380
FXUS63 KLSX 052358
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
558 PM CST Wed Feb 5 2025

.KEY MESSAGES...

- The northern extent of the Winter Weather Advisory was extended
  through 03z for sections of far northeast Missouri and west-
  central Illinois. The remainder of the advisory continues
  through 00z for impacts resulting from light freezing drizzle.

- To the south of the advisory, showers and a few rumbles of
  thunder will be possible through late this evening. Light rain
  may linger into early Thursday across southeastern Missouri and
  southwestern Illinois.

- Dry conditions late Thursday through Friday will be followed
  another round of precipitation late Friday through Saturday.
  Precipitation is favored to remain in liquid form

- The pattern remains active into next week with a trend toward
  cooler, seasonal temperatures next week.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 242 PM CST Wed Feb 5 2025

A weak upper level shortwave is moving overhead this afternoon as a
weak surface low tracks through southern Missouri and Illinois along
a stalling boundary. This boundary has marked the divide between sub-
freezing air over northeastern Missouri/west-central Illinois and
30s/40s over southern Missouri and Illinois. Extensive cloud cover
has inhibited much in the way of warming, though enough to pull
temperatures above freezing at most locations.

AREAS WITHIN THE WINTER WX ADVISORY: Temperatures remain near or
just below freezing over the northern stretch of Missouri into
Illinois. The upper low will provide a bit of a boost to the
coverage of precipitation before moving east tonight. Temperatures
have really struggled to warm over the northern section of the
advisory sub-freezing air hanging on in the northern couple of rows
of the advisory. The threat for freezing drizzle is expected to
continue through early this evening, while the southern section of
the advisory sees temperatures rise just above freezing. Therefore,
the northern extent of the advisory has been extended through 03z.

SOUTH OF THE ADVISORY: A brief visit of near-freezing lows that
reached just south of I-70 early this morning have since warmed
enough to limit glazing to elevated surfaces and prevent roadways
from becoming hazardous. As mentioned above, the upper shortwave
passes overhead, which enhances lift and results in broader coverage
of light rain/drizzle. SPC mesoanalysis shows a pool of 500 J/kg of
MUCAPE extending across the southern 1/3rd of Missouri. HRRR/NAM/RAP
all show significantly more MUCAPE (800-1200 J/kg) than was
projected the last couple of days, but may be slightly overdone. The
amount of CAPE is certainly capable of resulting in thunder, but the
surface layer shouldn`t be much of a factor with cool surface air
and strong capping. Showers and a few rumbles of thunder will be
possible this evening into early Thursday morning with indications
of a couple of weak impulses moving over the boundary tonight. While
the system attempts to reinforce the boundary to the south late this
evening without much success. Temperatures will be nearly steady in
the 30s/40s, if not rising slightly.

A few showers/sprinkles linger into Thursday over southern sections
of the CWA. Otherwise, surface high pressure builds in from the
central Plains with northerly flow giving enough push to position
the boundary along and south of the Missouri/Arkansas border through
Thursday night. Clouds will be pesky through the morning hours with
eventual clearing from northwest to southeast. NBM temperatures
populated highs well into the 40s to low-50s, but this is suspect
with the potential for clouds to hang on until early afternoon. The
speed/slowness of clearing will have an impact on whether we lean
toward warmer/cooler conditions. I`ve compromised with somewhere in
between, going slightly lower than NBM data with 50s confined to the
southern most sections of the CWA.


Maples

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 242 PM CST Wed Feb 5 2025

The mean upper level pattern largely remains unchanged with quasi-
zonal flow persisting this weekend into next week. This will
continue to introduce several weak shortwaves into the central U.S.
over the course of the long term period. Close attention will be
needed on the surface to mid-level evolution, which will be a
greater factor in temperatures and additional precipitation chances.

A surface boundary is projected to waffle north/south with a wide
disparity in temperatures from north to south. A surface to mid-
level ridge over the southeastern CONUS will act as a blocking
mechanism with any additional systems being driven east-northeast
around the western/northern periphery of the ridge. The greatest
uncertainty in the forecast will be Saturday as the surface boundary
remains draped somewhere across the forecast area and the next
system bring another round of precipitation. NBM data shows a
remarkable spread (20+ degrees) in the interquartile range with
respect to temperatures. The 06z ECMWF ensembles showed several
members in the 60s to low-70s along and south of I-70, while GFS
ensembles were on the cooler side. Latest 12z ECMWF now has a
limited number of 60s as far north as St. Louis but has notably
dropped a number of member suggesting anything warmer. Despite being
cooler to the north, KUIN remains above freezing with several
members in the 30s to near 40 degrees. While the temperature
forecast is less certain, the precipitation type if favored to be
all rain.

Confidence actually increases beyond Saturday as indications show
the front sinking south and bringing cooler air back into the
region. The position of the boundary will still be a factor in how
things play out next week considering a number of weaker waves are
progged to track along the boundary and introduce additional rounds
of precipitation into the forecast. While there isn`t a strong,
blockbuster system of note, troughing develops to the west and
gradual pushes eastward. The cooler theme and potential for
additional precipitation could provide opportunities for wintry
weather, but details on exactly when and where will need to wait to
be ironed out with time.


Maples

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 557 PM CST Wed Feb 5 2025

IFR flight conditions will persist through the evening at all
terminals from a combination of drizzle, fog and low stratus, and
passing showers. At KUIN, freezing drizzle could continue for
another hour as temperatures slowly rise above 32 F. Locally dense
fog cannot be ruled out, but confidence is not high in direct
impacts to any of the terminals.

A gradual improvement in flight conditions is expected overnight as
drizzle ends and winds become westerly, allowing potential areas of
scattering of the lowest ceilings (still likely remaining IFR).
However, most model guidance does not have substantial improvement
until mid/late Thursday morning into afternoon with MVFR flight
conditions giving way to VFR flight conditions as stratus lifts
slightly and scatters.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory until 6 PM CST this evening for Audrain
     MO-Boone MO-Callaway MO-Lincoln MO-Monroe MO-Montgomery MO-
     Pike MO-Ralls MO.

     Winter Weather Advisory until 9 PM CST this evening for Knox MO-
     Lewis MO-Marion MO-Shelby MO.

IL...Winter Weather Advisory until 6 PM CST this evening for Calhoun
     IL-Greene IL-Pike IL.

     Winter Weather Advisory until 9 PM CST this evening for Adams IL-
     Brown IL.

&&

$$

WFO LSX