661
FXUS63 KLSX 110929
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
429 AM CDT Tue Mar 11 2025

.KEY MESSAGES...

- A strong storm system will bring windy conditions and showers
  and thunderstorms to the region Friday. There remains a 15-30%
  chance for strong to severe thunderstorms Friday afternoon and
  evening.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 252 AM CDT Tue Mar 11 2025

Today`s cold front is currently draped from northern Wisconsin
through southern Minnesota to the South Dakota-Nebraska border.
Through the morning this dry front will sag southward, eventually
making it just north of the I-70 corridor by noon. Weak cold air
advection behind the front will stunt high temperatures several
degrees, keeping them in the mid 60s to low 70s. South of the front,
the warm start from overnight temperatures and robust southwest flow
will allow temperatures to warm into the mid to upper 70s. The front
will sink into southeast Missouri and southern Illinois during the
late afternoon and evening, though impacts are expected to be
minimal since we`ll be past peak heating.

The front will lift northward during the day Wednesday under another
day of south to southwesterly flow, resulting in high temperatures
in the mid to upper 70s across the region. During the day a mid-
level trough will slide along the southern US, approaching the lower-
Mississippi Valley by the evening. The weak surface reflection will
generate scattered showers and thunderstorms as it ingests Gulf
Moisture. A majority of this precipitation will stay south of the
forecast area, but I cannot rule out a stray shower or thunderstorm
making it into southeast Missouri or southern Illinois overnight, so
have left the 20-40% chance of precipitation from the NBM as is.
Delia

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 252 AM CDT Tue Mar 11 2025

At the surface Thursday will be similar to Wednesday with
southwesterly flow keeping high temperatures in the mid to upper
70s. While aloft, southwesterly mid-level flow will reestablish on
Thursday ahead of the end of week system. By Friday morning the mid-
level trough will be exiting the Four Corner`s region and will
approach the mid-Mississippi Valley by evening. A strong surface
cyclone will develop as it does so, pushing northwest of the
forecast area during the evening and overnight hours Friday into
Saturday. Ahead of this system a tight surface pressure gradient and
deep mixing will result in warm and windy conditions Friday and
Saturday. Southwesterly flow will push temperatures into the upper
70s to low 80s across the region. The primary cold front associated
with this system will slide through overnight, bringing widespread
showers and thunderstorms to the region as the system ingests Gulf
moisture.

Severe potential is certainly higher south of the Missouri-
Arkansas border where instability and moisture return are better,
but strong to severe thunderstorms remain on the table ahead of
the cold front Friday afternoon and evening. Increasing moisture
ahead of the front and the very strong 0-6 km shear (50-90 kts)
with this system will produce a conditionally favorable severe
environment. Given the strong dynamics of the system, instability
will be the limiting factor across our area as ensemble guidance
depicts a 40-60% chance of exceeding 500 J/kg of MUCAPE, with the
highest values to the east of the Mississippi River where moisture
return is best.

A secondary cold front will push through the region during the day
Saturday, driven aloft by a second mid-level shortwave that will
phase with the broader trough over the central CONUS. This second
front will bring a surge of cool air to the region Saturday, with a
reinforcing shot of cool air Saturday night as the surface low
finally ejects eastward out of the region. Highs over the weekend
will be cooler than the preceding week, with Sunday`s
temperatures the coolest of the period. Despite the 10 degree
interquartile spread in high temperatures, the 25th percentile is
near to a few degrees below normal. By the start of next work week
mid-level ridging and southwesterly surface flow will reestablish
over the forecast area, helping temperatures rebound back above
normal and setting the stage for another series of warm days ahead
of the next storm system next week.

Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 427 AM CDT Tue Mar 11 2025

Dry and VFR flight conditions will continue through the end of the
period. LLWS conditions will diminish early in the TAF period as
the LLJ shifts southeast of the terminals. A dry cold front will
drop southeast through the forecast area today. Winds will start
from the southwest and go light and variable as the front passes
before picking back up from the northeast, eventually becoming
easterly.

Delia

&&

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

$$

WFO LSX