Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

289
FXUS63 KLSX 240717
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
217 AM CDT Wed Jun 24 2026

.KEY MESSAGES...

- Waves of showers and thunderstorms are forecast through
  Saturday across the region, with the highest chances (70-90%)
  Thursday evening through Friday.

- Thursday evening through Friday morning will also see the
  greatest threat for excessive rainfall and flash flooding,
  particularly along and south of the I-70 corridor/Lower Missouri
  River Basin and associated tributaries.

- Hot and humid conditions, potentially the warmest weather we`ve
  seen so far this year, are increasingly likely Sunday through
  the end of June.

&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 215 AM CDT Wed Jun 24 2026

With a surface ridge axis to our east centered north of the Ohio
River Valley, weak return flow is bolstering temperatures and dew
points across the region. To our north associated with a mid-level
shortwave tracking through the northern CONUS, a meager cold front
is forcing scattered convection across the Upper Mississippi River
Valley. This front will continue to make southward progress
overnight and, by most short-range guidance depictions, arrive in
northern Missouri later this morning. High-resolution guidance
continues to depict surface dewpoints pooling ahead of the front
which, combined with meager yet sufficient low-level forcing and
negligible upper-level ascent, will result in scattered weak
convection across most of the region. While most of the region will
be under some threat for thunderstorms, there will likely be plenty
of dry time as the front oozes southeast and drags the weak
convection along with it. Otherwise, cloud cover and the lack of
warm advection will keep temperatures seasonably cool yet again.

By all accounts, the front fails to completely pass through the
forecast area. There is increasing consensus among available
guidance that the baroclinic zone will hang up somewhere along the I-
70 corridor to the Missouri River in an east-west orientation
tonight into Thursday morning. This front will be the focus for at
least isolated to widely-scattered showers and weak thunderstorms
during the day on Thursday. I cannot rule out a few stronger
thunderstorms on the warm and unstable (1000-1500J/kg of weakly-
capped MLCAPE) side of the boundary, mainly across the Ozarks, which
would threaten wind gusts up to 50mph. Most of the activity will
likely not amount to anything too impactful, and any rain that falls
will prime the ground for the increased heavy rain threat later
Thursday evening into Friday along this front.

MRB

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 215 AM CDT Wed Jun 24 2026

Amidst the quasi-zonal flow that most global-scale guidance depicts
overhead on Thursday, a stronger wave is consistently being modeled
to track along the baroclinic zone later in the day. Exactly how
fast and how potent that wave will be is still not clear, but there
is increased potential that this wave will interact with
precipitable water values exceeding the 90th climatological
percentile (per LREF and REFS guidance) and a strengthening LLJ
intersecting the front. These synoptic-scale features, favorable for
heavy and efficient rain, are made more favorable by the deep warm
cloud depths (10-12kft per most higher-resolution guidance) and high
RH within those cloud depths. All of this is to say the environment
will be primed for heavy rain and at least some degree of localized
flooding where these storms track. The greatest source of
uncertainty surrounds where the axis of heavy rain will exist, which
is tied closely to where that baroclinic zone settles.

REFS LPMM output suggests a narrow swath of localized 3.00-4.00"+
values with a broader 1.00-2.00" values after all is said and done
on Friday, which is a reasonable scenario given the favorable
pattern and thermodynamic environment. While flash flooding, and
perhaps additional rises on the Missouri River and its tributaries,
is increasingly likely, the pretty drastic uncertainty surrounding
the rainfall axis location (upwards of 75-100 miles north or south)
precluded a Flood Watch issuance with this forecast package. It is
becoming increasingly likely that one will be needed soon, hopefully
accompanying some increased clarity in the heavy rain location.

The wave gradually departs to our east on Friday, leaving the Mid-
Mississippi Valley in a dearth of upper-level ascent and
resulting in a downward trend in convective coverage and
intensity. The stalled front remains in place, however, which
keeps a threat for at least scattered showers and thunderstorms
along with it. While timing differences exist, deterministic
guidance and their ensemble counterparts agree that the front
lifts north as an upper-level ridge amplifies over the central
CONUS on Saturday and low-level warm advection intensifies. Rain
chances shunt north as a result, but a noteworthy warmup takes
hold of the region Sunday through the end of June. ECMWF EFI
output doesn`t suggest high temperatures will be particularly
extreme (above the 90th model climatological percentile), though
it does paint some higher chances of very abnormally-warm
overnight lows. Regardless, with 500mb heights exceeding the 90th
climatological percentile according to global- scale ensembles and
850mb temperatures even more anomalous than that, we may see our
hottest conditions of the year so far. LREF and NBM temperature
interquartile ranges are both fairly tight, though the
distributions themselves differ a bit. This likely stems from some
uncertainty around cloud cover and convective activity on the
periphery of the strong upper-level ridge. Combined with dewpoints
that are fairly uniformly in the low to mid-70s in most available
guidance, this has the potential to result in dangerous heat as
outdoor activities ramp up for Independence Day.

MRB

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1144 PM CDT Tue Jun 23 2026

VFR conditions will prevail overnight tonight ahead of a weak cold
front currently dropping south across the Upper Mississippi
Valley. As it reaches the Mid-Mississippi Valley later this
morning, sufficient instability and low-level moisture will
likely be available to initiate scattered convection along it
during the late morning and afternoon. KUIN remains largely
unlikely (10-15% chance) to see thunderstorms before the front is
south of the terminal, but there is an increased threat at the
central Missouri and St. Louis metropolitan terminals. Given the
scattered nature of the storms, PROB30s were kept at these sites
and amendments will be made if a more concrete threat exists at
the terminals. Following the frontal passage, VFR conditions
resume through the remainder of the TAF period.

MRB

&&

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

$$

WFO LSX