Area Forecast Discussion

869
FXUS63 KLSX 291139
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
539 AM CST Sat Nov 29 2025

.KEY MESSAGES...

- A winter storm will continue to impact the area through this afternoon,
  with the greatest impacts expected across northeastern Missouri
  and west-central Illinois. A Winter Storm Warning and Winter
  Weather Advisory remain in effect for portions of the area.

- Another round of snow is forecast to impact the area Monday- Monday
  night, with a medium chance (40-60%) of an inch or more of
  snow.

- Abnormally cold temperatures are expected through the upcoming
  week.


&&

.SHORT TERM... (Through Sunday Night)
Issued at 248 AM CST Sat Nov 29 2025

Early morning water vapor imagery shows a deepening trough digging
into the Plains, with a moisture plume extending from the Gulf
northward into the Northern Plains. The trough`s surface reflection
can be seen in observations traversing the Oklahoma-Kansas state
line. Robust warm air advection ahead of the low, indicated by the
wing of precipitation moving across the area and driven by a
strengthening low-level jet, will continue to overspread the CWA as
the low pushes east-northeastward. Recent ACARS profiles upwind out
of KSGF show winds peaking at 50-55 kts between 900 and 850 mb, and
this is expected to translate eastward across our region. This will
continue to feed precipitation chances through the morning into the
afternoon across the entire CWA, with winds also picking up thanks
to mixing of the low-level jet. Wind gusts will occasionally peak
around 40 mph through the day, particularly across southeastern
Missouri and southwestern Illinois this afternoon when the core of
the jet will pass overhead.

Back to the precipitation - as expected, heavier precipitation rates,
dynamic cooling, and wetbulbing have brought temperatures north of
the I-70 corridor to or below freezing where precipitation occurs,
with most locations here reporting snow. Thanks to the strong warm
air advection, portions of central Missouri are seeing quick
fluctuations in precipitation type as the aforementioned processes
and the advection battle. As the low and low-level jet draw closer
through the day, the warm air advection will win out, with
temperatures slowly warming above freezing from southwest to
northeast, changing snow over to rain as it does so. This changeover
will gradually occur later this morning through this afternoon, with
portions of northeastern Missouri and west-central Illinois being
the last to changeover, if they do so at all.

For this portion of the area, the Winter Storm Warning remains on
track. Here, accumulations of 5"+ are expected (90% or higher chance
based on the 00z HREF). A row of counties southward in the Winter
Weather Advisory, a tight gradient is expected, and there is a low
chance that warning-criteria accumulation could sneak into northern
portions of these counties. Within the entire advisory area,
confidence in amounts is lower thanks to the effects of the warm air
advection, fracturing of ice crystals thanks to strong winds, and
compaction. On the low end, amounts within the advisory may range
from 1-3" or up to 5" on the high end. Regardless, confidence in
impacts to travel within the advisory are high (80% chance), as
snowfall rates now through approximately 8am may exceed 1" an hour
at times. This will lead to quick degradation of road conditions,
especially those untreated.

As the low-level jet pivots eastward, the more persistent
precipitation will come to an end west to east through the afternoon
and early evening. The low`s attendant cold front will quickly swing
through the CWA this evening, marking the end of precipitation
chances across the area. There may be a brief hit of snow or rain-
snow mix with this FROPA, but confidence is low that it will be
impactful. This FROPA signals the entry of an Arctic air mass
into the Midwest, with temperatures falling quickly late this
evening and tonight. Lows look to bottom out in the mid-20s for
most locations, with portions of northeastern Missouri and west-
central Illinois seeing values in the teens. For areas that
maintain snowpack into the evening, forecasted low temperatures
may need to be bumped down a degree or two.

This Arctic air mass will only move further into the region tomorrow
thanks to deep northwesterly flow in the wake of the departing upper-
level trough. Afternoon temperatures will struggle to break freezing
for a majority of locations, with Reynolds, Iron, and Madison
counties in MO having the greatest chance (50-60% per the NBM) of
reaching or exceeding 32 degrees. The current forecast (mid-20s) is
nearly 20 degrees below climatological normals. This sets the stage
for an even colder night Sunday, with teens forecasted for lows
across the entire CWA.

Elmore

&&

.LONG TERM... (Monday through Friday)
Issued at 248 AM CST Sat Nov 29 2025

Early Monday, guidance consensus is that another upper-level trough
will be quickly making its way through the central CONUS; its
surface low deepening along the Gulf Coast and moving northeastward.
While this would typically place our CWA well north of any impacts,
frontogenical forcing paired the lift via the trough axis and a
developing upper-level jet streak will be enough to force light
snowfall across the CWA Monday into Monday night. Due to ongoing
impacts from our current winter storm, an in-depth examination of
this event will have to wait. Confidence is high that totals will be
relatively light, with NBM probabilities of reaching and exceeding
1" at 40-60% area-wide but failing to rise above 30% for 2" for much
of the area. Still, this light snowfall could still be impactful if
it coincides with the evening rush hour, particularly for the St.
Louis metro area. We will be able to better hone in on this system
with this afternoon`s or tonight`s forecast package.

Beyond Monday`s system, a majority (80%+) of global ensemble members
are dry through the end of the workweek. A dry FROPA late
Wednesday/early Thursday and persistent troughing just north of the
region will reinforce our below normal temperatures, with ensemble
means supporting that most locations will fail to get out of the 30s
through the upcoming week. The coldest portion of the period looks
to be in the wake of the cold front Wednesday night and Thursday,
though ensemble spread leads to low confidence in exact values.

Elmore

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 521 AM CST Sat Nov 29 2025

Impacts will continue through the entire period at all local
terminals. This morning, snow is impacting the region, with a
gradual transition to rain from west to east through the daylight
hours. This transition to rain has already occurred at KJEF and
KCOU, though an intermittent mix is expected at KCOU for the first
couple hours of the period. At the other local terminals, the
greatest rates, and thus the lowest visibilities, are expected
through this morning.

A cold front will sweep across the region late this afternoon and
evening, bringing an end to the precipitation chances and causing
winds to shift to out of the west. This frontal passage will help
improve ceilings to MVFR, though it will likely not be until
Sunday during the day that we see widespread VFR flight conditions
return.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Storm Warning until midnight CST tonight for Knox MO-
     Lewis MO.

     Winter Weather Advisory until midnight CST tonight for Audrain
     MO-Lincoln MO-Marion MO-Monroe MO-Montgomery MO-Pike MO-
     Ralls MO-Saint Charles MO-Saint Louis City MO-Saint Louis
     MO-Shelby MO-Warren MO.

IL...Winter Storm Warning until midnight CST tonight for Adams IL-
     Brown IL-Greene IL-Macoupin IL-Montgomery IL-Pike IL.

     Winter Weather Advisory until midnight CST tonight for Bond IL-
     Calhoun IL-Clinton IL-Fayette IL-Jersey IL-Madison IL-
     Marion IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX

NWS LSX Office Area Forecast Discussion