Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

714
FXUS63 KLSX 211119
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
619 AM CDT Mon Sep 21 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms will come to an end later
  this morning.

- Seasonably cool temperatures are expected for the rest of the
  week.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 327 AM CDT Mon Sep 21 2026

A cold front has been moving through the area since yesterday
and is now through to southeastern MO. There remains some
showers and thunderstorms behind the front in the area, but they
are moving east and out of the area. Some remnant showers may
remain through the day today. These will be tied to the elevated
front at the 850mb level and will move south as the surface
front continues its trek. In the afternoon there could be some
additional convective initiation along the elevated front in
southeastern MO. These showers and thunderstorms are not
expected to pose a threat, as the conditions for strong to
severe thunderstorms are not very favorable with HREF indicating
around 1500 kg/J of SBCAPE and less than 10 kts of shear. There
is also weak low-level cold air advection that would limit
overall development of any convection.

Thanks to the cold front, the end of the relentless heat is
finally here. Temperatures today will be much cooler compared to
last week with high temperatures expected to be in the 60s and
70s, with some locations in the low 80s towards southeast MO.
Today temperatures will be mainly driven by the presence of
widespread low-level clouds, except for southeastern MO where
there will be a lack of cloud cover, and the previously
mentioned weak low-level cold air advection. For areas under the
cloud cover, conditional climatology indicates that when
ceilings are below 2 kft AGL with northerly surface winds, which
is expected today, temperatures are predicted to only rise about
5 degrees from their overnight low temperature. This is what is
expected to occur. Ensemble guidance has become more confident
in the high temperatures in recent runs with interquartile
ranges of only about 5 degrees, compared to yesterday they were
7-10 degrees. Low temperatures are expected to be upper 50s and
low 60s. NBM guidance shows that Tuesdays temperatures will be
similar to Monday, but southeastern MO will be joining the rest
of the party with highs in the mid 70s starting on Tuesday; a
much needed relief from the heat.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 327 AM CDT Mon Sep 21 2026

Seasonably cool temperatures are expected for the rest of the
week. Tuesday night lows across the region are expected to be in
the low to mid 50s. However, the NBM indicates there is a
30-50% chance that our northern area could drop in the upper
40s. This is possible by having an anomalously high surface
ridge of 1036mb (>99% climatological percentile) over the
eastern Great Lakes and southeastern Canada. Models are
confident that this air mass will continue to dominate for the
rest of the week with a gradual warming through the 70s,
reaching the low 80s by next weekend. NBM and LREF guidance has
interquartile ranges of around 5 degrees for each day this week
and into the weekend.

The GFS and EPS ensembles both show an upper and mid-level ridge
building over the southeastern Canada region with a center of
low pressure over the Ohio Valley on Wednesday. The ridge should
remain fairly stationary over southeastern Canada, while the low
pressure center will slowly move to the east coast of the CONUS.
This pattern will allow for continued westerly and northwesterly
flow aloft and northerly winds at the surface to help moderate
our temperatures into next weekend and limit the moisture
transported into the region. This will prevent another return of
the heat and humidity in the foreseeable future; also limiting
the chances for further rainfall during the coming week.

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 618 AM CDT Mon Sep 21 2026

IFR ceilings are starting off the TAF period at all terminals
giving way to MVFR ceilings this afternoon. There is a chance
that there could be some isolated showers or drizzle during the
TAF period, but confidence of impact on visibility is low. There
is also a low possibility of MVFR fog this morning.

&&

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

&&

$$

SHORT TERM...Asel/Gosselin
LONG TERM...Asel/Gosselin
AVIATION...Asel/Gosselin