Area Forecast Discussion

173
FXUS63 KLSX 191151
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
551 AM CST Mon Jan 19 2026

.KEY MESSAGES...

- Another Arctic airmass is moving into the region today.
  Dangerous wind chill readings as low as -15 are expected through
  mid-morning and a Cold Weather Advisory remains in effect until
  1000 AM.

- The weather will remain dry at least through Thursday, and
  temperatures will warm to near or just above seasonal normals.

- There is a chance that another Arctic airmass will move into the
  Midwest Friday into Saturday. The details of the forecast remain
  uncertain, but there is a chance for snow and bitterly cold
  temperatures.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 409 AM CST Mon Jan 19 2026

Another Arctic airmass will move south from the Northern Plains
today, to settle into the Lower Mississippi Valley tonight.  Strong
northwest flow over the area this morning is combining with very
cold temperatures to produce wind chill values as low as -10 to -15
across northeast Missouri into south central Illinois.  Therefore
the Cold Weather Advisory looks to be in good shape and no changes
in area or timing are anticipated at this time.  The cold start to
the morning along with persistent cold advection will keep afternoon
highs well below normal in the upper teens to low 20s in most
locations.  Winds become light and variable tonight as the Arctic
high drifts into the lower Mississippi Valley.  Forecast soundings
suggest the evening will be mostly clear which will produce good
radiational cooling conditions, however guidance shows a slug of
moisture between 850-700mb moving over the forecast area after 06Z.
This would hamper the cooling after midnight, and the wind will be
turning to the south as well.  This implies a quick cool down with
the radiational cooling during the evening and then steady or slowly
rising temperatures overnight.  It`ll still be cold Tuesday morning
with temperatures in the low to mid teens around 12Z.  Luckily the
wind is forecast to be at or below 5kts so another Cold Weather
Advisory will not be necessary.  Temperatures moderate on Tuesday
with warm advection and increasing south-southwest flow.  Current
indications are that there will be decent insolation as well with a
partly to mostly sunny sky in most locations.  Guidance is in good
agreement that most of if not the entire area will see temperatures
above freezing in the mid 30s to low 40s with the possible exception
of far northeast Missouri into west central/south central Illinois
where afternoon clouds develop ahead of the next short wave.


Carney

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 409 AM CST Mon Jan 19 2026

The weather pattern for Wednesday through at least Friday will be
characterized by deep cyclonic flow around an upper low over the
Hudson Bay.  Deterministic guidance is in good agreement in pushing
a short wave through the Mississippi Valley on Wednesday. Warm
advection ahead of the wave produces the warmest day of the week
with highs ranging from around 40 in west central Illinois to 50 in
southeast Missouri. Minor timing differences with respect to the
front yield some uncertainty in these temperatures with ensemble
high temperature IQRs of 4-6 degrees.  Models show the core of the
upper level low digging down to near the U.S./Canada border by late
Thursday which allows colder air to intrude into the Midwest, and
The GFS and ECMWF both show another wave digging into the Plains on
Friday. This wave drags a 1045+mb surface high with bitterly cold
air into the Midwest and the center of the high settles over
northeast Iowa/southwest Wisconsin Saturday morning.  LREF cluster
analysis shows a relatively high degree of variance in the depth of
wave which moves this strong high pressure system into the Midwest.
This has downstream effects on the position and strength of the high
and resulting temperatures for our area.  However, there`s a chance
we`ll see the coldest temperatures of the season so far with the NBM
showing Saturday morning lows ranging from around -5 in northeast
Missouri and west central Illinois to around 0 along the I-70
corridor to about 5 above in southeast Missouri.  Along with the
cold air some medium range guidance members are showing a chance for
snow Friday through Saturday night.  However confidence that
anything will fall is low at this time due to the aforementioned
variability in the guidance.


Carney

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 542 AM CST Mon Jan 19 2026

VFR flight conditions are expected to prevail through the period.
There are a few snow showers with bases around 3000 ft AGL moving
southeast from east central Missouri into southwest Illinois. The
showers should affect any given point for only a few minutes
before moving off. Gusty northwest flow will weaken this afternoon
and turn to the south late tonight as high pressure moves from the
Plains into the Lower Mississippi Valley.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory until 10 AM CST this morning for Knox MO-
     Lewis MO-Marion MO.

IL...Cold Weather Advisory until 10 AM CST this morning for Adams IL-
     Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Montgomery IL-
     Pike IL.

&&

$$

WFO LSX

NWS LSX Office Area Forecast Discussion