Area Forecast Discussion

740
FXUS63 KLSX 121048
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
448 AM CST Mon Jan 12 2026

.KEY MESSAGES...

- Temperatures are expected to warm through Tuesday before a cold frontal
  passage brings readings closer to normal for the remainder of
  the week.

- A stronger cold front is likely to move through Friday night, ushering
  in a (brief) period of well-below normal temperatures for this
  weekend.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 240 AM CST Mon Jan 12 2026

A rapid warmup is in store for today as low-level warm air
advection continues to increase behind the departing surface
anticyclone. Plenty of sunshine is also expected today, and ample
solar radiation combined with southwest winds should yield high
temperatures in the low to mid 50s for much of the area. These
readings would be 15+ degrees above normal for the date.

The pressure gradient weakens this evening, with winds slackening
off. This will be important, especially in river valleys, as winds
decoupling should allow for temperatures to drop fairly rapidly in
the presence of a clear sky. Southwest winds should tick up after
midnight, leading to steady or slowly rising temperatures. Lows
tonight are forecast to be in the low to mid 30s, though some spotty
upper 20s may occur in favored valley terrain across portions of
east central and southeast Missouri.


Gosselin

&&

.LONG TERM...  (Tuesday through Sunday)
Issued at 240 AM CST Mon Jan 12 2026

(Tuesday - Tuesday Night)

Tuesday still looks to be the warmest day of the work week as the
850-hPa thermal ridge moves across the bi-state area. Temperatures
at 850 hPa are forecast to approach +10C, or above the 90th
percentile of climatology. Winds also veer more to the
west/southwest. This is nearly ideal for an unseasonably warm day
across parts of central/east central/southeast Missouri as these
winds downslope off of the Ozark Plateau. The one negating factor is
model RH plots do show a pretty strong signal for increasing
mid/high level cloudiness moving north to south during the day. This
may help prevent temperatures from threatening daily records for the
date (KSTL: 67/1952, KCOU: 66/1952, KUIN: 58/1932). Regardless, it
looks quite warm for climatologically the coldest time of the year.
Highs are expected to range from the mid 50s to mid 60s from south
to north, or 20-25 degrees above normal for the middle of January.

A cold front is forecast to move through the region Tuesday night,
bringing in some colder air into the region. Some light rain showers
also may accompany this front, aided by increasing low/mid level
frontogenesis, ascent downstream of an approaching midlevel
shortwave trough, and enhanced divergence beneath the righ-entrance
region of an upper-level jet streak. Chances of measurable rain on
the latest LREF are in the 20-60% range. Current forecast PoPs are
lower (20-30%), in part due to subtle timing differences of the
front. Therefore, PoPs may increase over the next 24-36 hours.
Regardless, any precipitation looks very light (few hundredths).


(Wednesday - Friday)

Low-level cold air advection will increase substantially during the
day on Wednesday, as 850-hPa temperatures drop well below -10C by 0Z
Thursday. Surface temperatures are likely to drop into the low to
mid 30s, with the warmest part of the day expected in the morning
hours. A few snow showers may also occur during the afternoon hours
along/east of the Mississippi River as a strong midlevel vorticity
maxima moves south of Lake Michigan.

Seasonably cold conditions are expected Wednesday night and Thursday
along with dry weather. Lows Wednesday night are expected to be in
the 10s, or 5-10 degrees below normal. Subfreezing highs are
forecast for a majority of the area on Thursday, with the exception
of parts of central and southeast Missouri where mid 30s are
forecast.

Surface winds quickly turn out of the south Thursday night as the
surface ridge moves off to the southeast. Milder lows are expected
as a result,  generally in the mid to upper 20s. Highs on Friday are
forecast to rebound into the upper 30s to mid 40s ahead of an
approaching arctic cold front.


(Friday Night - Sunday)

The aforementioned arctic cold front is forecast to move through
Friday night. A (brief) period of well-below normal temperatures is
expected behind this boundary, centered on this weekend. This
incoming air mass looks to have its origins from Alaska, which has
been abnormally cold for much of the month of January. Forecast
temperatures in the interior of Alaska are expected to be in the -40
to -50F range early/mid week. Ensemble guidance has gradually
trended colder and colder with this respective air mass across our
region, with the NAEFS now showing 850-hPa temperatures between -15
and -20C, below the 5th percentile of climatology. The deterministic
GFS/ECMWF are even colder, which makes sense given they have a lobe
of the tropospheric polar vortex descending toward the mid-
Mississippi Valley Saturday morning. One major limiting factor is
the lack of snow cover, not only here locally, but also upstream
into Iowa. The latest NOHRSC analysis shows little/no snow cover
until you get into North Dakota and Minnesota. This lack of snow
cover should help the air mass modify more as it heads southward
into the mid-Mississippi Valley. Even given that though, it
certainly looks unseasonably cold. Highs this weekend are forecast
to be below freezing for most locations, with the coldest morning
likely Sunday morning. This is when lows in the single digits to low
teens are forecast. Northwest winds are also likely to be in the 10-
15 mph Sunday morning, so wind chill values below zero are possible.
Probabilities for below zero wind chill values Sunday morning on the
LREF continue to increase, now in the 30-50% range. At this point,
cold weather advisory criteria does not look particularly likely,
with chances for below -10F wind chill values on the LREF in the 10-
3 0% range. However, if colder trends continue, we may get at least
close to advisory criteria for portions of the area so this will
have to be monitored.

In terms of precipitation chances, given the very cold air mass
moving in, anything that does fall should be snow. There also will
be multiple chances for light snow. One will be along/behind the
arctic front itself (Friday night) and another in the cyclonic flow
aloft Saturday. Right now, the better chance appears to be Friday
night along/behind the arctic front. Deterministic guidance shows
some low/mid level frontogenesis. This mesoscale forcing may be just
strong enough to squeeze out some light snow amounts across portions
of the area. LREF probabilities for measurable snow are in the 40-
60% range from southwest to northeast. Light is the key word
however, as chances for at least 1" of snow drop significantly (at
or below 25%).


Gosselin

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 440 AM CST Mon Jan 12 2026

Southwest wind speeds will increase in speed closer to 10 knots
later this morning. A mostly clear sky is expected through the
period, other than a few cirrus. The main concern is for low-level
wind shear overnight tonight. Winds around 2 kft AGL veer more to
the west and increase in speed to near 40 knots. Introduced LLWS
at KCOU/KUIN before midnight and KUIN later on tonight.

Gosselin

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion