Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

503
FXUS63 KLSX 040754
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
254 AM CDT Sun Oct 4 2026

.KEY MESSAGES...

- Dry conditions are expected for the next week, with a gradual
  warming trend Tuesday onward.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 252 AM CDT Sun Oct 4 2026

Quiet weather conditions remain in place throughout the region,
thanks to surface high pressure and a dry, continental airmass. GOES
water vapor imagery reveals a dry shortwave moving through the Upper
Mississippi River Valley, and this feature is expected to drive a
weak cold front through the area over the course of the day today.
Given the low moisture levels present (.4-.8 inches of precipitable
water), this feature is not even expected to produce notable cloud
cover, let along precipitation, and is also not likely to impact
temperatures during the day today. Essentially, the only noticeable
weather change will be that light winds will shift from easterly to
northerly. Likewise, expect another pleasant day with temperatures
in the 70s to near 80 degrees and plenty of sun, with chilly
overnight lows again in the mid 40s to low 50s.

By tomorrow, modest "cold" air advection behind this weak front
should drop temperatures by roughly 3-5 degrees compared to today,
but this difference will be hardly noticeable. Instead, expect
another pleasant early fall day, with temperatures very near
seasonal averages.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 252 AM CDT Sun Oct 4 2026

Very little has changed regarding the long term forecast, as
northwesterly to quasi-zonal flow aloft will persist for several
days, before a broad upper ridge slowly moves east from the western
CONUS late in the week. Our forecast confidence remains high that
geopotential height rises from the slowly encroaching ridge will
result in a gradual warming trend from Tuesday onward, and
temperatures area-wide will climb back above average. Exactly how
far above average is less certain, and will depend on a number of
subtle factors.

Namely, the strength and speed of the ridge as it moves east late in
the week seems to be the biggest source of uncertainty, combined
with perhaps some bias from model forecast suites. Regarding the
former, in spite of the relatively uneventful pattern that tends to
result in a high degree of medium/long range predictability,
ensemble temperature forecast spreads remain relatively high from
mid to late week. This appears to be linked to subtle differences in
the strength of the ridge, as a stronger ridge would result in more
substantial warming. While ensemble means remain generally in the
low 80s for the most part, this comes with roughly 7-10 degrees of
spread between the 25th-75th percentile, with some notably cool
outliers still present as well. So, while we still expect (80+%) to
see multiple days of above average temperatures Tuesday onward, this
could mean anything from just a couple of degrees warmer than we are
now, to the upper 80s and maybe even touching 90 degrees again in a
few places. Not only this, but there remains some slight differences
in temperature forecasts due to model bias (namely the relatively
warm GEFS and possibly some influence from bias correction). In any
case though, these differences are relatively small, and generally
not impactful in a practical sense.

Otherwise, low humidity will persist for the foreseeable
future, and there remains very little opportunity for
precipitation for the next week. This may change next week as it
appears that the ridge will give way to southwest flow again as
it moves east, but confidence in the timing of this transition
remains low.

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1240 AM CDT Sun Oct 4 2026

VFR conditions are expected throughout the 06Z TAF period. A few
patches of shallow fog are possible at river valley terminals
(JEF/SUS/CPS) early this morning but this is not expected to be
impactful. Calm surface winds overnight will become light and
northerly this afternoon as a weak cold front passes through the
area, with only a few passing high clouds expected.

&&

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

&&

$$

SHORT TERM...BRC
LONG TERM...BRC
AVIATION...BRC