041
FXUS63 KLSX 180421
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1021 PM CST Wed Dec 17 2025

.KEY MESSAGES...

- Widespread rain showers are forecast on Thursday associated with
  a cold frontal passage. Gusty (30-40 mph) northwest winds are
  forecast behind the front Thursday late afternoon/evening.

- After a brief return to seasonably cold temperatures on Friday,
  milder weather returns this weekend through the holiday week.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 228 PM CST Wed Dec 17 2025


Broad, weak low-level moisture convergence is expected to begin
this evening in southeast Missouri and move north/northeast with
time. Isolated to widely scattered showers are possible, mainly
before midnight across southeast Missouri and southwest Illinois.
By late tonight into early Thursday morning, the first of two cold
fronts will begin to approach central/northeast Missouri near
daybreak. More widespread rain shower activity is expected along
this frontal boundary, aided by strong surface convergence along
with mid/upper level diffluence. This area of showers should sweep
from west to east with the front. An isolated rumble or two of
thunder is also possible, mainly across southwest Illinois between
1500 and 1800 UTC as the boundary exits the CWA. Rain chances
really drop behind this initial cold front, but a few isolated
showers may be possible along the second of the double-barreled
cold front during the late afternoon across northeast Missouri and
west-central Illinois. Behind this front, some snow showers are
possible in northeast Missouri and west-central Illinois Thursday
evening.

In terms of rainfall totals, most locations are forecast to see
between 0.20-0.40". HREF probabilities for at least 0.25" of rain
range from 30-80% from west to east. Given the limited coverage of
shower activity ahead of the front, limited duration of the more
widespread rain along the initial cold front, and lack of true
convection expected, more substantial rainfall amounts are very
unlikely. The LPMM of the HREF is below 0.50" areawide.

Winds are another concern on Thursday. More specifically, the
strongest winds should be behind the second cold front late
afternoon/early evening on Thursday. Gusts of 35-40+ mph are
expected, especially in northeast Missouri and west-central
Illinois. A brief, isolated gust to 45+ may is possible given almost
50 knots of flow at the top of the mixed layer. However, the signal
is very brief over a very small area. Therefore, did not issue a
wind advisory at this time. HREF probabilities for 45+ mph gusts are
also very small (<20%). These probabilities probably undersell the
potential a little, but nonetheless, do suggest that widespread
advisory level gusts are quite unlikely.


Gosselin

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 228 PM CST Wed Dec 17 2025

(Friday)

A very brief return to seasonably cold temperatures remains on the
table for Friday behind the secondary cold front. After a cold
morning (lows in the upper 10s/low 20s), highs in the mid 30s to low
40s are expected from northeast to southwest. These readings would
be almost 5 degrees below normal for the date.


(Friday Night - Sunday Night)

A quick moderation is forecast heading into the weekend as low-level
warm air advection increases ahead of another approaching cold
front. Saturday definitely looks to be the "pick" day of the weekend
with dry conditions and highs in the 50s. A cold font should sweep
through the region Saturday night, bringing in a return to slightly
below normal temperatures. Lows Sunday morning are forecast to be in
the 20s, with highs on Sunday in the 40s.


(Monday - Next Wednesday)

A more pronounced warming trend looks to commence leading up to the
Christmas holiday. Very anomalous (500-hPa heights near 99th
percentile) mid/upper level ridging is being shown on both the
EPS/GEFS mean, with not a whole lot of variability in the strength.
This leads to high confidence in this pattern, which should yield
warm and dry conditions across the central CONUS. High temperatures
are most likely to reach the mid 50s to low 60s each of Tuesday and
next Wednesday. Lows should also be on the mild side and above the
freezing mark. Even the 25th percentile of the NBM for highs/lows
during this period are around 10 degrees above normal, further
illustrating the high degree of confidence in the magnitude of this
upcoming warm weather pattern.


Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1021 PM CST Wed Dec 17 2025

Strengthening southerly winds will continue overnight with ceilings
also lowering to MVFR. IFR ceilings are also possible, but current
indications are that they will be most prevalent across southeastern
MO and southwestern IL. On Thursday morning into midday, a cold
front will pass from west to east, accompanied by increasing showers
and winds veering to westerly. These showers could produce a brief
period of IFR flight conditions and stronger wind gusts at KUIN and
St. Louis metro terminals but are expected to only last less than an
hour. Behind the front, VFR flight conditions will return as
ceilings scatter during the afternoon. A secondary cold front will
traverse the area Thursday evening with winds veering to
northwesterly and wind gusts increasing to 30 to 35 kt.

Pfahler

&&

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

$$

WFO LSX