827
FXUS63 KLSX 042008
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
208 PM CST Tue Nov 4 2025

.KEY MESSAGES...

- Above normal temperatures are expected to continue through
Saturday.

- A strong cold front is expected to move through the area Saturday
night which will lower temperatures 20-25 degrees for Sunday and
Monday.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 207 PM CST Tue Nov 4 2025

A short wave trough currently over southwest Canada will dive
into the Midwest tonight into Wednesday morning. The surface
reflection of the trough will move almost due east across the
Great Lakes region and drag a cold front through the Mid
Mississippi Valley Wednesday. The front isn`t expected to move
into northeast Missouri until around 12Z Wednesday morning, and
the southwest flow ahead of it will keep Wednesday morning`s lows
in the 50s, around 10-15 degrees warmer than this morning. The
warmer start to the day will contribute to mild afternoon highs
again on Wednesday despite the passage of the cold front. Forecast
soundings show little if any potential for clouds, let alone
precip, and strong insolation due to lack of clouds will only help
temperatures to rebound from morning lows. However there is some
disagreement on the strength of cold air advection behind the
front on Wednesday afternoon. Traditional MOS (MAV/MET) shows a
difference in highs of as much as 9 degrees. LREF and NBM IQRs are
closer, but are still 3-5 degrees, primarily in the vicinity of
the I-70 corridor. With that in mind, I leaned a bit toward the
higher end of guidance with highs ranging from the low 60s in
northeast Missouri to around 70 in southeast Missouri and
southwest Illinois due to the aforementioned warm start to the day
and lack of clouds. The real impact of the cold front will be
lower surface dew point temperatures. This combined with light
winds and a clear sky Wednesday night will produce excellent
radiational cooling conditions allowing temperatures to fall into
the mid to upper 30s across most of the area.

Carney

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 207 PM CST Tue Nov 4 2025

The wave train continues with at least 2 more before the end of the
period. The first is forecast to move across the Rockies into the
Great Plains late Thursday night.  Southerly flow ahead of the wave
will help to produce a 25-30 degree warm up from morning lows on
Thursday with highs topping out in the low to mid 60s. This trough
is deeper than the one moving across the Midwest Wednesday, and it
taps into a little Gulf moisture.  A southwesterly low level jet
increases to around 40kts Thursday evening, producing weak to
moderate moisture convergence over the Mid Mississippi Valley mainly
late Thursday night into Friday.  Most guidance members spit out
some QPF during this period, and there`s even some instability in
the warm sector.  The NBM probability of thunder on Friday ahead of
the cold front is ~20%. This looks reasonable with around 400 J/Kg
MLCAPE.  0-6km shear is forecast to be around 50kts, but with the
limited instability storms should remain below severe thresholds.
This may change though if more instability develops than expected.

The second wave follows quickly on the heels of the first this
weekend.  It moves across the Plains Saturday and phases into the
long wave pattern to produce a very deep trough stretching from the
Hudson Bay through the Great Lakes all the way to the Gulf Coast by
00Z Monday.  This pulls an Arctic airmass into the middle of the
country and our temperatures plummet.  Latest guidance keeps most of
the precip associated with this system north of our forecast area
across Iowa and northern/central Illinois.  However there could be a
little light rain Saturday night and Sunday, and perhaps some snow
flurries Sunday if enough moisture can hang back in the cold air.
Highs will fall from mid 60s to around 70 Saturday down to the low
to mid 40s on Sunday and Monday.  The entire area should experience
a hard freeze both Sunday and Monday with lows in the low to mid
20s. Current thinking is that temperatures will moderate on Tuesday
as the high moves into the southeastern U.S. and south-southwest
flow returns to the Mid Mississippi Valley.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1133 AM CST Tue Nov 4 2025

VFR flight conditions are expected to prevail through the period.
Expect low level wind shear to develop this evening as a 40-50kt
low level jet overspread the region ahead of a cold front which
will move through Wednesday morning. Gusty south to southwest flow
this afternoon will diminish this evening and then turn to the
northwest Wednesday morning as the cold font passes.

Carney

&&

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

$$

WFO LSX