and thunderstorms begins tonight (20-50%) and
 continues through Thursday night. The best chance (60-80%) will
 be Wednesday night into Thursday night when there will be risk
 for a few severe thunderstorms.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 422 AM CDT Tue Mar 12 2024

The latest surface analysis is showing high pressure over the
southeast CONUS with a front extending from the central Plains into
the Great Lakes.  Surface winds were from the south-southwest which
was keeping temperatures mainly in the 40s.  One more dry day is
expected as the shortwave ridge will still influence our weather
today.  That will change by tonight as the shortwave trough
currently over central Rockies will move across Missouri and
Illinois tonight.  This trough will bring enough ascent and moisture
to bring a chance (20-50%) of showers and thunderstorms across the
area tonight.  RAP/NAM soundings at COU and IRK are not showing
MUCAPES increasing significantly until the storms pass through the
area, so think only small hail will be possible with these storms
tonight.

The CAMS are showing this first round of showers and thunderstorms
moving east of the area early on Wednesday morning with the trough.
There will then be a brief lull before chances increase (20-30%)
during the area as a warm front moves north into the afternoon. This
front will move into the northern Missouri by evening and stall as
the low level jet increases which will cause an overall increase in
thunderstorm coverage along and north of I-70.  Forecast soundings
from COU, IRK, and UIN are showing ample MUCAPE under deep layer
shear of 40 knots suggesting the potential for strong to severe
storms capable of producing large hail.

Temperatures today through tomorrow will be 15 to 25 degrees above
normal as 850mb temperatures will be in the 10-15C range and winds
will remain out of the south to southwest.

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 422 AM CDT Tue Mar 12 2024

The best chance for showers and thunderstorms early on Thursday
will remain over the northern CWA. Then the operational models and
the LREF continues to show a trough lifting out of trough over
the southwest CONUS which will cause the surface low to move
across northern Missouri into northern Illinois by late in the
afternoon into evening. This will also bring an attendant front
across the rest of the CWA. There has been some uncertainty with
the timing of this front the past few days, though the latest run
of the NBM shows less spread in the IQR Thursday into Friday.
SBCAPES have only increased the past few days in the LREF and are
now in the 1000- 1500 range on Thursday with deep layer shear
around 50 knots ahead of the cold front which goes along with the
latest SPC SWODY3 slight risk. There will be the risk for a few
severe thunderstorms including supercells, particularly over the
northern CWA which will be closest to the low track.

It looks now that the rain will move out of the area before Friday
morning based on the majority of the ensemble members.  The weekend
still looks mainly dry, though have added a slight chance of light
rain Saturday night as upper trough and secondary cold front will be
moving through the area.  Temperatures will be back to near normal
behind the cold front on Thursday night, but will fall back below
normal behind the weekend cold front as LREF 850mb temperatures will
drop to near -10C by Monday morning with forecast lows dropping back
below freezing over most of the CWA.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1148 AM CDT Tue Mar 12 2024

VFR flight conditions will prevail ahead of a chance (40%) for
showers and thunderstorms that will move through during the
evening tonight. Confidence is low in where exactly showers and
thunderstorms will form, so have left mention as VCSH/VCTS for
now. Winds will remain largely southerly, diminishing in speed
overnight.

MRM

&&

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

$$

WFO LSX


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