Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

515
FXUS63 KLSX 040323
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1023 PM CDT Mon Aug 3 2026

.KEY MESSAGES...

- More seasonable temperatures will return this week along with
  dry conditions through Tuesday.

- The chance of showers and thunderstorms peaks at 60 to 80
  percent between Wednesday afternoon through Thursday night.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 235 PM CDT Mon Aug 3 2026

A surface high pressure center, located across central IL this
afternoon, will continue to very slowly migrate eastward through
Tuesday, permitting another round of river valley fog across the
Ozarks/southeastern MO into southwestern IL late tonight into
Tuesday morning where conditions are most favorable closer to the
departing high pressure center. Weak low-level southerly flow/WAA
will spread into much of the CWA by Tuesday afternoon with high
temperatures on Tuesday several degrees warmer than today and in the
mid-80s to low-90s F further aided by strong insolation through
diurnal cumulus ahead of arriving mid/upper-level clouds during the
evening.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 235 PM CDT Mon Aug 3 2026

Tuesday night through Thursday, an upper-level longwave trough will
become established across the Northern Plains and Upper Mississippi
River Valley with multiple shortwave troughs/perturbations at its
base nudging a cold front southward into the CWA Wednesday. A few
CAMs suggest that showers and thunderstorms will be ongoing across
IA into northern MO Wednesday morning at the nose of a diminishing
LLJ, but additional or renewed development is forecast during the
afternoon and evening near the cold front across northeastern MO and
west-central IL. With 25 to 35 kt of deep-layer wind shear near the
front, there is the potential for a few strong to severe
thunderstorms, but there is some uncertainty in the amount of
instability due to variations in BL moisture and the impact of the
early day precipitation/clouds. For context, the interquartile range
of global ensemble model SBCAPE approximately spans 500 to 2000
J/kg. Regardless, some upscale growth/increasing coverage of
thunderstorms is expected Wednesday evening into overnight
considering a large parallel front-shear component, with a
seasonably strong nocturnal LLJ providing maintenance overnight.
With deep-warm cloud depths and anomalous precipitable water (80 to
90th climatological percentile), there is at least a low threat of
locally heavy rainfall Wednesday night into Thursday morning with
front being slow-moving and conditional interface of the LLJ with
the southern flank of an MCS. However, the confidence needed to
message severe weather or flash flooding at this time range is not
yet high enough.

On Thursday, the cold front will stall somewhere across the CWA with
moisture further increasing/pooling along it, providing at least
isolated redevelopment of showers and thunderstorms during the
afternoon or evening, perhaps increasing in coverage overnight as
another, albeit weaker, LLJ develops. After Thursday, model
guidance is in agreement that the upper-level longwave trough
will become more retracted to Canada and the far-northern CONUS.
As more active mid-level flow lifts northward and a potential
weak cutoff low migrates eastward of the Mid- Mississippi River
Valley, ensemble model probabilities of showers and
thunderstorms decrease each day through the weekend. Less and
less precipitation/clouds and increasing low-level southerly
flow will permit an eventual warming trend back to above
average, but it is uncertain how quickly this drying and
warming takes place, reflected by a 5 to 8 F interquartile
temperature spread in the NBM through the weekend.

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1023 PM CDT Mon Aug 3 2026

VFR conditions will continue to prevail with light winds and dry
surface conditions as a high pressure system continues to make it`s
way east through the region. The exception to this is a chance of
river valley fog late tonight and into early Tuesday morning that
will primarily impact SUS and CPS.

&&

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

&&

$$

SHORT TERM...Pfahler
LONG TERM...Pfahler
AVIATION...Asel/Elmore