596
FXUS63 KLSX 311133
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
533 AM CST Wed Dec 31 2025

.KEY MESSAGES...

- There`s a 20% chance for sprinkles and flurries across northeast
Missouri and west-central Illinois this evening.

- Near normal temperatures will continue into the weekend before
warming for the work week, though confidence is low in how much
warming occurs.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 246 AM CST Wed Dec 31 2025

As of 2AM there is a surface low over the Great Lakes region,
associated with a mid-level low near the Hudson Bay region. A
surface trough is pushing through the forecast area this morning,
causing winds to shift to the northeast. The attendant cold front
will drop through the region tonight into Thursday, associated
with an axis of the mid-level low. The lift along the front will
weaken as it drops into Missouri and central Illinois, keeping our
forecast area largely dry. The exception will be across northeast
Missouri and west-central Illinois where guidance is hinting at
just enough lift in the saturated low-levels along the front to
produce sprinkles/flurries tomorrow evening. Sprinkles are
expected to transition quickly over to flurries as the low-level
cool quickly with the front. Confidence is low in more
significant precipitation, there`s only about a 10% chance via the
HREF of 0.01" of QPF along the front in this area.

The surface front will exit the CWA by Thursday morning. 925mb low-
level cold air advection across the northern CWA, combined with
lingering clouds and northerly surface flow will result in cooler
temperatures north of I-70. Highs on New Year`s Day in this area
will be in the low 30s, while relatively warmer low-level
temperatures will result in high temperatures in the upper 30s to
40s south of I-70.

Delia

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 246 AM CST Wed Dec 31 2025

For the past several days the region has been caught in
northwesterly mid-level flow, stuck between a mid-level low across
southeastern Canada, and a mid-level ridge across the Rockies. By
Friday a brief split stream pattern develops out of the mid-level
ridge, the southern stream ridge weakening and allowing a couple
shortwaves to pass eastward into the lower-Mississippi Valley. The
stronger one moves through overnight into Saturday, its surface
reflection moving through Arkansas Friday evening. This system is
still expected to stay to our south, with LREF guidance indicating
only a 20% chance for measurable rainfall across our southern
forecast area. Even this seems a little bullish considering the
mid- Mississippi Valley will be cut off from significant Gulf
moisture. A northern shift in the system could increase rain
chances, however the lack of moisture ahead of the system would
severely limit precipitation coverage and amounts.

In the wake of the shortwave on Sunday, the southern stream ridge
restrengthens to join the northern stream, and the ridge begins to
advance eastward. This is where guidance diverges in the mid-level
pattern, differences exist in how strong the ridge is when it shifts
into the Mississippi Valley over the weekend and whether a shortwave
will weaken the ridge. Differences in the evolution of this feature
continue into the mid-week period. In the absence of significant
moisture return, confidence is increasing in a largely dry forecast
through Wednesday despite the uncertainty in the mid-level pattern.


There is a stronger signal for warm air advection Sunday through the
mid-week period, increasing confidence that temperatures will
continue to warm. How much they warm remains uncertain and tied in
part to the uncertainty in the mid-level pattern. This is reflected
in the 10+ degree interquartile spread for high temperatures during
this period, though the warming trend is evident.
Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 519 AM CST Wed Dec 31 2025

MVFR stratus is moving south into the terminals this morning and
will linger into the late morning before lifting and moving east
out of the terminals. KCOU and KJEF will be the first to clear,
followed by KUIN and the St. Louis metro terminals. VFR flight
conditions will then prevail ahead of a cold front that will drop
south through the area this evening. There is a 40-50% chance that
MVFR ceilings will return to the terminals along the front, but
confidence is not high enough at this point to include a mention
in the TAFs.

Westerly winds around 10 kts will become northerly behind the cold
front tonight, before becoming northeasterly by the end of the TAF
period.

Delia

&&

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

$$

WFO LSX