608
FXUS63 KLSX 121833
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
133 PM CDT Tue May 12 2026

.KEY MESSAGES...

- The temperature peaks in the 80s today ahead of a cold front.
  Scattered showers and an isolated thunderstorm are possible as
  the front moves through this evening. The severe weather threat
  is low.

- After a brief cool down behind the front, even warmer weather
  arrives by this weekend.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 123 PM CDT Tue May 12 2026

Water vapor imagery reveals a shortwave diving out of south-central
Canada into the Upper Great Lakes. In response, a surface low has
moved into northern Wisconsin, with a cold front trailing to the
southwest through Iowa and into Kansas. These features will
continue to drift to the east/southeast, pushing the cold front
into the Mid-Mississippi Valley this evening. Gusty winds ahead of
the front, coupled with the recently tilled soils, do raise some
concerns about blowing dust. Fortunately today`s winds/antecedent
conditions are noticeably lower/less conducive than in previous
blowing dust events, so the potential for impactful blowing dust
appears to be quite low (<15%).

As the front moves through the area this evening and tonight, there
is a low chance (<30%) that it provides enough lift to squeeze out a
few showers over our area. However, the combination of poor moisture
return and low level warm air advection ahead of the front will
significantly limit and cap instability. Therefore thunderstorm
chances are very low (<15%).

BSH

&&

.LONG TERM...  (Wednesday through Next Tuesday)
Issued at 123 PM CDT Tue May 12 2026

Deep north-northwesterly flow behind the front and parent shortwave
will persist through the day on Wednesday before upper level ridging
and southerly low level flow take hold on Thursday. This will push
tomorrow`s temperatures 5-10 degrees cooler than today, warming just
a bit on Thursday as southerly winds increase.

The upper level pattern will become more zonal by the end of the
workweek, gradually becoming southwesterly toward the end of the
weekend as a deep trough moves over the western CONUS. This will
result in persistent southwesterly low level flow over the Mid
Mississippi Valley through the weekend, which will in turn advect
warmer temperatures and deeper moisture into the region. The
return of deeper moisture will keep at least modest instability
over the region through the period.

I expect to see at least a few impulses ripple through the
zonal/southwesterly upper level flow from the end of the workweek
through the weekend, which coupled with the lingering instability,
should result in some showers and thunderstorms. Unfortunately, it
is difficult to confidently pin down the details of these
impulses and resultant storm chances, so our forecast currently
features persistent, low precip chances all weekend. I expect
there will actually be plenty of dry time this weekend, and we
should be able to focus this forecast as we get closer to the
weekend.

As far as temperatures are concerned, the NBM remains stuck on the
very high end of forecast guidance and appears unlikely to be
correct. Even if we assume the 90th percentile of 850mb temperatures
from the GEFS/ENS/GEPS and full mixing to the surface, I still only
expect highs in the low 90s. There is no strong evidence to
support that we`ll be near the 90th percentile, and full mixing
appears unlikely given the above rain/cloud chances through the
weekend.

The upper trough will push toward the central CONUS early next week
and will lead to more focused shower and thunderstorm potential. The
trough will also lead to greater deep layer shear than what we`re
expecting this weekend, so this will represent the best chance for
severe storms over the next week. However the details remain murky
at this forecast range, leading to low forecast confidence at this
time.

BSH

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1205 PM CDT Tue May 12 2026

Gusty southwest winds will persist through the afternoon before
tailing off around sunset. A cold front will then sweep through
the region this evening and overnight, turning winds to the
northwest. There is a low chance (<20% at all terminals) that the
front will fire a few showers as it passes, but given that level
of confidence, I`ve left any mention of precipitation out of the
TAFs.

BSH

&&

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

$$

WFO LSX