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000
FXUS63 KLSX 091711
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1211 PM CDT Tue Apr 9 2024

.KEY MESSAGES...

- Widespread rain will impact the area Wednesday-Thursday, with a
  60- 100% chance of at least 1 inch of rain falling across
  portions of southeast Missouri and southwest Illinois.

- Temperatures will push above normal for the weekend and beyond.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 318 AM CDT Tue Apr 9 2024

A prefrontal wind shift is moving across the forecast area this
morning, a cold front on its heels. As the prefrontal wind shift
moves through the remainder of the forecast area this morning a
shortwave disturbance will slide along the MO-AR border and spawn
showers and a few thunderstorms across portions of southeast
Missouri and southern Illinois. High res guidance indicates 500-1000
J/kg of MUCAPE across this area with a sharp gradient on the
northern extent close to Farmington. The present instability
combined with 40-45 kts of effective bulk shear would support a
thunderstorm becoming strong and producing sub-severe hail. Updraft
strength is expected to be limited given the disorganized
hodographs, so despite the dynamics, storms aren`t expected to
strengthen beyond sub-severe conditions. Storms will diminish and
shift to the east mid-morning as the mid-level disturbance exits the
area.

Through the day a mid-level trough will move from the Four Corners
region into the South Central US. A surface low already across the
northern Mexico/Texas area will strengthen and push eastward ahead
of the mid-level trough. At the same time the previously mentioned
cold front will push through the forecast area today, stunting high
temperatures to near normal before stalling just southeast of the
forecast area. Rain and a few thunderstorms will increase in
coverage across the boundary during the afternoon and into the
evening. Though most precipitation will stay south of the forecast
area, I have kept 20-30% chances for precipitation across southeast
Missouri and southwest Illinois into the evening.

Overnight into Wednesday the mid-level trough and surface low will
track northeastward into the mid-Mississippi Valley by Wednesday
morning. The system will continue to move northeast and increase
rain chances across the forecast area through the day. Instability
will be very limited on the northern edge of this system, and
thunderstorm chances will be limited to isolated rumbled across
southeast Missouri and southern Illinois.

MRM

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 318 AM CDT Tue Apr 9 2024

This system will continue to strengthen overnight into Thursday, and
the tightening surface pressure gradient will result in breezy
conditions Thursday, particularly during the day when daytime mixing
will be able to mix down gusts into the upper 20s (mph). Rain will
continue as the low slowly slides northeastward Thursday, finally
exiting the forecast area overnight as the mid-level trough ejects
from the mid-Mississippi Valley. Most of the forecast area will see
at least a few hundredths of rain, though uncertainty remains in how
far north widespread rain will push on Wednesday and Thursday. The
best area will be across southeast Missouri and southwestern
Illinois where there`s a roughly 60% chance of 2" of rain and a 20%
chance of 3" of rain for the entire system.

A mid-level ridge and surface high will build into the region in the
wake of the system for the weekend and usher in a pattern change.
While temperatures will remain near normal during the workweek
thanks to cold air advection, clouds, and rain, temperatures will
push well above normal for the weekend and into the next week under
a strong warm air advection regime. The 75th percentile for high
temperatures is pushing 90 degrees into the work week! The mid-level
ridge will deamplify over the weekend, allowing the potential for
multiple disturbances to pass through the region and bring a renewed
chance for rain during the first half of the work week.

MRM

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1208 PM CDT Tue Apr 9 2024

Light northwest winds are expected to become variable this evening
before turning to the east/northeast on Wednesday as a surface low
moves into northeastern Texas. Clouds will gradually get thicker
and lower tonight into Wednesday morning, but MVFR ceilings (along
with rain shower chances) should stay to the south of the
terminals across parts of southeast Missouri and southwest
Illinois.

Gosselin

&&

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

$$

WFO LSX