153
FXUS63 KLSX 302059
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
259 PM CST Sun Nov 30 2025

.KEY MESSAGES...

- A Winter Weather Advisory is now in effect for parts of
  northeast Missouri and west central Illinois Monday afternoon
  and evening where 2-4 inches of snow is expected.

- Lesser amounts (generally 1-3 inches) of accumulating snow are
  expected across the remainder of the area late Monday afternoon
  and Monday night.

- Temperatures will remain well below normal through next week.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 254 PM CST Sun Nov 30 2025

Primary focus in the short term is another round of snow on Monday
and Monday night.  A short wave trough which is currently over the
Rockies will move east into the Great Plains by Monday morning and
phase with another wave dropping into the Dakotas.  The combined
trough continues digging southeast, moving through Missouri and
Illinois Monday night.  Deterministic guidance has been pretty
consistent over the past couple of days in developing light snow in
low level warm advection across northern Missouri into central
Illinois Monday morning ahead of the wave.  Some very light
precipitation may fall farther south, but a layer of very dry air
below 700mb which takes most of if not all day to saturate.  The mid-
level trough will be moving into Missouri by then, and forcing will
switch from warm advection to mid-level frontogenesis.  F-gen bands
sweep through the forecast area Monday night with the last of the
snow ending in south central Illinois between 07-09Z.

Forecast soundings continue to indicate the precipitation will be
all snow through the event, and that there will be a periods when
there will be lift in the dendritic growth zone.  Guidance suggests
that snow/liquid ratios will be between 14-16 to 1 and along with
the favorable mid-level forcing this suggests a snowfall that will
be efficient at accumulating.  Additionally, the ground should be
cold enough with lows tonight expected in the mid teens to low 20s
that every snowflake should stick. With all this in mind, have
issued a Winter Weather Advisory for parts of northeast Missouri and
west central Illinois from 3 PM to 9 PM Monday where it will snow
for the longest duration and will therefore accumulate the most.

I am still concerned that the f-gen bands may produce advisory-
criteria snow Monday evening, and the HREF LPMM 24 hour snow
accumulation does drop a 2-3 inch band of snow in east central
Missouri and southwest Illinois.  However this is likely influenced
by one member (HiResW-FV3) and the HREF probability of 2 inch or
greater snowfall is only 25-40 percent. The short wave is also
moving pretty quickly, which isn`t favorable for f-gen bands to sit
over any one location for extended periods of time as they might in
the deformation zone of a well-developed cold season cyclone. These
are the primary reasons we`ve limited the advisory to the
aforementioned areas.

Carney

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 254 PM CST Sun Nov 30 2025

The official forecast remains dry for Tuesday through Thursday with
below normal temperatures through the entire period. Another weak
short wave moves across the Midwest on Wednesday and a few guidance
members spit out a hundredth or two of QPF, but the NBM PoPs remain
below 20 percent for this run.  This is primarily due to a blocking
ridge along the Gulf Coast which suggests moisture return into the
Mid Mississippi Valley will be difficult.  The light QPF has been
consistent in the GFS for the past few runs though...and now the
ECMWF is showing it too.  The LREF shows 50% probabilities of
greater than 0.01 inch across northeast Missouri and west central
Illinois, though 0.05 and greater probabilities are only around 20
percent.  This could be one of those "high chance of a very low QPF"
events that the NBM does not do well with.  Yet another wave moves
across the Plains and through the Midwest Friday which could produce
another round of wintry precip.  Current guidance shows only light
QPF if it materializes at all.  Models then diverge pretty sharply
with the GFS indicating a pattern shift to zonal flow across the
CONUS by the end of next weekend while the ECMF keeps a broad but
persistent long wave trough over the country.  The LREF mean favors
broad trough however 500mb EOF patterns indicate a great deal of
variance in both the amplitude and position of said trough.  With
that in mind, our confidence in the forecast out that far is not
high.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1139 AM CST Sun Nov 30 2025

A broad area of MVFR stratus/stratocumulus with bases from
1500-2500 AGL is drifting southward this afternoon. The clouds
should continue moving south for the rest of the afternoon into
the evening, and overspread the entire forecast area by 05-07Z.
Bases are expected to rise to VFR range after 12Z Monday morning
in all areas except northeast Missouri and west central Illinois.
There ceilings may fall to IFR range by 12-15Z.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory from 9 AM to 9 PM CST Monday for Knox MO-
     Lewis MO-Marion MO-Monroe MO-Ralls MO-Shelby MO.

IL...Winter Weather Advisory from 9 AM to 9 PM CST Monday for Adams
     IL-Brown IL.

&&

$$

WFO LSX