O'Fallon, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

095
FXUS63 KLSX 221111
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
511 AM CST Sat Feb 22 2025

.KEY MESSAGES...

- Temperatures will warm up above freezing area-wide today for the
  first time in a week. Temperatures will continue to warm into
  next week. After tonight, freezing temperatures are not expected
  again until Thursday or Friday morning.

- Dry weather is expected until Wednesday/Wednesday night when
  there will be a 20-40% chance for rain.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 313 AM CST Sat Feb 22 2025

A large ridge of high pressure stretching from southern Texas
northeast through the lower Mississippi and Ohio Valleys into
southeast Canada will continue to control our weather today.  The
ridge axis will continue drifting southeast, which will bring
strengthening southwest flow at the surface to the forecast area.
Temperatures are expected to rise above freezing area-wide for the
first time in a week under the influence of this warm southwest flow
and plenty of sunshine.  Given the increasingly strong late-winter
sun and southwest flow, a 20+ degree diurnal rise is very doable and
guidance agrees with highs rising into the mid 30s to around 40 from
mid to upper teens expected just before sunrise.

While we should lose a lot of snow cover today, we probably won`t
lose all of it, particularly across the eastern Ozarks.  Winds
should weaken during the evening, especially over the eastern Ozarks
and in sheltered areas such as river valleys.  There should be
decent radiational cooling after sunset between the remaining snow
cover, relatively light winds, and a clear/mostly clear sky.
Therefore temps fall back below freezing pretty quickly during the
evening, but will likely become steady or even rise a little
overnight as the southwest flow around the ridge strengthens ahead
of the next upstream short wave.

Most of the vorticity associated with this short wave will move
across the Deep South on Sunday.  The weaker northern portion of the
wave will move across Missouri and Illinois Sunday into early Sunday
evening with little or no surface reflection.  Low level Gulf
moisture will stay locked up over the Deep South due to the blocking
surface ridge, so the wave is expected to pass with little fanfare
save some mid and high clouds. These clouds aren`t expected to be
particularly thick so there will be strong insolation once again on
Sunday, and with continuing southwest flow temperatures will quickly
rise above freezing Sunday morning and top out in the upper 40s to
low 50s.

Carney

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 313 AM CST Sat Feb 22 2025

Low level southwest flow, warm temperatures, and dry weather
continue through mid-week.  Medium range guidance continues to show
a short wave moving through the Mississippi Valley Monday night
which may produce some precip, although there`s some disagreement
on the amplitude of the wave between the deterministic GFS and
ECMWF. EOF patterns in the LREF cluster analysis also indicate
variance in the amplitude of the wave. A stronger wave, as
indicated by the ECMWF could produce a little precip across parts
of northeast Missouri/west central and south central Illinois.
However GEFS and GEPS members of the LREF are all dry in our area.
Any precip that might fall should be liquid and very light,
producing no negative impacts to the area. Will therefore continue
the dry forecast for Monday night this cycle. Temperatures are
expected to stay above freezing through this period with lows
ranging from the mid 30s to low 40s and highs in the mid 50s to
low 60s.

Guidance shows another stronger wave diving through the Plains and
into the Mississippi Valley Wednesday into Wednesday night. This
wave brings a little moisture with it and a chance for precip on
Wednesday.  The highest chance for precip with this system will be
during the day on Wednesday. Current indications are that
temperatures at the surface and aloft will be too warm for anything
but rain during this time frame, but if precip lingers into the
pre- dawn hours of Thursday morning it could get cold enough for a
little wet snow. Thursday and Friday look like the coldest days
of the week with the possibility of freezing temperatures
returning in the morning. With that said, the airmass is much
milder than the one that`s affected the are recently. While the
interquartile range of temperatures in the LREF is 6+ degrees on
Thursday and 10+ degrees on Friday, even the 25th percentile is in
the mid to upper 40s with the 75th percentile in the 55 to 60
degree range.

Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 505 AM CST Sat Feb 22 2025

VFR flight conditions and southwest winds are expected to prevail
through the period. An ceilings with bases 5000-7000 ft AGL will
move across areas generally along and south of I-70 this morning.

Carney

&&

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

$$

WFO LSX