888
FXUS63 KLSX 092028
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
228 PM CST Sat Nov 9 2024

.KEY MESSAGES...

- Light to moderate rainfall will gradually end west to east this
  evening and tonight. Locations that experience rain can expect
  another 0.2-0.3" of accumulation.

- The next chance for rain (up to 40%) comes on Wednesday as another
  front moves across the area, with confidence high (70%) that
  rain will be light.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 226 PM CST Sat Nov 9 2024

A tightly-wound upper-level trough can be seen in current water
vapor imagery rotating across the Central Plains. Ahead of this
trough, southwesterly flow is pushing through the CWA aloft, with
drier air wrapping in to an occluding surface low centered over
Nebraska. The occluding front associated with this low is sweeping
through western Missouri currently. A low-level jet has continued to
feed warm, moist air along and ahead of the front, resulting in the
continuation of scattered to numerous showers across the region this
afternoon. Despite approximately 250-500 J/kg of MUCAPE across the
region per SPC Mesoanalysis, lightning has been infrequent if not
non-existent so far today, and while with the instability it can`t
be ruled out, confidence is very low that we`ll see thunderstorms
through the remainder of the event.

As the trough continues to push eastward, the front will pass
through the CWA this evening and tonight - clearing the CWA around
sunrise Sunday morning and taking the rain chances with it. While
the rain chances will generally clear with the front, deterministic
soundings show that there could be some patchy drizzle through the
night across northeastern Missouri and west-central Illinois.

The Pacific post-frontal air mass will move into the CWA tomorrow,
with skies quickly clearing through the morning. Between the clear
skies and southwesterly winds, temperatures through the day will
actually warm by 5-10 degrees above what is occurring today, with
highs in the mid to upper 50s along and north of I-70 and in the low
60s south of I-70. The relatively drier air and clear skies will
continue into Sunday night, combining with weak winds to allow for
temperatures to cool into the low 40s to upper 30s.

Elmore

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 226 PM CST Sat Nov 9 2024

For the start of the extended period on Monday, guidance has come to
a better consensus on the evolution of the upper-level pattern.
Quasi-zonal to northwesterly flow is expected over the Middle
Mississippi Valley in the wake of the weekend trough. While subtle
differences exist in the amplitude and timing, a majority of
guidance now has a subtle shortwave moving out of the Northern
Plains into the Midwest sometime late Monday into early Tuesday.
Given the lack of robust moisture return ahead of this feature and
that a majority of guidance has it weakening as it moves into the
region, rainfall is not expected with it or its associated weak cold
front. The differences in phasing of this shortwave have
implications on the post-frontal airmass, with warmer guidance
shaving off a couple degrees for Tuesday`s highs vs Monday`s, while
cooler guidance has nearly a 10-degree drop. With either solution,
temperatures will still remain at or above normal.

In the wake of the shortwave, A longwave trough is expected to
quickly zip through the CONUS per guidance consensus. With
differences in the exact phasing of this trough, there is
uncertainty with how much forcing will be present aloft when it
passes through the Middle Mississippi Valley. A majority of guidance
has the CWA being clipped by the southern portion of the trough,
placing the better forcing further north as a cold front moves
through the region. Additionally, sufficient moisture for widespread
precipitation will not have returned to the region due to the early-
week cold fronts. Given all of this, the chance of rain tops out 30-
40% across the area on Wednesday with the passage of the front. What
rain that does fall is expected to be light in nature, with ensemble-
based probabilities toping out around 30% for accumulation reaching
or exceeding 0.20".

With the general phasing of the trough seen in guidance, the source
of the post-frontal air, and upper-level riding quickly building
into the region in the wake of the trough, ensemble guidance shows
very little impact, if any, to temperatures in the wake of the front
to end the week and start the weekend. In fact, a majority of
guidance supports values rising into the weekend, with ensemble
means running roughly 10 degrees above normal.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1100 AM CST Sat Nov 9 2024

An approaching front has brought rain to the area, producing brief
MVFR to IFR visibilities this morning. The heaviest of this rain
is expected to move away from the local terminals early in the
period, though scattered showers will still be possible through
the afternoon into the early evening. Brief drops in visibility
are possible in these showers, but given their scattered nature,
confidence in direct impacts to terminals is low right now. With
moisture pooling ahead of the front, ceilings will continue to
decrease at all local terminals from west to east through the
afternoon into the evening, with nearly all local terminals
experiencing IFR flight conditions this evening. The exception is
KUIN, though ceilings could briefly drop to IFR this evening.

As the front passes over the terminals tonight, winds will begin
to shift to the south-southwest, ceilings improve, and skies
gradually clear. The improving ceilings and clearing skies will
likely happen instantaneously, with the current timing in the TAFs
representing the best estimate. However, timing could fluctuate by
an hour or two earlier or later as clearing trends become more
apparent.

Elmore

&&

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

$$

WFO LSX