Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

425
FXUS63 KLSX 030940
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
440 AM CDT Mon Aug 3 2026

.KEY MESSAGES...

- Temperatures are expected to warm back closer to seasonal
  averages this week.

- A slow-moving cold front brings our best chances (60-80%) of
  showers and thunderstorms Wednesday afternoon through Thursday
  night.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 219 AM CDT Mon Aug 3 2026

A weak surface ridge of high pressure is centered across
central Missouri early this morning and will slowly slide east
through tonight. Plenty of sunshine is expected today, other
than some diurnal fair-weather cumulus. The sunshine today will
help high temperatures to warm into the mid 80s, just a few
degrees below seasonal normals. Lows tonight are expected to
drop back into the 60s beneath a mostly clear sky and
light/variable winds.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 219 AM CDT Mon Aug 3 2026

(Tuesday - Tuesday Night)

The surface ridge is expected to move far enough east by Tuesday
that weak return flow will begin in its wake. The moderating trend
in temperatures is therefore expected to continue as highs reach
closer to the 90 degree mark. Increasing mid/high level clouds will
help dampen the warmup slightly during the day, but then aid in
keeping temperatures milder Tuesday night as lows only drop back
into the mid 60s to low 70s from east to west.


(Wednesday - Sunday)

A broad longwave trough is forecast to carve out across the northern
Plains/southern Canada by midweek. Multiple impulses are expected to
move across the base of this trough, with each one inducing weak
cyclogenesis along a slow-moving cold front. This boundary is
forecast to move into portions of the area by Wednesday afternoon.
Surface convergence along this boundary in addition to increasing
low-level moisture convergence and mid/upper level diffluence aloft
is expected to yield showers and thunderstorms. The best chances (60-
80%) through Wednesday night are across northeast Missouri and
west-central Illinois in close proximity to the expected location of
the surface cold front. There may be at least a low threat for a few
strong to severe thunderstorms in the afternoon/evening hours given
fairly strong westerly flow aloft for early August. Joint
probabilities on the LREF for at least 1000 J/kg of MUCAPE and 30+
knots of deep-layer shear are 40-50% early Wednesday evening in
northeast Missouri/west central Illinois. Precipitable water values
approach 1.8" along the front (>90th percentile of climatology). The
slow equatorward progress of the cold front Wednesday night into
Thursday in conjunction with a strengthening nocturnal low-level jet
(850-hPa meridional/v component of wind >90th percentile) also
suggest at least the possibility of locally heavy rainfall/isolated
flash flooding.

There is pretty good consensus that the front will move toward
southeast Missouri/southwest Illinois, but may tend to stall out.
Deterministic guidance has a weaker low-level jet Thursday night,
but increasing moisture convergence may help yield an uptick in
shower and thunderstorm activity along/north of the front.

The location of the boundary Friday through the weekend becomes
cloudier with time. Multiple possibilities exist. Some deterministic
guidance pushes the front back north, which would likely yield
warmer, but dry conditions. Another scenario is that the front
lingers across the area and help provide the focus for additional
showers and thunderstorms. The boundary also could be modulated
farther south due to antecedent rounds of convection. The bottom
line is that forecast specifics, both in terms of temperatures and
precipitation chances, are uncertain right now.

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 437 AM CDT Mon Aug 3 2026

River valley fog will continue over the next few hours, but
should improve rapidly after sunrise. Dry/VFR conditions are
expected thereafter along with light/variable winds through
tonight.

&&

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

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Gosselin