Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

152
FXUS63 KLSX 181108
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
608 AM CDT Thu Jun 18 2026

.KEY MESSAGES...

- Aside from isolated/scattered showers today, largely dry
  conditions are expected through Friday.

- Opportunities for showers and thunderstorms exist Saturday
  through early Monday, with the highest chance on Sunday
  accompanied by a low threat of locally heavy rainfall.

- Temperatures will vary from near to below average through mid-
  next week.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 319 AM CDT Thu Jun 18 2026

A few showers and thunderstorms are expected to continue at times
through daybreak across southeastern MO/southwestern IL until the
front departs by around mid-morning, but weak convergence and
displacement from the LLJ will limit coverage. A combination of weak
mid-level isentropic ascent and strengthening FGEN will force
additional isolated to scattered post-frontal showers, perhaps a
rumble of thunder, late morning through the afternoon that sweep
through the area. However, low-level advection of a drier and much
cooler airmass will limit how much precipitation reaches the ground
and is measurable. The highest chances of (light) measurable
rainfall per the HREF are 20 to 40 percent near the I-70 corridor.
Associated cloud cover and this cooler airmass will result in much
cooler (10 to 15 F) high temperatures compared to Wednesday, in the
mid-70s to low-80s F for most areas.

A surface high pressure center will migrate into the CWA late
tonight through Friday beneath gradual mid-level height rises.
Resulting mostly clear skies and calm/light winds will allow low
temperatures Friday morning to reach the mid-50s to low-60s. Patchy
radiation and/or steam fog, mainly in river valleys, is possible
with these temperatures flirting with forecast crossover
temperatures and around 20 F cooler than river water temperatures.
High temperatures will be warmer on Friday and around 80 to the mid-
80s F given strong insolation expected through only thin upper-level
clouds, despite an absence of WAA during the day.

Pfahler

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 319 AM CDT Thu Jun 18 2026

Late Friday through early Monday, upper-level northwesterly flow
will transition to quasi-zonal across the Mid-Mississippi River
Valley, providing one or more additional opportunities for showers
and thunderstorms as moisture slowly returns with incremental
northward advancement of a front and a series of upper-level
shortwave troughs/perturbations pass. Ensemble model guidance has
the greatest support for showers and thunderstorms in the late
Saturday night through Sunday evening timeframe coinciding with a
more prominent shortwave trough. There are also mixed signals for an
MCS to initiate across the Central Plains late Saturday, arriving in
the Mid-Mississippi River Valley or Ozarks on Sunday. Lower
resolution global models have been struggling to resolve this MCS
and its associated MCV partially due to suspected convective
feedback issues, which introduces significant uncertainties on the
longevity, track, and timing of the MCS and the influence of those
factors on the overall surface and upper-level pattern.  With the
aforementioned uncertainties, the NBM interquartile high temperature
range is also nearly 10 F on Sunday, spanning the low-70s to mid-80s
F. It is also worth mentioning that although the chances of showers
and thunderstorms are 70 to 90 percent throughout Sunday, it is
unlikely that it will rain the entire day.

With PW projected to exceed the 90th climatological percentile in
addition to a potentially favorably oriented front and
aforementioned MCS, there is at least a low threat of locally heavy
rainfall Saturday night into Sunday. This threat is supported by a
signal in the ECMWF EFI/SOT for extreme rainfall, but it has been
highly variable from run to run and highest values are generally to
the west of the CWA. Additionally, there could be some threat of
severe weather, but this threat appears even more conditional and
with lower confidence.

Monday through mid-next week, global model guidance is in agreement
that the front will shift back south of the CWA as upper-level flow
also becomes northwesterly once again. As a result, temperatures
will return back to below average and largely dry conditions will
prevail.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 608 AM CDT Thu Jun 18 2026

Dry and VFR flight conditions will exist most of the TAF period.
Scattered showers are expected late this morning into the afternoon,
mainly along/just north of the I-70 corridor. However, confidence is
low in any categorical reductions at the terminals, although a
stray lightning strike or two is possible. Late tonight/Friday
morning, conditions could become favorable for some patchy river
valley fog but confidence is not high enough to include at the
juncture.

Pfahler

&&

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

$$

WFO LSX