182
FXUS63 KLSX 032317
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
517 PM CST Mon Nov 3 2025

.KEY MESSAGES...

- There is a medium chance (30-50%) for rain with a cold front
  Thursday night.

- A more potent cold front over the weekend will usher in
  temperatures more typical of fall.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 233 PM CST Mon Nov 3 2025

Water vapor imagery this afternoon shows northwesterly flow over the
CWA on the eastern edge of an upper-level ridge building into the
central CONUS. At the surface, a weak cold front is draped across
the Midwest and can be seen as a dewpoint discontinuity between
I-70 and Hwy 36/I-72. With northwesterly flow weakening aloft as
the ridge further builds into the region, this front is not
expected to make much more progress southward before stalling and
lifting northward tomorrow as a warm front.

In the mean time, high pressure will begin nudging into the CWA from
the south this evening and tonight, causing winds to go mostly calm
tonight. Across southwestern Illinois and southeastern Missouri
where confidence is greatest in mostly clear skies and where the
center of the high will be closest too, there is a low chance for
patchy fog. It has been left out of the forecast for now, however,
as the strongest signal for this fog is currently just outside of
our CWA.

As the warm front lifts northward tomorrow, low-level flow will
become south-southwesterly and begin advecting warmer air into the
region. The probability of afternoon high temperatures reaching 70
degrees is 40-70% for much of the area, with mid 70s forecast for
portions of central and northeastern Missouri where the warm air
advection will be locally enhanced due to downsloping off the
Ozarks. These downsloping setups are notoriously difficult for
models to accurately resolve, and the current forecast has been
adjusted to take this into account. However, if the flow off the
Ozarks ends up being stronger than anticipated, temperatures may
warm a degree or two more than forecast and dew point a couple of
degrees lower. This would lead to RH approaching the 30-35% range
for some locations, leading to Elevated Fire Weather conditions
given the gusty winds. The potential for this threat will continue
to be monitored.

Elmore

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 233 PM CST Mon Nov 3 2025

At the start of the extended period on Wednesday, guidance consensus
is that a potent shortwave will be moving through the Great Lakes
within a broad area of troughing. This wave will push a surface
low through the Upper Midwest and an attendant cold front through
the Middle Mississippi Valley. A stubborn, expansive area of high
pressure over the Gulf states in the days ahead of the FROPA will
limit moisture return the front can access, This, combined with a
lack of upper-level forcing, will lead to a continuation of dry
conditions. Quazi-zonal flow with subtle ridging building into the
region behind this system will cause the front have a negligible
impact on surface temperatures.

Yet another shortwave is seen within guidance consensus moving
through the central CONUS Thursday into Friday, but its amplitude
varies among guidance, leading to uncertainty with the depth and
track of its surface low. The signal for some degree of moisture
return is greater with this system, and our chances for rain will
depend on the track of the low. A more northerly track relative to
the CWA will keep our rain chances lower, while a more southerly
track would lead to better lift over the CWA and favor greater rain
chances. Given the current spread in solutions, the going forecast
represents the middle ground. As with the first system discussed,
quasi-zonal flow potentially with brief, subtle ridging building
into the region in the wake of the wave will lead to little to no
impact on surface temperatures.

A final system within the extended forecast range is set to impact
the region over the weekend, and a majority of guidance has this
system packing a punch compared to the first two. The general
phasing of the upper levels is that a shortwave will ride the
southern periphery of the trough somewhere into the Great Plains
and/or Middle Mississippi Valley. While confidence is high that a
potent cold front will accompany this wave/trough, rainfall is less
certain given differences in the phasing of the trough and thusly,
the surface low. If the low is able to form and deepen at a greater
distance westward relative to the CWA, confidence in rainfall will
increase, while further east-northeastward development will lead
to lower rainfall chances. The latter is currently favored by a
majority of guidance, and is reflected in the current forecast. At
the very least, temperatures will notably drop behind the front,
with the 25th percentile of ensemble guidance (upper 50s) for
Saturday`s highs being warmer than the 75th percentile (mid 50s)
for highs on Sunday.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 514 PM CST Mon Nov 3 2025

Dry and VFR flight conditions will persist through the end of the
TAF period under a clear sky. Winds will become light and variable
overnight as a surface high passes overnight. By tomorrow,
however, winds will become southerly and increase in strength, and
gusts will reach into the low 20s (mph) across the terminals.
While winds will diminish with sunset, they will remain elevated
overnight. Low-level wind shear may develop tomorrow evening,
though details on the strength remain too uncertain to include a
mention in the TAFs at this point.

Delia

&&

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

$$

WFO LSX