Area Forecast Discussion

806
FXUS63 KLSX 050504
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1104 PM CST Sun Jan 4 2026

.UPDATE...
Issued at 516 PM CST Sun Jan 4 2026

Clouds are rapidly clearing this evening and we expect once they
do the temperature will drop pretty quickly, especially in
geographically favored cool spots. Similar to last night when
patches of cirrus were not enough to prevent quicker than expected
cooling, we will likely drop into the low to mid 20s in the cold
spots tonight. There is some moist advection that begins by
morning mainly across the western and northern part of our
forecast area. This will likely bring in some low stratus by
morning, but also potentially some fog. As such we`ve added a
mention of fog to the forecast around daybreak Monday.

Kimble

&&

.KEY MESSAGES...

- Dry and mild weather is expected for Monday through Wednesday
  with highs up to around 25 degrees above normal.

- Rain is still expected Thursday and Friday. Confidence remains
  low in the timing and amount of rain that falls.


&&

.SHORT TERM... (Through Wednesday)
Issued at 241 PM CST Sun Jan 4 2026

The forecast for Monday through Wednesday continues to look dry and
warm. Surface winds have already turned to the south across our
area as high pressure drifts east across the Great Lakes Region.
Southerly flow will persist through tomorrow, and a broad upper
level ridge will build overhead. The warm advection will produce
Monday morning lows around 10 degrees warmer than this morning`s
lows, and highs are expected to be 10 to 15 degrees warmer in the
mid 50s to low 60s.

The upper pattern attenuates and becomes more zonal Tuesday and
Wednesday as a weak short wave moves across the Central U.S.  The
surface reflection of the wave moves across the Midwest into the
Great Lakes Region Tuesday.  Low level flow turns to the west on
Wednesday behind the "cold" front on Tuesday, models do not show
much in the way of cold advection.  While drier air will move into
the region behind the front on Tuesday it will remain mild during
the day.  The drier air and light wind will produce better
radiational cooling Tuesday night so lows will be between 5-10
cooler Wednesday morning.  Southerly flow and warm advection returns
Wednesday bringing temperatures back up into the upper 50s to mid
60s.

Carney

&&

.LONG TERM... (Thursday through Next Sunday)
Issued at 241 PM CST Sun Jan 4 2026

There`s still a great deal of uncertainty in the forecast beyond
Wednesday.  The pattern begins reamplifiying Wednesday night as an
upper-level short wave moves ashore over the Pacific northwest and
phases with a closed low spinning off the California coast. Global
deterministic guidance shows the combined trough moving across the
Rockies and into the Great Plains by 12Z Friday.  GFS and ECMWF
continue to differ on how the two waves integrate which causes
differences in amplitude and speed of the overall trough.  This in
turn affects the strength and position of the surface low as it
develops Thursday night into Friday.  Over the past 3 days, the GFS
has shown the Friday 12Z position of the surface low as far
northeast as Madison Wisconsin, and as far to the southwest as Fort
Smith Arkansas.  The ECMWF has had similar run-to-run consistency
issues.  The position and strength of the low will of course have
huge impacts on sensible weather, particularly on Friday as the
system rolls through the Central U.S. Both the NBM and LREF are
showing wide temperature and rainfall IQRs on Friday, as much as 15
degrees and 0.70 inch respectively.  A more northerly solution would
also increase the probability for thunderstorms and possibly severe
weather.  Both the NBM and LREF are showing between 100-200 J/Kg
mean CAPE Friday afternoon.  However, the 90th percentile
(reasonable worst case) shows 500+ J/Kg CAPE which is more than
enough for cool-season severe weather.

The weather turns significantly colder behind the system Saturday
and Sunday.  The LREF mean high temperatures fall as much as 20
degrees by Sunday. However, the LREF also shows a high degree of
variability in the speed and amplitude of the trough as it continues
east through the weekend.  This will ultimately affect how strong
the cold advection behind the system will be, and how long it will
last. With that in mind, temperature IQRs are 5 to 8 degrees leading
to a low confidence forecast.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1050 PM CST Sun Jan 4 2026

Confidence is high in dry and VFR flight conditions through the
forecast period at all local terminals. There is a low chance for
low stratus and fog at KCOU, KJEF, and KUIN around sunrise as a
weak front moves through the area. The better signal for this
threat is just west-northwest of these terminals, so impacts have
been left out of the TAFs for now. A low-level jet nosing north of
the region will produce a narrow window for a marginal threat of
low-level wind shear at KCOU, KJEF, and KUIN at the start of the
period, but confidence is very low in impacts.

Elmore

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion