Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

336
FXUS63 KLSX 181806
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
106 PM 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 Night)
Issued at 106 PM CDT Thu Jun 18 2026

Light rain and isolated thunderstorms are expected to continue
moving southeast along a slow-moving, east-west oriented cold front
through 00z. Rain chances (20-40%) will mainly lead to low impacts
to locations south of I-70 through 00z. Isolated thunderstorms are
possible along the front, leading to very brief downpours.

The region is positioned at the southern edge of a longwave,
upper level trough this afternoon with a secondary surface cold
front following close behind last night`s front. Radar trends from
this morning through early afternoon show precipitation tracking
southeast around 20-25 mph with isolated thunderstorms
occasionally developing within the east-west oriented band of
precipitation. Hi- res and medium range guidance has had
difficulty in placement and overall intensity with the NAM
seemingly best suited for timing and hi-res guidance more
representative of intensity. None of the hi-res guidance seems to
be picking up on the limited convective potential, while the
NAM/GFS show low MUCAPE values (100-300 J/kg) along and south of
I-70 through approximately 00z. Thunderstorms will be very short-
lived at any one location with a brief downpour. Thunderstorms
remain isolated with precipitation duration lasting approximately
2 hours from start to finish, give or take 30 minutes. Rainfall
amounts only amount to around 0.10" or less.

Cooler air and lower dewpoints have already begun to infiltrate
the region behind last night`s front. Where rain falls this
afternoon, temperatures will be relatively cooler (mid to upper
70s) than dry locations (low-80s). Surface high pressure builds in
behind the front from the northwest tonight through Friday. Quiet
and dry conditions hold through the end of the short term period
with seasonably cool temperatures (Highs: low/mid-80s; Low: Upper
50s to mid-60s).

Maples

&&

.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 18z TAFs through 18z Friday Afternoon)
Issued at 1159 AM CDT Thu Jun 18 2026

VFR conditions are largely expected through the TAF period with
light surface flow. A secondary cold front follows close behind
last night`s cold front, resulting in showers and isolated
thunderstorms. Lightning detection shows thunderstorms are limited
enough not to include in the prevailing groups with TEMPOs used
to track precipitation through from northwest to southeast.
Precipitation will last 1-2 hours at impact terminals (all site
with exception to KUIN) with a 1 hour buffer built in. -TSRA will
be addressed via amendments. Outside of any thunderstorms,
surface observations show vsby at or above MVFR thresholds. This
potential is expected to wane and/or pass to the south of the
terminals by 22z with quiet and dry conditions thereafter.

Maples

&&

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

$$

WFO LSX