Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

153
FXUS63 KLSX 121903
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
203 PM CDT Sun Jul 12 2026

.KEY MESSAGES...

- Temperatures and humidity will gradually increase through this
  week, but remain seasonable.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 156 PM CDT Sun Jul 12 2026

The surface reflection associated with a weak shortwave aloft
that was responsible for our rain chances yesterday can be seen
rotating over the Ohio Valley in current visible satellite and
regional radar imagery. With the CWA just west of this feature
and a strong ridge amplifying over the western CONUS, flow
through the depth of the atmosphere locally is mostly northerly.
This has temperatures trending slightly below normal this
afternoon despite mostly clear to partly sunny skies for most
locations, with values expected to top out in the mid 80s. As
the shortwave continues to slowly drift east-southeastward
tonight and becomes increasingly cutoff, clouds will dissipate,
with mostly clear skies expected overnight. When combined with
the light winds, much of the CWA will experience radiational
cooling, with temperatures tonight expected to be similar to
those last night (mid 60s).

&&

.LONG TERM /MONDAY THROUGH SUNDAY/...
Issued at 156 PM CDT Sun Jul 12 2026

Confidence is high in upper-level ridging prevailing across much of
the CONUS through this week, driving our weather locally. The worst
of the thermal component of the ridge will be focused across the
Northern Plains. A weak cutoff low drifting across the Mid South
will keep our flow aloft easterly, combining with the placement of
the thermal ridge to keep our temperatures seasonable for mid July.
From the middle through the end of the week, the ridge retrogrades
westward and the cutoff dissipates, allowing 850mb temperatures to
warm. As a result, our afternoon temperatures at the surface
will slowly tick upwards; starting around 90 in the beginning of
the week to end the week in the low 90s. As the ridge shifts
further westward into the weekend, flow aloft becomes
increasingly northwesterly over the Middle Mississippi Valley.
Deterministic guidance shows that there is a low chance this
flow allows for a back-door cold front to impact the region Friday
or Saturday. These types of fronts typically have a minimal
impact on temperatures and a greater impacts on dewpoints. If
the CWA does experience a FROPA, ensemble guidance supports
little to no impact on temperatures, but dewpoints do decrease.


As for rain chances, the cutoff will produce weak lift among a
seasonably unstable air mass, leading to isolated to scattered
showers and thunderstorms where it tracks. Given guidance spread
in the strength and track of the cutoff, as well as expected
variability with such a weakly forced system, confidence is low
on specifics concerning placement of rainfall. Right now, the
NBM has a 20-30% chance for showers and thunderstorms mainly
across far southeastern Missouri Tuesday-Thursday, which seems
reasonable given current guidance consensus on the track of the
low. As temperatures trend warmer toward the end of the week,
there is a low chance that the cap weakens enough as convective
temperatures are reached to produce air mass convection. Given
the low confidence in this outcome, the forecast Friday onward
has been kept mostly dry for the CWA.

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 1152 AM CDT Sun Jul 12 2026

Dry and VFR flight conditions are expected at the local
terminals through the TAF period.

&&

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

&&

$$

SHORT TERM...Elmore
LONG TERM...Elmore
AVIATION...Elmore