O'Fallon, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

191
FXUS63 KLSX 141039
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
539 AM CDT Mon Apr 14 2025

.KEY MESSAGES...

-Temperatures will be 10-20 degrees cooler today than yesterday.

-Elevated fire danger is expected Tuesday across central and
northeast Missouri, and west-central Illinois.

-There are multiple chances for rain starting Wednesday and
 continuing through Sunday.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 153 AM CDT Mon Apr 14 2025

A cold front is current stretched from Clinton, MO to Mt. Sterling,
IL and will continue to scoot southeast through the forecast area
early this morning. There is a 15-20% chance of showers and
sprinkles behind the front along the 850 mb frontogenesis, which
will follow the progression of the surface boundary. Breezy
northwest winds will also persist behind the front with the highest
speeds confined largely north of the area where stronger 850 mb
winds will mix to the surface. Cold air advection along the
northwesterly flow combined with increased cloud cover will drop
temperatures between 10-20 degrees compared to yesterday, resulting
in near normal temperatures that will feel cool in comparison.

Northwesterly flow will persist Tuesday along the eastern side of an
advancing surface high. Strong cold air advection will pull 850mb
temperatures to near 0C, resulting in high temperatures closer to 60
degrees across the region. Mixing into the 850mb layer will also
bring elevated wind speeds to the surface, and breezy winds combined
with dry RH values will result in elevated fire danger across
central and northeast Missouri and west-central Illinois where fine
fuels are dry.

Delia

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 153 AM CDT Mon Apr 14 2025

The center of the surface high will track to the south of the
surface high, and the mostly clear sky and light winds will result
in the coolest night of the week with low temperatures in the upper
30s to around 40 degrees. Although Wednesday will dawn cool,
southerly flow will establish during the day as the high moves to
the east and warm air advection kicks off. A warm front will lift
north through the region during the day and warm air advection
showers in the vicinity of the front are expected from Wednesday
afternoon into Thursday. The signal for rainfall in the ensemble
guidance has decreased in coverage over the last 72 hours, with the
best chance for rain now along and north of I-70. While this area is
in need of rain, probabilities of exceeding 0.2" of rain are capped
between 30-40%. This signal has also decreased in coverage and
intensity over the last few runs.

Deep southwesterly flow will become established by Thursday and
despite precipitation and cloud cover, temperatures will continue to
increase across most of the forecast area. Southwesterly flow will
continue Friday ahead of a shortwave disturbance that will move
across the region Friday afternoon and evening. High temperatures on
Friday will be the warmest of the work week. The 25th percentile for
high temperatures ranges from the low 70s across the northern CWA to
low 80s across central Missouri, increasing confidence that much of
the area will see highs in the upper 70s to 80s.

Through the day a surface low will move from Kansas into the Great
Lakes region, eventually bringing a cold front slowly through the
forecast area overnight Friday into Saturday. The LREF joint
probabilities of MUCAPE greater than 1000 J/kg and 0-6 km shear
greater than 30 kts peaks between 60-70% along the cold front. While
these conditions are certainly favorable for strong to severe
thunderstorms, the southwest to northeast orientation of the front,
parallel deep layer shear, and tall, skinny CAPE are more favorable
for heavy rainfall than severe thunderstorms. Neither scenario is a
slam dunk. With a lack of consensus on the strength and timing of
the mid-level forcing and mesoscale details, and uncertainty
regarding the impacts of this system, we`re electing to not message
the associated SPC outlook at this time.

Temperatures will cool back to near normal for the weekend in the
wake of the cold front, which looks like it will stall somewhere
across southern Missouri and Illinois over the weekend. South of the
front, temperatures will remain warm, closer to Friday`s highs.
Additional disturbances pass through the area through the holiday
weekend, keeping the chance for showers and thunderstorms in the
forecast. Details on the location of Friday`s front and timing of
disturbances will determine where, when, and how much rainfalls over
the weekend.
Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 532 AM CDT Mon Apr 14 2025

VFR conditions are expected through the period. There is a slight
chance (20%) for light showers at UIN between 15-18Z, at COU/JEF
between 16-19Z, and at STL/SUS/CPS between 17-21Z. Otherwise winds
will be out of the northwest (290-340 degrees) throughout the
period with gusts up to 20 knots at times.

Britt

&&

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

$$

WFO LSX