Area Forecast Discussion

174
FXUS63 KLSX 122050 CCA
AFDLSX

Area Forecast Discussion...CORRECTED
National Weather Service Saint Louis MO
250 PM CST Fri Dec 12 2025

.KEY MESSAGES...

- Light accumulating snow is very likely (60 to 80%) to cause
  minor impacts to travel in parts of northeast Missouri and
  central/south-central Illinois yet again during the day
  tomorrow. A Winter Weather Advisory has been issued to account
  for this.

- Dangerous wind chills are expected overnight Saturday and Sunday
  morning in many areas, with very low temperatures continuing
  through Monday morning. A Cold Weather Advisory has been issued
  for these areas.

- A rapid warmup is expected Monday through Wednesday, putting a
  quick end to this round of cold air.

&&

.SHORT TERM... (Through Late Saturday evening)
Issued at 239 PM CST Fri Dec 12 2025

The primary concern during the short term remains the potential for
another round of light accumulating snow across parts of northeast
Missouri and central Illinois during the day tomorrow. Confidence in
snow accumulations and minor travel impacts has increased enough to
issue a Winter Weather Advisory for several counties in those areas.

Before we get there though, dry, chilly, but cloudy conditions
continue to grip the area in the wake of yesterday`s light snow.
Very little sun has managed to poke through this stubborn layer of
stratus, and as a result temperatures have yet to climb out of the
30s early this afternoon. While we may yet see some cloud breaks,
little change is expected through the remainder of the day.

Attention then turns to the approach of yet another clipper system,
along with a reinforcing surge of cold air. Overnight tonight, a
leading cold front is expected to sink into the northern portion of
the area ahead, bringing low level cold advection that will drop
temperatures down into the teens ahead of any developing
precipitation. By early tomorrow morning, low and mid level
frontogenesis and 500-700mb omega will slowly increase across our
northern areas ahead of the aforementioned shortwave. While there
will be a bit of mid level dry air to work through early on,
eventually the profile will saturate and snow will begin to fall
across northeast Missouri, before spreading southeast into central
and south-central Illinois through the day.

Soundings indicate that at least some saturation and lift will occur
within the dendritic growth zone, and profiles will be plenty cold
enough for snow to dominate. However, our forecast area is likely to
miss out on the most favorable overlap of forcing and
thermodynamics, and will only see a glancing blow from this round,
much like yesterday. Still, confidence in the storm track and snow
amounts has increased enough to issue a Winter Weather Advisory for
parts of northeast Missouri and central/south-central Illinois
during the day tomorrow, for amounts roughly in the 1 to 3 inch
range. This does not include the St. Louis metro area, as the snow
accumulation gradient continues to look as if it will remain to
our northeast. While we can`t rule out some light snow late in the
afternoon / early evening along the I-70 corridor, this is likely
to remain very light and impactful accumulations are unlikely
(less than 25%).

Snow will wind down shortly after sunset, and then attention turns
to the arrival of very cold temperatures and wind chills overnight
and Sunday.

BRC

&&

.LONG TERM... (Saturday night through Next Friday)
Issued at 239 PM CST Fri Dec 12 2025

Shortly after snow ends tomorrow evening, a much colder airmass will
slide into the region, causing surface temperatures to plummet. In
addition to complicating efforts to remove snow and ice from
roadways, the combination of lows in the -5 to 5 degree range, and
wind speeds in the 5 to 15 mph range, with produce wind chills
ranging from -10 to -20 degrees in many areas. There is even some
potential for even lower wind chills at times, especially in
northeast Missouri and central Illinois, if either temperatures
are slightly lower than forecast, or wind speeds slightly higher
(or both). In any case, these values will be dangerous for those
heading outdoors without proper winter attire, even for short
periods of exposure. As such, we have opted to issue a Cold
Weather Advisory Saturday night through Sunday morning for a large
portion of northeast/east-central Missouri and central Illinois,
including much of the St. Louis metro area.

Wind chills will improve enough to end the advisory during the day
Sunday, but in spite of increasing sun, temperatures may not climb
out of the teens or even single digits in some areas, and another
cold night can be expected thereafter. Temperatures and wind chills
are not expected to be quite as low Monday morning as they are
Sunday, but it will still be quite cold, and we may flirt with the
10 degree below zero advisory threshold in parts of central
Illinois.

While another weak clipper may graze the area Monday, the big story
early next week onward is that temperatures will rapidly warm back
to near, and eventually above normal as quickly as Tuesday. We
may even reach close to 60 degrees in many areas by Wednesday, so
while this cold air will not be comfortable over the weekend,
there is light at the end of the tunnel. Meanwhile, chances for
rain will increase slightly Wednesday night and Thursday, although
precipitation probabilities remain very muted in ensemble
guidance locally (20-40%), and are largely painted across the
eastern half of our area. Stay tune for more details over the next
couple of days, once we emerge from this latest round of snow and
cold.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1155 AM CST Fri Dec 12 2025

The most pressing item of concern during this TAf period is the
persistence of low clouds. MVFR to IFR conditions are currently in
place due to low stratus, and will likely persist to varying
degrees throughout the region. Some improvement is likely at UIN
later this afternoon, but this will be more muted at terminals
farther south where flight conditions may not improve beyond MVFR
levels. Late in the period, light accumulating snow is likely to
begin impacting UIN, with some visibility and ceiling reductions
expected.

BRC

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory from 9 PM Saturday to noon CST Sunday for
     Knox MO-Lewis MO-Lincoln MO-Marion MO-Pike MO-Ralls MO-
     Saint Charles MO-Saint Louis City MO-Saint Louis MO-Shelby
     MO.

     Winter Weather Advisory from 6 AM to 4 PM CST Saturday for Knox
     MO-Lewis MO.

IL...Winter Weather Advisory from 10 AM to 6 PM CST Saturday for
     Fayette IL-Greene IL-Macoupin IL-Montgomery IL.

     Cold Weather Advisory from 9 PM Saturday to noon CST Sunday for
     Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-
     Greene IL-Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe
     IL-Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-
     Washington IL.

     Winter Weather Advisory from 6 AM to 4 PM CST Saturday for Adams
     IL-Brown IL-Pike IL.

&&

$$

WFO LSX

NWS LSX Office Area Forecast Discussion