849
FXUS63 KLSX 292330
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
530 PM CST Mon Dec 29 2025

.KEY MESSAGES...

- Temperatures will gradually trend warmer through the upcoming
  weekend, but by how much remains uncertain.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 211 PM CST Mon Dec 29 2025

Winter is back with vengeance, with temperatures currently running
40-50 degrees colder this afternoon than at this point yesterday.
With the axis of the upper-level trough just to our east per water
vapor imagery, northwesterly flow is deep over the Middle
Mississippi Valley and continues to push Arctic air into the region.
Through this evening, winds will continue to gradually weaken as
yesterday`s low pushes further northeastward and the pressure
gradient slackens. The patch of broken stratus currently blanketing
much of the area will also dissipate early this evening.

This clearing stratus and winds weakening further due to surface
ridging building into the area will set the stage for an
increasingly ideal setup for radiational cooling tonight.
Temperatures have been lowered slightly compared to the previous
forecast to account for this, though they still are a degree or two
warmer than last night and will not have as much bite due to the
lighter winds.

The axis of the aforementioned surface ridge will shift eastward on
Tuesday, and the ridge will deamplify as our Arctic post-frontal
airmass wins out, keeping flow through the depth of the atmosphere
over the area northwesterly. However, with the core of the air mass
pivoting eastward with the upper-level trough, low to mid-level
temperatures will recover by several degrees C, correlating with a
nearly 10 degree F jump in surface temperatures compared to today.
Portions of central and southeastern Missouri will see the greatest
boost in temperatures thanks to partly sunny skies. This subtle
warming trend will carry into Tuesday night, with overnight lows
near climatology - mid to upper 20s.

Elmore

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 211 PM CST Mon Dec 29 2025

Both deterministic guidance and ensemble clusters show deep
northwesterly flow over the Midwest at the start of the extended
period on Wednesday morning. Furthermore, guidance consensus is that
this northwesterly flow will persist over the region through the
weekend. The uncertainty in the forecast through this stretch comes
from the degree of northwesterly flow and its impact on
temperatures. More persistent northwesterly flow favors temperatures
running a little below climatological normals - upper 30s to low 40s
for highs, mid 20s for lows - while weaker northwesterly flow would
favor at to just above these normals. Spread within the global
ensemble IQR of temperatures of nearly 10 degrees at times through
this stretch leads to low confidence in specifics. Ensemble means do
support a gradual warming trend toward the weekend as the upper-
level trough over the eastern CONUS weakens, though the 13z NBM (our
forecast) is at the warmer end of the spread. While the spread of
solutions does not support the deterministic forecast favoring one
outcome over another, it also does not support nudging the forecast
toward the middle ground. Notable changes to forecasted temperatures
toward the end of the week may occur in the coming days as guidance
hones in on a common solution.

Within this northwesterly flow, we will need to monitor for embedded
disturbances passing through the region that may lead to
precipitation chances. As of now, there is little to no signal among
deterministic guidance of notable disturbances, and a majority of
global ensemble members are dry through the weekend. The exception
is a minority of members (15% or less) that have very light rainfall
on Friday and Saturday, likely associated with a system forecast to
pass through the Gulf States. Given the low probability of such an
outcome and the majority of solutions showing a pattern locally
unfavorable for precipitation, a dry forecast will be maintained.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 529 PM CST Mon Dec 29 2025

Ceilings are lowering gradually this evening increasingly into
MVFR, but clearing is still expected to advance into the region
from the northwest later this evening with VFR flight conditions
prevailing thereafter. Northwesterly winds will also become
lighter through the night with gusts subsiding. As a surface
pressure ridge passes, winds will back to the southwest on
Tuesday.

Pfahler

&&

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

$$

WFO LSX