Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 120352
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1052 PM CDT Mon Mar 11 2024

.KEY MESSAGES...

-Elevated fire danger continues across portions of the forecast area
through early this evening.

-Temperatures will climb well above normal (10-20+ degrees) today
through Thursday before returning to near normal Friday into Sunday.

-Chances for showers and thunderstorms starting tomorrow night
 (20- 40%) and continuing through early Friday. The best chance
 (60-80%) will be Thursday and Thursday night when there will also
 be the potential for a few strong to severe thunderstorms.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 215 PM CDT Mon Mar 11 2024

The mid-Mississippi Valley currently sits sandwiched
between a surface high across the Southeast US and a budding surface
low forming over eastern Colorado in response to a mid-level
shortwave edging eastward from the Four Corners Region. Elevated
winds from the tightened surface pressure gradient will persist
overnight and continue through the day tomorrow. These elevated
southwesterly winds will help keep temperatures warmer tonight than
in previous days despite the clear sky. The exception to this
will be across the southeast Missouri hollows where sheltering
will keep winds lower and encourage more efficient cooling.
Tomorrow will be another warm day in this warm air advection
regime with high temperatures pushing 15-20 degrees above normal
for mid March.

Through the day tomorrow the surface low over Colorado and the
associated mid-level shortwave will slide eastward into the mid-
Mississippi Valley, and move through the forecast area during the
evening and overnight hours. Some modest moisture return along the
southwesterly flow during the day will increase changes for
precipitation as the shortwave rolls through. The best chance for
rain will be along and north of I-70, closer to the track of the
weakening surface low. The SREF indicates a 50% chance of 250 J/kg
of MUCAPE mainly along and west of the river overnight, though some
deterministic members are indicating upwards of 500-1000 J/kg of
MUCAPE across portions of the forecast area during the same period.
Uncertainty remains in exactly how unstable the atmosphere is, which
keeps my confidence in widespread or strong thunderstorms low (<20%)
at this point. If higher instability is realized a strong
thunderstorm or two is possible and I cannot rule out some small
hail given the favorable lapse rates (7-8 C/km) and 0-6 km shear (20-
40 kts). This first round of showers and thunderstorms will kick off
an active period that will last through the work week.

MRM

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 215 PM CDT Mon Mar 11 2024

Another mid-level shortwave will move into the mid-
Mississippi Valley during the day Wednesday, with an attendant
surface low forming across the KS-OK-CO borders and strengthening as
it moves east through the day. The southwesterly flow across the
forecast area will continue Wednesday in advance of this system,
with a warm front lifting north to near the MO-IA border by the
evening. Another round of showers and a few thunderstorms (60-80%)
will move through the mid-Mississippi Valley, with the best chances
for rain along and north of I-70, closest to the warm front and mid-
level lift. Deterministic guidance indicates 400-1000 J/kg of MUCAPE
available across the forecast area overnight, while the SREF caps
probabilities of MUCAPE values >500 J/kg at 70% along and west of
the Mississippi River. Overall confidence is higher for scattered
thunderstorms in rain that falls Wednesday night into Thursday
morning. 6-7 C/km mid-level lapse rates and the long, skinny CAPE
profiles would support small hail in any thunderstorms that become a
little stronger.

The surface low will pass to our north Thursday and drag it`s
attendant cold front through the forecast area Thursday afternoon
into the overnight. Lift is largely confined to the surface and
850mb front as mid-level support is weak in the wake of the
previously mentioned shortwave. Showers and thunderstorms are
possible (70%) along this front as it shifts through the area, but
uncertainty remains in timing and intensity of the lift. If
thunderstorms are able to form, upwards of 1000 J/kg of MUCAPE
(SREF probs 70%) and 30-50 kts of 0-6 km shear will be available
to organize thunderstorms, including a few strong to severe
thunderstorms. The uncertainty with actual thunderstorm
development is likely a driving factor in keeping the forecast
area out of any SPC outlook at this time.

This system will exit the forecast area Friday morning, and dry,
northwesterly flow will keep conditions dry over the weekend with
near normal temperatures. Persistent northwest flow and the passage
of a dry cold front Sunday will bring a renewed surge of cooler air
to the region, dropping temperatures below normal for the start of
the work week.

MRM

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1047 PM CDT Mon Mar 11 2024

VFR flight conditions are expected to continue to prevail through
the period. Latest model guidance shows the low level jet just a
bit stronger over northeast Missouri and west central Illinois
than earlier runs, so will include mention of wind shear at the
KUIN terminal. Shear still looks marginal farther south and east.
Still expect the south-southwest wind to become gusty again on
Tuesday morning by 15-18Z. Could see widely scattered showers and
thunderstorms move into central/northeast Missouri during the
00-04Z Wednesday time frame, but confidence in coverage and timing
is relatively low at this time so did not include mention of
precip in the terminals.

Carney

&&

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

$$

WFO LSX


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