Severe Thunderstorm Warning 186, NWS St. Louis, MO

Area Forecast Discussion
National Weather Service Saint Louis MO
207 PM CDT Wed Jun 17 2026

.KEY MESSAGES...

- Severe thunderstorms move southeast across the region this
  evening, ending during the early overnight hours.

- Tonight's cold front brings cooler and drier conditions for the
  rest of the week. Rain chances return this weekend.

&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 206 PM CDT Wed Jun 17 2026

Strong southwest flow has brought in a warm, humid air mass just
ahead of an advancing cold front. This is leading to a rapidly
destabilizing environment this afternoon with thunderstorms expected
ahead of the front. Unusually strong wind shear will lead to strong
potential for storms to organize into supercells capable of large
hail, damaging winds, and tornadoes. Very high precipitable water
values near 2 inches suggest very heavy rainfall rates are likely,
though quick storm motions should minimize the duration in any one
location. Low level wind flow out of the southwest ahead of the
front minimizes the effective convergence along it, so storm
coverage may be initially isolated. In addition, shear vectors
oriented across the boundary suggest storms should remain more
discreet with less potential for a more organized cold pool driven
MCS. A locally greater tornado threat may exist in the vicinity of
the remnant outflow boundary laid down by this morning's storms
across Illinois. Near this boundary convergence will be stronger
along with the potential for locally greater low level wind shear.
Storm coverage is expected to decrease after sunset with the front
bringing in a drier and cooler air mass behind it.

Guidance consensus is that the front settles just south of our area
on Thursday, with lingering showers or thunderstorms similarly
staying just to our south. However, some of these could drift into
the southern periphery of our forecast area. Otherwise, additional
very light, low topped showers may develop behind the cold front as
low level lapse rates maximize tomorrow afternoon. However, an
inversion aloft will limit the depth of these showers, so the impact
will be quite minor from just a few sprinkles. Otherwise maximum
temperatures will be about 10F cooler on Thursday compared to today,
with dewpoints similarly lower by about 10F.

Kimble

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 206 PM CDT Wed Jun 17 2026

The trough driving today's action digs out a rather broad low
amplitude trough over the eastern US for the rest of the week, with
similarly low amplitude ridging over the western US. This puts us in
northwesterly flow which favors subsidence aloft and surface high
pressure, although a few weak cold fronts can also occur. So our
forecast for the next several days favors cooler and drier
conditions.

As ridging gradually pushes east toward the Rocky Mountains,
moisture return begins across the Plains later this week. By
Saturday a shortwave trough rounding the top of the ridge triggers a
round of showers and storms in Nebraska and Kansas, the remnants of
which push ESE toward our area Saturday night. This represents our
next best chance of rain. Models vary on how the shortwave trough
and associated features progress, in part due to the convection
associated with it. If this shortwave is a bit slower and the
moisture return makes it northward into our area then we could
develop a local severe weather threat on Sunday. However, confidence
remains low on this due to variance in the guidance on the track and
timing of this wave. Either way, this Saturday night into Sunday
period represents our best chance of rain locally within this 7-day
forecast. Among the long range ensemble guidance, up to 40 percent
of members bring precipitable water values up above 2 inches, so a
locally heavy rain threat will exist. A flash flood threat could
materialize if mesoscale features can align to produce training or
prolonged thunderstorm activity. After Sunday's wave trends favor
drier and mild conditions again under renewed northwest flow.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1218 PM CDT Wed Jun 17 2026

Strong southwest winds are expected today with gusts occasionally
near 40KT in spots. Thunderstorms are expected to initiate early
this afternoon in northern Missouri, tracking southeast ahead of a
cold front. These storms could be locally severe. Winds shift to
the WNW and slacken behind the front this evening.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory until 8 PM CDT this evening for Franklin MO-
     Gasconade MO-Jefferson MO-Lincoln MO-Madison MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Warren MO.

     Wind Advisory until 6 PM CDT this evening for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Knox MO-Lewis MO-Marion MO-Moniteau
     MO-Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Shelby
     MO.

IL...Wind Advisory until 8 PM CDT this evening for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Randolph IL-
     Saint Clair IL-Washington IL.

     Wind Advisory until 6 PM CDT this evening for Adams IL-Brown IL-
     Pike IL.

&&

WFO LSX