318 
FXUS63 KLSX 040430
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1030 PM CST Wed Dec 3 2025

.KEY MESSAGES...

- There is a 40-60% chance for light snow this afternoon and
  evening mainly across central and east-central Missouri and
  west-central Illinois.

- Cold temperatures return tonight and linger into Friday morning,
  potentially breaking records in Quincy, IL.

-The next best chance (20-30%) for precipitation is expected next
 weekend.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 134 PM CST Wed Dec 3 2025

Light radar returns have been plaguing the region all day. 
Forming along elevated frontogenesis with mid-level vorticity this
light precipitation has not been able to make it through the very
dry low- levels to precipitate at the surface. The exception is 
over central Missouri this afternoon where a more concentrated 
area of lift was able to produce brief precipitation at the 
surface. The surface cold front associated with the elevated 
frontogenesis currently stretches from the Kansas City metro 
northeast to the Missouri-Iowa-Illinois border. Through the 
afternoon and into the evening, column deep forcing combined with 
850-700mb frontogenesis will increase and precipitation is 
expected to become more widespread and robust. More intense 
precipitation aloft is then expected to be able to make it to the 
ground, particularly so along and south of I-70 where morning 
stratus indicated better low-level moisture. Overnight the 850-700
mb frontogenesis will wane across southeast Missouri and southern
Illinois while the cold front exits the region, bringing 
precipitation to an end.

Precipitation may briefing start as rain as dewpoint temperatures 
remain above freezing before wet bulbing occurs. Quickly though, 
rain is expected to transition to snow as the near surface 
environment cools with nightfall. Where snow is able to persist, 
up to 0.25-0.50 inches of snow is possible. In highly isolated 
locations where precipitation repeatedly tracks up to 1" of snow 
accumulation is possible. The best chances (40-60%) for 
accumulating snow are along and near I-70 where the best moisture 
and lift will overlap. 

Delia

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 134 PM CST Wed Dec 3 2025

After today's cold front, the cold morning start, and under 
continued cold air advection, temperatures on Thursday will be the 
coolest of the week. Shallow mixing and low-level temperatures in 
the negative single digits (C) will result in highs north of I-70 
below 20F and south of I-70 in the 20s to around freezing in the far 
southern portion of the CWA. Coldest low and coldest high 
temperature records are in jeopardy at KUIN tomorrow.

During the evening, a subtle mid-level disturbance aloft coupled by 
increasing low-level warm air advection will bring precipitation to 
the lower Mississippi River Valley. While a vast majority of this 
precipitation will stay to our south, I cannot rule out a brief 
period of flurries/light snow falling across far southeast Missouri 
with little to no accumulation. Warm air advection will continue 
overnight, though it's impacts won't be felt fully until during the 
day Friday when mixing can give the surface full access. 
Temperatures will be 15-20 degrees warmer on Friday with highs 
peaking in the 30s to 40s. 

During the second half of this week, a strong northern stream mid-
level low has been positioned over the Hudson Bay region, and this 
feature will continue to churn in place into the weekend. Amidst the 
cyclonic flow, a trough axis will swing through the Mississippi 
Valley this weekend, the resulting surface low moving through the 
Great Lakes and pushing a cold front through the forecast area 
Saturday. A strong surface high will develop in its wake, helping to 
pull cooler air back into the forecast area for Sunday. A clipper 
system associated with a southern stream mid-level shortwave will 
slide through the northern half of the Mississippi Valley Sunday.

Most ensemble guidance keeps the clipper and the best chances (40-
50%) for precipitation north of the forecast area, though guidance 
differs in how far south precipitation will extend. If precipitation 
does extend into the forecast area, precipitation type is expected 
to differ from north to south. Across northeast Missouri and west-
central Illinois, closest to the mass of cold air descending into 
the forecast area, confidence is highest that this precipitation 
would fall as snow. Further snow, confidence wanes in precipitation 
type as uncertainty grows in how deep the cold air will be, and 
everything from rain to a wintry mix to snow is on the table. 
Typically the precipitation footprint of these systems is on the 
smaller side, so confidence is low that we'll see precipitation 
unless the track shifts. Small changes in the path of the system and 
the depth of the cold air to the north will have implications on the 
probability, amount, and type of precipitation that falls in our 
forecast area.

By Monday, the surface high to the north of the forecast area will 
shift eastward, kicking off low-level warm air advection and pushing 
the bulk of cold air out of the region. This will continue through 
midweek, though numerous mid-level disturbances will help to keep 
cloud cover around, limiting warming. The next impactful system 
looks to be lining up for mid-week with a strong 850 low moving 
through the Great Lakes region, dragging a cold front through the 
mid-Mississippi Valley. Details on this remain uncertain, including 
if any precipitation will accompany the front.
Delia

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1024 PM CST Wed Dec 3 2025

A cold front is moving slowly southeast through the region. MVFR
ceilings will clear from northwest to southeast behind the front.
There may still be some very light snow or flurries across parts
of east central and southeast Missouri into southwest Illinois
between now and 08-09Z, however the chance for snow is only 20-30
percent. VFR flight conditions are expected to prevail after the
MVFR clears out.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX