Area Forecast Discussion

818
FXUS63 KLSX 200448
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1048 PM CST Mon Jan 19 2026

.KEY MESSAGES...

- Another round of bitterly cold Arctic air is expected this upcoming
  weekend.

- The cold air this weekend will bring the threat of snowfall to
  the area, though confidence in this occurring is low.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 250 PM CST Mon Jan 19 2026

The large scale upper-level pattern is currently being driven by a
robust trough over Ontario with a weakening ridge to the west over
the Pacific coast, placing us under northwesterly flow aloft.
Current surface analysis shows a departing low pressure system over
the Great Lakes region, the same system that brought last night`s
FROPA and reinforcing shot of Arctic air, along with an Arctic high
pressure over Kansas. This pressure setup has led to strong and
gusty northwesterly surface winds that have resulted in a very slow
warmup despite an abundance of solar insolation today. Afternoon
high temperatures across the region will peak in the upper 20s to
the south with only mid teens to the north.

The Arctic high to the west will slowly slide to the southeast
tonight over southern Missouri. As this happens, surface winds will
weaken around sunset with river valleys and other low-lying areas
likely going calm and variable, especially over the Ozarks which
will be closer to the high pressure center. This will allow for
efficient radiational cooling right after sunset leading to a quick
initial drop in temperatures. By early morning, the Arctic high will
be over Tennessee placing us under southerly surface flow. This,
coupled with an area of mid-level clouds moving in from the
northwest after midnight, will slow the cooling with temperatures
expected to hold steady or even moderate slightly before sunrise.

With southerly surface winds (5-10kts) and a mostly sunny sky
tomorrow, a quick warmup will be in store with the entire area
forecasted to get above freezing for highs tomorrow afternoon. The
wind direction favors downsloping off the Ozark Plateau which will
aid the fast warmup with some low 40s possible in central and
southeast Missouri. The robust upper-level trough to our northeast
begins to broaden tomorrow, which allows an embedded shortwave to
swing southeast towards the area. By Tuesday afternoon, this upper-
level shortwave will be over the Northern Plains, while its surface
reflection begins to form on the leeward side of the Rocky Mountains
leading to increased southwesterly flow over the Mississippi River
Valley Tuesday night. This, along with increasing cloud cover, will
keep temperatures relatively mild Tuesday night into Wednesday
morning with lows in the upper 20s to low 30s expected ahead of this
systems approaching cold front.

Peine/Elmore

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 250 PM CST Mon Jan 19 2026

At the start of the extended forecast period Wednesday morning,
guidance consensus is that the aforementioned shortwave will be
pushing into the Great Lakes along with its surface reflection. The
attendant cold front will be somewhere generally across the CWA, and
while low-level moisture continues to look meager with this FROPA,
ensemble-based probabilities have around a 25% chance for measurable
precipitation from roughly Reynolds County, MO northeastward through
Marion County, IL, with chances dwindling rapidly through the late
morning. Upper-level flow is expected to remain quasi-zonal in the
wake of the front, with low-level flow subtly out of the west,
leading to weak cold air advection. Temperatures on Wednesday
actually are forecast to be warmer than Tuesday among a majority
of guidance, showing that this cold front is more Pacific in
nature than a true cold front.

This relative warmth will be short lived, as guidance consensus is
that another front will drop southward through the area Wednesday
night, and this front will be packing colder air. While the general
phasing of the trough will remain steady through this portion of the
period, low to mid-level flow will become increasingly
northwesterly, allow for an Arctic air mass to intrude much of the
Midwest. This air mass will only become further entrenched over the
region through Saturday. Precisely how quickly temperatures drop
through this stretch and how low they become is uncertain due to
differences in the phasing of the upper-level trough among
deterministic solutions and ensemble clusters. However, there is
high confidence that late Friday into Saturday will be the
coldest stretch of the period, with guidance consensus supporting
overnight lows around 0 degrees and highs failing to break out of
the teens for most locations on Saturday. How long this cold
lingers is highly uncertain as we enter the late weekend and next
week, with guidance shifting the heart of the air mass eastward at
different speeds. Slower solutions support a continuation of this
degree of cold, while faster solutions support temperatures
moderating to around seasonal normals early next week. The current
NBM and our forecast is at the 75th percentile for temperatures
through this stretch, and while this seems slightly too
optimistic, it is still within the envelope of statistically
reasonable outcomes.

There is a signal for snowfall among the global ensemble members
starting as early as Friday, though peaking on Saturday. This
snowfall will materialize via one or two mechanisms: subtle forcing
via shortwaves aloft, and/or overrunning moisture from a system
moving through the Gulf States and Southeast. While details on
either driver are fuzzy at this lead time, 70% of guidance has
snowfall occurring across the CWA, with a majority of these
sources having 2" of accumulation or less. However, this is
assuming a 10:1 snow-to-liquid ratio (SLR) which would be much too
low for the degree of cold air in place, with confidence high in
SLR being a little greater than area climatology (12:1).
Therefore, there is a low chance for locally higher totals,
especially if snowfall is driven by shortwaves and resulting
mesoscale banding. While the amount of guidance that shows snow
across the CWA is high, confidence in snowfall actually occurring
remains low to medium. Spread among guidance and run-to-run
variability remains high, and when lead time is factored in,
inherent confidence in impacts at this time is low. Therefore, the
NBM PoPs (around 30%) seem appropriate.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1043 PM CST Mon Jan 19 2026

VFR conditions are expected throughout the 06Z TAF cycle. Light
south-southwest winds will persist through the night and into the
day tomorrow, but will steadily increase tomorrow evening and veer
slightly more to the southwest. Some marginal low level wind shear
will be possible during this period due to very strong winds just
above the surface, but this depends largely on whether a low level
inversion can develop before these stronger winds aloft arrive.
For now, confidence remains too low to include this in the TAF at
this time.

Otherwise, some mid level clouds will move through most terminals
overnight tonight, but ceilings are expected to remain above VFR
levels.

BRC

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion