426
FXUS63 KLSX 100000
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
600 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 00z TAFs through 00z Sunday Evening)
Issued at 538 PM CST Sat Nov 9 2024

Light to moderate rain along and east of the Mississippi River
will end slowly from west to east through the evening into the
early overnight period. Some areas of drizzle will continue to
reduce visibilities to 3SM or less at times after the steadier
rain ends, however the ceilings will be the primary contributer to
IFR flight conditions tonight. Like the rain, the ceilings will
clear from west to east through the night. VFR flight conditions
are expected to prevail for the remainder of the period once the
ceilings move out. One last weather feature to note, low level
winds will increase rapidly with height across central and
northeast Missouri late tonight, therefore expect low level wind
shear conditions in these areas from around 09Z to 13-14Z Sunday.

Carney

&&

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

$$

WFO LSX