Affton, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

319
FXUS63 KLSX 251025
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
525 AM CDT Wed Mar 25 2026

.KEY MESSAGES...

-Near record warmth on Thursday.

-Showers and thunderstorms are expected along and behind a cold
 front on Thursday, with a few storms possibly being strong to
 severe.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 350 AM CDT Wed Mar 25 2026

Another day of southwesterly low-level flow will result in
temperatures climbing into the 70s to just near 80 across the
region. The warmest temperatures will be across central, east-
central, and southeast Missouri where the influence of downsloping
off the Ozarks will add several degrees to the already warm
temperatures. During the evening a subtle mid-level shortwave will
ride through the mid-Mississippi Valley along the mid-level ridge,
bringing a few showers and thunderstorms mainly to portions of
central and northern Illinois. I cannot rule a shower or
thunderstorm making it into our far northeastern counties, but the
best chances remain outside of our area.

Delia

&&

.LONG TERM...  (Thursday through Tuesday)
Issued at 350 AM CDT Wed Mar 25 2026

On Thursday, a +3 sigma 250 mb jet streak will be located across
southern Canada with mid-level high pressure centered over western
Texas. Simultaneously, an upper level low will be ejecting east in
between the jet streak and anticyclone. As the core of the jet
streak moves east, the cold front at the surface will move south
through Iowa. Out ahead of the frontal zone, southwest winds off of
the Ozarks working in combination with compressional warming will
allow 850 mb temperatures to climb to around or just shy of 20
degrees C. Latest LREF guidance shows the IQR of the 850 mb
temperatures being only 2 degrees (19 - 21 degrees C). Generally
with this type of setup, high temperatures top out in the upper 80s
to lower 90s. Daily record high temperatures as well as all time
record high temperatures for March (see Climo Section) will be in
jeopardy.

Thursday afternoon, the cold front will sag south into Missouri with
convective initiation occurring across Indiana, Illinois, and
eastern Missouri. MLCAPE in the warm sector is forecast to be around
1500 to 2000 J/kg, however inspection of forecast soundings shows a
substantial CAP in place across Missouri and western Illinois. This
is advertised on both the NAM and GFS. Large scale forcing for
ascent is also weak at this point with only 20 m height falls
forecast, so not much in the way of thermal modification is
expected. Further east, forecast soundings show less of a CAP in
place. One potential enhancement for convection could be the upper
level low mentioned at the beginning of the long term discussion. In
particular, some guidance has this upper level low opening up and
shearing out, while other pieces of guidance still shows a jet
reflection at 250 mb with a weak area of divergence approaching
Missouri Thursday afternoon. Bulk shear vectors are forecast to be
quasi- boundary parallel with anvil level storm-relative flow
southeast. This means that upscale growth will likely happen as CI
occurs over Indiana and Illinois. Further southwest along the cold
front in Missouri, there is the potential for a more discrete mode
due to the capping inversion limiting CI. The main severe threat
will be large hail (due to an EML) with the damaging wind gust and
tornado threats being secondary. Behind the cold front, saturation
increases with elevated convection likely. Forecast soundings show
elevated instability with some storms capable of producing hail
(behind the cold front).

Temperatures then turn much colder behind the passing cold front
with highs only in the lower to mid 50s on Friday. The longwave
trough axis is then forecast to further amplify east of the Hudson
Bay on Saturday with the best ageostrophic convergence setting up
just southwest of the Great Lakes with the resultant surface high
pressure very close to northern Missouri. This will make Saturday
morning the coldest morning of the forecast period. The latest run
of the NBM is advertising areas along and north of a U.S highway 50
line with about a 50% chance of reaching or falling below freezing.

The warming trend is then set to commence on Sunday and through the
middle of the work week as mid-level heights rise over the central
United States and fall over the western United States. How fast the
mid-level ridge moves east and how strong it becomes will determine
if and when a potentially more active pattern could take shape across
Missouri and Illinois.

BAH

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 518 AM CDT Wed Mar 25 2026

VFR expected through the issuance with winds turning from the
southwest as surface high pressure rapidly moves east or away from
the region. There could be some wind gusts approaching 20 kt this
afternoon with a persistent 10kft deck across the western
terminals.

Low-level wind shear is expected to develop overnight tonight into
Thursday, though conditions are expected to be transient as the
core of the low level jet quickly progresses east overnight.

BAH

&&

.CLIMATE...
Issued at 352 AM CDT Wed Mar 25 2026

Record Highs on March 26:
St Louis   87 in 1991
Columbia   86 in 1910
Quincy     82 in 1991

All Time March High Temperature Record:
St Louis   92 on March 24, 1929
Columbia   92 on March 21, 1907
Quincy     88 on March 21, 1907


&&

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

$$

WFO LSX