537
FXUS63 KLSX 250905
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
305 AM CST Mon Nov 25 2024

.KEY MESSAGES...

- Confidence remains low (20%) in a rain-snow mix as rain winds down
  Wednesday night into Thursday morning.

- While today`s cold front will usher in more seasonable air
  through midweek, a true taste of winter will come Thursday, with
  temperatures being more typical of January into this weekend.


&&

.SHORT TERM... (Through Tuesday Night)
Issued at 303 AM CST Mon Nov 25 2024

Morning water vapor imagery shows a shortwave passing over the
Central Plains toward the Middle Mississippi Valley. At the surface,
low pressure is moving into northern Illinois, its attendant cold
front currently pushing through west-central Illinois southwestward
into central Missouri. Through today, this cold front will continue
to march east-southeastward, with temperatures gradually falling
through the day beneath mostly cloudy skies.

The post-frontal airmass will become entrenched over the region
tonight as skies begin to clear and winds weaken. The result will be
one of the coldest nights of the season thus far, with most
locations seeing temperatures bottom out in the 20s.

In the wake of today`s shortwave, flow aloft will be quasi-zonal,
quickly ushering the post-frontal high eastward and causing winds to
gradually become southerly. This will allow for temperatures to top
out around seasonal normals - mid 40s for most locations. The
southerly flow will also help temperatures Tuesday night from
dropping as low Monday night, with most locations not seeing values
below freezing.

Elmore

&&

.LONG TERM... (Wednesday through Sunday)
Issued at 303 AM CST Mon Nov 25 2024

Quasi-zonal flow is expected to continue over the Middle Mississippi
Valley through early Wednesday per guidance consensus. However, this
will be short lived, as both deterministic guidance and ensemble
clusters show a trough amplifying and digging southward across the
Midwest and eastern CONUS. This trough will send a cold front
through the region and a surface low somewhere through the Mid
South. Differences in phasing of the trough are still leading to
uncertainty in the timing of the front and track of the low.
However, low spread in ensembles for temperatures Wednesday into
Thursday show that the differences in timing of the front are not
impactful. As for the low, global ensembles have begun to converge
on a common solution, with the low tracking south of the CWA through
the Mid South and its precipitation shield being focused more south
and east of the CWA. Rain chances (40-70%) will overspread the CWA
Wednesday afternoon into the evening, with precipitation coming to
an end through the day Thursday. Guidance has also been trending a
little warmer with temperatures during the low`s passage, resulting
in less snow showing up in ensembles. Therefore, confidence
continues to increase that a majority of the precipitation
associated with this system Wednesday into Thursday will be rain,
with some wet snow flakes mixing in as precipitation winds down
Thursday.

The main story with this trough and surface system will be the post-
frontal airmass, providing the area with the first taste of winter
this season as temperatures will be more typical of January starting
Thursday. Ensembles are clustering around high temperatures failing
to get out of the 30s for most locations Friday and Saturday with
lows in the 20s.

Guidance diverges in the upper-level pattern during the latter part
of the weekend into early next week. The main implication of this is
the potential for a reinforcing shot of cold air. While the majority
of guidance has northwesterly flow persisting over the Midwest
through early next week, guidance differs on the phasing of a
shortwave Saturday into Sunday. A stronger shortwave would bring
colder air and the potential for light snow to the CWA, while a
weaker shortwave would have less impact on temperatures and lower to
no precipitation chances. The current NBM and our forecast favors
the stronger shortwave, but fluctuations to this portion of the
period are likely in the coming days as guidance converges on a
common solution.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1021 PM CST Sun Nov 24 2024

A cold front will move through the region late tonight through
early Monday morning. Winds will veer from the south to the
northwest behind this boundary, and become gusty on Monday. These
gusts should subside by early evening. A few sprinkles or very
light rain showers may accompany this front, but probabilities are
too low to mention at any of the terminals. Any rain that does
occur looks very light, and should not reduce visibilities. There
are increasing probabilities for MVFR stratus late tonight
along/behind the front. Ceilings for the most part will be between
2000-3000 feet AGL, but a brief period with ceilings around 1500
feet AGL is possible. Low stratus is forecast to advect out of the
area off to the southeast on Monday.

Gosselin

&&

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

$$

WFO LSX