Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

635
FXUS63 KLSX 180340
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1040 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 06z TAFs through 06z Thursday Night)
Issued at 1038 PM CDT Wed Jun 17 2026

Scattered showers and weak thunderstorms may impact metro
terminals over the next few hours ahead of a cold front. These
storms will push off to the southeast after midnight into
southeast Missouri/southwest Illinois. Dry/VFR weather is favored
thereafter, though some shower activity may threaten the terminals
along a secondary front on Thursday. Winds are expected to be out
of the northwest for the most part behind tonight`s cold front
through the period.

Gosselin

&&

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

$$

WFO LSX