670 
FXUS63 KLSX 122358
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
558 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 00z TAFs through 00z Saturday Evening)
Issued at 541 PM CST Fri Dec 12 2025

Ceilings will remain below 2000 feet AGL through mid morning
Saturday at all of the terminals except UIN, before climbing
above 2000 feet by 14-15Z. The St. Louis area terminals will
likely see VFR ceilings by late afternoon (22Z). At UIN, snow will
likely move into the terminal by 15Z with the best chance (>90%) 
for accumulating snow between 16-20Z. IFR conditions are likely
during this time with potential for 1-3" of snowfall during the
day. Northwest winds will shift to the northeast at less than 10
knots at all of the terminals.

Britt

&&

.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