401
FXUS63 KLSX 032336
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
536 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 00z TAFs through 00z Thursday Evening)
Issued at 527 PM CST Wed Dec 3 2025

A cold front is drifting southeast through the area this evening.
VFR flight conditions ahead of the front will drop to MVFR with
ceilings falling below 2000ft and some patchy IFR ceilings as
well. There will also be bands of light snow or flurries moving
southeast behind the front which could briefly reduce the
visibility to MVFR levels. The chance for snow falls off quickly
between 06-08Z. Low ceilings are expected to clear the forecast
area slowly from north to south from late this evening through
Thursday morning.

Carney

&&

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

$$

WFO LSX