809
FXUS63 KLSX 092324
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
524 PM CST Mon Feb 9 2026

.KEY MESSAGES...

- After a brief warm up, a cold front on Tuesday brings a shift
  back toward near normal temperatures for mid February.

- A storm system this weekend brings the first significant rain
  chances (70 to 80 percent) in a while.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 205 PM CST Mon Feb 9 2026

Today`s warm up will be relatively short lived. Although surface
high pressure is shifting eastward through the Great Lakes and
ridging is spreading eastward aloft, already a cold front is
developing across the Northern Plains which will shut off this round
of warming when it arrives tomorrow. We`ll remain quite mild
tonight, in the 40s for most, but the front moves through our
area pretty early in the day on Tuesday. This shifts winds to the
north and initiates cold advection. Although temperatures aloft
(850mb) drop some 15C (almost 30F) behind this front, the impact
at the surface will be muted by the daytime frontal passage and
much deeper mixing behind the front. By comparison, during our
warm up today, we are only mixing about 1,000 feet up, with much
of the more extreme warmth inaccessible further up. Tomorrow
behind the front we`ll be mixing to around 2,500 feet, so despite
much cooler temperatures aloft the deeper mixing still allows for
mild surface temperatures. In fact, southern areas south of
I-44(MO)/I-70(IL) are likely to be a few degrees warmer on Tuesday
than they were today in part due to a cold frontal passage a
little later in the day. Further north and west the temperature
won`t rise much from its mild morning levels, peaking in the 50s.
With this front cutting so far south beneath the ridge and the
forcing with the driving trough remaining well to the north, this
will be a dry frontal passage.

Kimble

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 205 PM CST Mon Feb 9 2026

Although we see a cool down behind Tuesday`s front, we`re still
under the influence of ridging aloft centered over the Southern
Plains. As a result, we never really get that cold behind this front
as temperatures will still be near or slightly above normal in the
heart of this cooler air mass Wednesday through Thursday. While
otherwise dry during this stretch, there will be a weak wave
dropping southeast along the edge of the ridge on Thursday with the
potential to bring some light precipitation to our region. The
forcing here is weak and the moisture return ahead of it is
similarly limited, so this will be pretty unimpactful if it occurs.
There is at least a small possibility that this precipitation falls
as snow, particularly if the wave tracks a bit further east into
Illinois where cold air is deeper. Among the 00Z low resolution
guidance, only 10 to 20 percent of ensemble members produce any snow
across western Illinois, with less than 10 percent producing up too
0.5 inches. Surface temperatures are marginal (near freezing) in an
otherwise mild pattern, so the chances of impacts to roads are even
lower.

The big story of this forecast, though, is the potential for the
first significant rain we`ve had in quite a while. A chance to rinse
the roads of the winter salt and grit and bring a natural car wash.
While ridging maintains its presence across the center of the
country, a southern stream cut off low tracks eastward across the
southern tier of the country Saturday into Sunday. There will be
considerably more Gulf moisture available with this wave, and being
cut off from colder air well to the north it will be a primarily
rain event. Guidance sources do vary on the track of this wave, and
thus where the heavier rain falls. There remains the potential for
this wave to entirely miss our region, though the potential for a
complete miss is low at this point. The operational 12Z GFS remains
a bit of an outlier among the global guidance in tracking this wave
so far south that only our southern fringes see any precipitation.
But even 60 to 90 percent of the 12Z GEFS ensemble members produce
rain (0.01 or more) across our entire region, with those percentages
increasing even more when adding in ECMWF and CMC ensemble members.
Looking at the full 12Z ensemble guidance, 40 to 70 percent of
ensemble members produce at least 0.5 inches of rain across our
forecast area. It`s been a while since most of us have seen that
kind of rainfall. For comparison, the last significant rain (not
snow) at STL was 0.45 inches on December 18, or going further back,
0.53 inches on November 21.

While there is typical uncertainty on the track of this weekend`s
wave, synoptically this type of system would favor rainfall in the
warm advection ahead of the wave, with the uncertainty stemming on
how far north the wave tracks and how well this rainfall focuses
along a warm front. If convection helps to focus the rain along the
warm front, then a more narrow swath of heavier rainfall would be
expected with other areas missing out. A deeper trough, though,
would loop in more moisture around the system and provide a broader
rainfall to the region.

As mentioned before, this being a southern stream wave means that
temperatures would favor this being a primarily rain event. However,
some guidance sources which feature a stronger trough do wrap in
enough cold air for wintry precipitation on the northern and western
fringes. Among those that do, most of this occurs briefly and after
the initial round of rainfall. Among the 12Z ensemble guidance, 10
to 20 percent produce any (0.1 or more) snow from this system
demonstrating why our confidence is fairly high that this will be
primarily rain.

After this wave passes by, guidance is in good agreement that
ridging takes hold again in its wake, leading to warmer temperatures
returning. By Monday, NBM probability of 60+ degrees reaches 40 to
70 percent mainly west of the Mississippi River. That`s about 15
degrees above normal for this time of year.

Kimble

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 522 PM CST Mon Feb 9 2026

Low-level wind shear is the main concern for tonight as winds veer
and increase in speed with height late this evening. Added LLWS at
most terminals given the directional and speed shear within the
lowest 1.2 - 1.5 kft AGL of the atmosphere. LLWS will end from
northwest to southeast as a cold front moves through the region
late tonight into Tuesday morning. Behind the front, look for
surface winds to veer from the south to the north/northwest.

Gosselin

&&

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

$$

WFO LSX