Area Forecast Discussion

210
FXUS63 KLSX 010454
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1054 PM CST Sat Jan 31 2026

.KEY MESSAGES...

- After a cold night tonight, the temperature goes through some
  ups and downs over the coming week with the overall trend not
  as cold as it has been.

- Some flurries are possible on Sunday, but significant impacts
  are not expected. There`s another chance for light wintry
  precipitation on Tuesday.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 222 PM CST Sat Jan 31 2026

The surface high pressure associated with the latest cold air mass
to plague our area is moving out of the Southern Plains and toward
the Mississippi River this evening. This means we`re near the end
for this air mass. With the surface high pressure axis crossing our
region overnight tonight, we`ll have mostly calm winds and a clear
sky to allow for better radiational cooling conditions, especially
along and east of the Mississippi River. Thus in these areas we`ll
actually see temperatures near or colder than what they were this
morning. For comparison, low temperatures in central Kansas near the
center of the high last night were in the 5 to 10 below zero range.
We probably won`t get that cold as the core of the surface high is
closer to the Gulf coast and we only have a brief period of light
winds as the high pressure axis crosses the region. There`s also
some high level clouds arriving from the west by morning which
further limits the duration of ideal cooling tonight. Even so, we`re
looking at widespread lows in the single digits, with some subzero
readings most likely across Illinois and in favorable valley
locations.

After a cold start, Sunday is actually the first day of a warm up.
The cold surface high pressure axis shifts east, while upper level
ridging nudges across the Rockies and into the Plains. The leading
thrust of the warmer air aloft is being driven by a shortwave trough
tracking from the Canadian prairies toward the Great Lakes. This
spreads some snow as it moves along on Sunday, but the trough itself
weakens dramatically as it moves southeastward and the warm
advection aloft becomes more diffuse and less focused along a
frontal surface. The end result is considerably weakening lift as
this remnant wave approaches our area on Sunday. Considering it`s
still only working with remnant Pacific moisture and the forcing
weakens quickly as it arrives, the main impact for our region will
be clouds and some flurries. Both the low and high resolution
ensemble guidance have relatively similar probabilities of 0.01 QPF,
roughly 50 to 70 percent from St Louis north to Quincy. So
confidence in some flakes in the air is moderately high. But overall
QPF potential is very limited, with ensemble probability of 0.05 QPF
generally less than 20 percent. So our forecast message for Sunday
is cloudy with flurries, a minor dusting possible.

Kimble

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 222 PM CST Sat Jan 31 2026

Although Sunday`s wave initiates the warm advection, another cold
air mass lurks over the Canadian prairies waiting to head further
south. Our warming peaks locally on Monday before a cold front
Monday night brings the colder air back in. Monday has the best
potential for the temperature to warm above freezing area wide with
NBM probability of high temperature greater than 32 at 70 to 90
percent area wide. The cold front enters from the north late Monday
night and likely makes it to the southern end of our forecast area
by midday Tuesday.

Meanwhile, a southern stream shortwave trough exits the southern
Rockies and crosses the Southern Plains Monday night. Although
initially dry, this wave does hook up with some Gulf moisture as it
reaches the Mississippi Valley on Tuesday just as the cold front is
reinforcing the cold air from the north. The main questions for us
locally are how quickly does this moisture arrive and begin to
produce precipitation, and how far south is the cold air at that
point. Latest trends have been faster with the cold front, as seen
by a roughly 5 degree cooling in the NBM over the last 24 hours.
This increases confidence that if precipitation falls, it`s more
likely to be of the wintry variety. But trends have also been to
move this system a bit further east before initiating precipitation.
In a most impactful scenario, our area will be on the fringes of
this system with light precipitation just beginning as it exits to
the east. Impacts would be minor with snow the primary precipitation
type. However, there`s still plenty of potential for our region to
remain dry. LREF probability of 24 hour precipitation 0.01 or higher
peaks at only about 50 percent across our southeastern forecast area
on Tuesday which shows that more than 50 percent of guidance
actually keeps things dry.

The cold air mass pushing southward Tuesday into Wednesday is not as
cold as our recent ones, but is strong enough to send the
temperature solidly back below freezing for another 24 to 48 hours.
Dewpoints in the teens suggest that even if we were to get a clear,
calm night we`ll still be 10 to 15 degrees warmer than the peak of
our last cold air mass, with lows bottoming out around 10 degrees.

Another warm up begins on Thursday, this time with access to
considerably warmer air having built up across the Southwest US. By
Friday, NBM probability of 50 degrees rises to 10 to 40 percent
across the region. This is likely to be the first widespread above
normal day our region has seen in 3 weeks or more. However, another
cold air mass pushes quickly southward again, arriving as early as
late Friday, setting up colder conditions for this weekend. There`s
considerably more variance in the guidance on the trajectory and
duration of this cold punch, although the overall trend is for the
core of the cold to push to our east. NBM interquartile range
increases to 15 degrees this weekend indicating that variance on
just how cold it will be and for how long. For comparison, that
interquartile range is generally less than 5 degrees each day
through Thursday showing just how much greater uncertainty there is
on the weekend cold compared to any other temperature in the
forecast.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1054 PM CST Sat Jan 31 2026

A strong surface high axis is sliding across the region leading to
light and variable winds tonight. Southerly surface winds around 5-
10kts return after sunrise tomorrow along with increasing low-mid-
level clouds from the northwest. A weather system will be dropping
southeastward into the area tomorrow by the early afternoon bringing
with it lowering ceilings and a 30-50% chance for light snow
showers. Confidence is greatest (30-50%) in light snow at KUIN and
the St. Louis metro terminals during the early afternoon into the
evening tomorrow. Where the pockets light snow do occur, MVFR
visibilities are possible. Conditions are expected to improve across
the region by late tomorrow evening with surface winds going light
and variable once again.

Peine/Elmore

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion