Affton, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

459
FXUS63 KLSX 120356
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1056 PM CDT Sun May 11 2025

.KEY MESSAGES...

-Showers and thunderstorms return to much of the region Monday and
linger into Tuesday, particularly across southeast Missouri and
southern Illinois.

-Temperatures will warm through the week with the hottest
 temperatures expected on Thursday.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 135 PM CDT Sun May 11 2025

The mid-level low currently stalled over the lower-Mississippi
Valley will kick northward this evening, bringing vorticity maxima
into the forecast area by late tonight into early tomorrow morning.
These disturbances will spread showers and thunderstorms into the
forecast area from the south and east, though coverage will increase
during the afternoon with daytime heating. Despite the 1000-1500
J/kg of MUCAPE, shear is very weak and strong to severe
thunderstorms are not expected. Most locations will see less than
0.25" of rain, although thunderstorms may locally enhance rainfall.

Increased cloud cover and scattered to numerous showers and
thunderstorms will keep high temperatures stunted to near normal
tomorrow across much of the forecast area. The exception will be
portions of far northern Missouri and west-central Illinois where
precipitation and cloud cover will be more limited. Here, solar
insolation will help push temperatures to similar values as today.

Precipitation will wane Monday night as instability diminishes and
the mid-level low begins to lift northeastward into the Ohio River
Valley.

Delia

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 135 PM CDT Sun May 11 2025

By Tuesday the influence of the mid-level low will be best east of
the Mississippi River as the low moves northeastward. Diurnal
instability will further enhance scattered shower and thunderstorm
development during the afternoon. As the mid-level low exits, a mid-
level ridge will move into the mid-Mississippi Valley. This pattern
change will kick off a brief but intense warm up during an already
warm week. Southwesterly low-level flow will become established on
Wednesday, and warm air advection will push 850 mb temperatures into
the mid teens (C), resulting in high temperatures in the 80s area
wide. The warm air advection trend continues Thursday, with a low-
level warm front lifting northeast through the forecast area during
the day and pushing 850 mb temperatures into the low 20s. This is
above the 99th climatological percentile for the year, and while
unusual, confidence is high this will result in high temperatures in
the upper 80s to 90s. Instability will build across the region
during the day, and deterministic guidance indicates up to 2500-3000
J/kg of MUCAPE will develop within an environment with 40+kts of 0-
6km shear.

Meanwhile, a northern stream trough will swing from the central
Plains into the upper Mississippi Valley during the day. It will
bring a cold front through the forecast area Thursday into Friday.
Despite the instability and shear, the best forcing and moisture for
thunderstorms will remain to the north, closer to the attendant
surface low. Additionally, deterministic models indicate a strong
cap will be in place, thanks to the robust low-level warm air
advection. All of this will stunt our ability to generate showers
and thunderstorms along the front, let alone anything strong to
severe. Given that, we are continuing to not message the SPC Day 5
15% risk.

The cold front will move through the forecast area by Friday, as the
axis of the mid-level trough passes through the mid-Mississippi
Valley. Quasi-zonal flow will establish for the weekend, so while
cold air will advect into the forecast area behind the front, it
will be weak. Temperatures are expected to be cooler over the
weekend than Thursday, but the NBM 25th percentile for high
temperatures still keeps temperatures above normal for this time of
year. Additionally, the quasi-zonal mid-level flow will keep the
region open to numerous disturbances through the weekend and a
chance for showers and thunderstorms persists.

Delia

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1048 PM CDT Sun May 11 2025

MVFR ceilings will overspread southeast and east central Missouri
as well as southwest and south central Illinois beginning around
09Z and continuing through 15-17Z. Some IFR ceilings are also
likely across the higher terrain of the eastern Ozarks Monday
morning. Scattered showers will also spread to the northwest
along with the low clouds through the morning. A few waves of
scattered showers and isolated thunderstorms will continue into
the afternoon. Rain should mostly dissipate by 00Z or shortly
thereafter. MVFR ceilings are expected to improve to VFR during
the late afternoon/early evening.

Carney

&&

.CLIMATE...
Issued at 1048 PM CDT Sun May 11 2025

Record maximum temperatures and warmest minimum temperatures
for May 14 and 15.

                MAY 14      MAY 15

ST Louis:
MAXIMUM         93 2013     94 1944
WARMEST MIN     73 1915     72 2013


Columbia:
MAXIMUM         90 2022     90 1944
WARMEST MIN     67 1941     71 1941


Quincy:
MAXIMUM         94 1915     93 1944
WARMEST MIN     66 1932     69 1962



&&

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

$$

WFO LSX