Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

740
FXUS63 KLSX 212341
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
641 PM CDT Mon Sep 21 2026

.KEY MESSAGES...

- Scattered showers and an isolated sub-severe thunderstorm are
  possible (20-30%) across southern MO/IL this afternoon and
  evening.

- Cool conditions are expected this week with a gradual warmup
  to near normal temperatures by the weekend.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 246 PM CDT Mon Sep 21 2026

Recent GOES-19 visible satellite imagery reveals a broad and
widespread field of low status enveloping a majority of the Midwest
this afternoon. This impressively expansive cloud field is being
driven by northeasterly low-level CAA from the surface to 850mb
across the region. Nearly all of our area has been under the
influence of these lower ceilings today, aside from portions of
southeast MO/southern IL, where the 850mb cold front is located.
Locations where stratus and pockets of mist have prevailed today,
allowing for little to no solar insolation, temperatures have
climbed less than 5 degrees. In these locations, generally north of
I-44 in MO and I-70 in IL, afternoon temperatures are in the mid 60s
to low 70s. While areas to the south of this have had intermittent
mid-level clouds and more sunshine that has boosted temperatures
into the upper 70s to lower 80s. This is also where a low chance (20-
30%) of an isolated sub-severe thunderstorms remains this
afternoon/evening, mostly across Reynolds, Iron, and Madison
counties, as the 850mb front continues moving southward towards
southern MO. Instability is more abundant here with around 2,000
J/kg MUCAPE in place ahead of the 850mb front. However, with
effective bulk wind shear less than 15kts, any convective updrafts
will not be persistent and should struggle to grow vertically. As a
result, the main threat will be isolated wind gusts up to 40mph and
intermittent lightning.

An anomalously strong 1035mb surface anticyclone (>99th percentile
MSLP), will be sliding southeastward tonight across southern
Ontario, reinforcing northeasterly CAA into the region. This setup
will allow for the persistence of low stratus along with patches of
drizzle and mist into tomorrow morning. With widespread cloud cover
tonight, temperatures won`t fall more than a few degrees for most
with lows in the low/mid 60s forecast by tomorrow morning. It isn`t
very clear on when or if the stratus will begin to lift or scatter
out tomorrow with increasing potential for most locations to remain
enveloped in widespread cloud cover another day. Currently, the best
chance for some clearing or scattering clouds by tomorrow afternoon
is across far southern MO and further to the south. Aside for
intermittent pockets of mist that should become less prevalent
through the day tomorrow, dry conditions are expected across the
area. As a result, tomorrow may be one of the coolest days this week
for most the area with locations north of I-70 spending a majority
of the day in the mid/upper 60s while locations to the south are
forecast to reach the low to mid 70s. Any locations that manage to
clear or scatter out by the late morning/early afternoon should
warmup into the mid/upper 70s by the late afternoon.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 246 PM CDT Mon Sep 21 2026

By Tuesday night, the surface winds become more northerly instead of
northeasterly, which helps to reinforce slightly drier low-level air
into the area. This may work to scatter out any low-level stratus
that is still lingering in the area, and will also allow
temperatures to fall a bit more, especially where clearing happens.
Lows on Wednesday morning are forecast to be in the 50s across the
entire area providing the first widespread chill of the season.
Although the anomalously strong surface high is located well to the
northeast of the area, its slow moving nature maintains northerly to
easterly low-level flow across the area into the weekend. The result
for us will be a gradual warmup through the week, as clearing trends
continue, to temperatures that are near average for late September
along with dry conditions. The latest LREF temperature IQRs show
spreads of 3-5 degrees this week, illustrating higher confidence in
these values. By the weekend, there are indications from long-range
guidance that southerly flow returns to the region as a mid/upper-
level trough traverses across the western United States. A setup
like this would lead to southerly flow that would promote the return
of slightly warmer conditions and increasing chances for rain across
the region.

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 632 PM CDT Mon Sep 21 2026

Mainly MVFR ceilings are expected to perist through the period.
The only exceptions will be IFR ceilings that are expected late
tonight into Tuesday morning (07-14Z) at COU/JEF and at SUS
between 09-15Z. There will also be 3-6SM visibilities in BR at
COU/JEF/SUS during this same time frame. There is also a lower
chance (<30%) for IFR ceilings at STL/CPS. Ceilings are also
expect to improve to low VFR late on Tuesday afternoon. Winds
will remain out of the north to northeast at less than 10 knots.

&&

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

&&

$$

SHORT TERM...Peine
LONG TERM...Peine
AVIATION...Britt