O'Fallon, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

040
FXUS63 KLSX 302047
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
347 PM CDT Sun Mar 30 2025

.KEY MESSAGES...

- Thunderstorms, some severe, will be likely before moving out of
the area by early this evening.  Large hail of up to two inches in
diameter, damaging winds, and a few tornadoes remain the severe
weather threats.

- Strong to severe thunderstorms are possible on Tuesday night and
again on Wednesday, mainly in the afternoon and evening.

&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 345 PM CDT Sun Mar 30 2025

Severe thunderstorms continue to produce hail up to golfball size as
they move across southeast Missouri and southwest Illinois this
afternoon.  Still cannot rule out a few larger hailstones and a
tornado or two with the supercells or wind gusts to 70 mph with any
bowing segments before these storms move out of the area by 7-8 pm
with the cold front.  Then expect mainly dry weather the rest of
tonight through Monday night as a deep ridge will move into the area
as the HREF is showing high probabilities of staying dry.

It will be much cooler starting tonight with lows tonight and Monday
night mainly in the 30s and highs on Monday only in the 50s.
Confidence in these temperatures is pretty high as the NBM IQR is
only 3-5 degrees at St. Louis.

Britt

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 345 PM CDT Sun Mar 30 2025

Dry weather is still anticipated on Tuesday before we see an
increase in showers and thunderstorms on Tuesday night, particularly
north of I-70 where there will be strong moisture convergence on the
nose of an overnight low level jet.  Steep lapse rates coupled with
strong moisture transport ahead of a incoming upper trough will lead
to favorable MUCAPES for large hail late Tuesday night over parts of
northeast Missouri and west central Illinois per the latest SPC
SWODY3.

Latest cluster analysis is in better agreement in keeping the next
upper low to the north of the area on Wednesday along with the
timing of the front.  The LREF/GFS/ECMWF are showing a large
unstable warm sector ahead of the front with deep layer shear
favoring strong to severe thunderstorms.  It is unclear at this
point how much forcing will be available for the storms to form with
the upper low passing so far to the north of the area and what the
storm mode will ultimately will be.   The potential for showers and
a few thunderstorms will not clear out late week into next weekend
as the upper pattern will turn west-southwesterly behind the upper
trough. This will cause the attendant cold front to hold up just
south of the CWA keeping a chance (30-80%) of additional showers and
thunderstorms with the highest chances in southeast Missouri.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1248 PM CDT Sun Mar 30 2025

Have kept a tempo group for showers and thunderstorms in the St.
Louis metro terminals through 19Z. Any of the heavier showers or
thunderstorms could produce IFR ceilings and visibilities along
with hail and wind gusts over 35 knots. Then mainly dry weather is
expected the rest of the period with MVFR ceilings at UIN/JEF/COU
through 14-16Z before improving to VFR. There will also be a
period of VFR condition at the St. Louis area terminals this
afternoon before MVFR ceilings move into that airports tonight.
Westerly winds with gusts to 25 knots will turn to the northwest
tonight.

Britt

&&

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

$$

WFO LSX