Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

042
FXUS63 KLSX 251130
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
630 AM CDT Thu Jun 25 2026

.KEY MESSAGES...

- Showers and thunderstorms capable of heavy rainfall are
  expected this afternoon into tomorrow morning. A Flash Flood
  Watch remains in effect for much of the area.

- A few thunderstorms this afternoon may become strong enough to
  produce damaging winds.

- Potentially dangerous heat and humidity will build into the
  region starting Sunday and continue through next week.


&&

.SHORT TERM...THROUGH SATURDAY/...
Issued at 126 AM CDT Thu Jun 25 2026

A weak cold front has dropped into the Mid Mississippi Valley
and will slowly ooze south today beneath quasi-zonal flow aloft.
Most of the CAMs believe that this front will continue to provide
enough forcing to squeeze out isolated to widely scattered
thunderstorms. With an atmosphere characterized by 1000-2000
J/kg of MLCAPE and 25-35 kts of deep layer wind shear, a few of
these storms may become organized enough to produce damaging
winds.

This evening and overnight, a shortwave currently over the
Intermountain West will approach the region. This disturbance
will spur low level cyclogenesis over the Central Plains, which
in turn will establish a low level jet from eastern Texas
through Missouri. The resultant deep moist convection at the
interface of the low level jet and the stalled front will
initiate widespread convection along the front. Given
precipitable water approaching 2", warm cloud depths around
10,000`, modest instability and wind shear, and the potential
for training storms along the front, this is a classic setup
for very heavy rainfall and flash flooding.

Indeed, both the 18z REFS and 00z HREF LPMM show a stripe of
3-5" of QPF across the southern half of Missouri, though both
models have pushed the heavy rain a bit further south than
previous runs. I suspect the forecast for the heaviest rain will
continue to waver somewhat due to the low predictability of the
frontal positioning. Wherever the heavy rain does fall, it will
be enough to generate at least isolated flash flooding. If the
rain overachieves, or if it impacts an areas susceptible to
flash flooding (urban/suburban areas), the flooding could be
more widespread or impactful.

After sunrise on Friday morning, the shortwave will depart to the
east and the low level jet will dissipate, resulting in a rapid
decrease in thunderstorm coverage. Nevertheless, the stalled front
will remain across the region and several of the above factors
supportive of heavy rainfall will still be in place. So while
thunderstorm coverage is expected to be less on Friday, the threat
for flash flooding may extend into at least the afternoon. An
extension of the watch may be needed once models come into better
consensus on where this additional convection will occur.

&&

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY/...
Issued at 126 AM CDT Thu Jun 25 2026

Upper level ridging will begin to build into the region on Friday,
and will continue to amplify through the weekend. This help push the
above front to the north through the region, which may result in one
more round of convection on Saturday before departing the Mid
Mississippi Valley. Behind the front, deep, persistent warm air
advection will push 850mb temps into the mid 20s C beneath 500mb
heights in excess of 590 dam. These values are typically associated
with heat waves, and the latest guidance is indeed coming in quite
hot from Sunday through the middle of next week. Model guidance
is conspicuously devoid of through much of that period,
increasing confidence that we will see out first significant
heat episode of the year.

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 602 AM CDT Thu Jun 25 2026

Largely-VFR conditions currently exist at the regional terminals
ahead of a cold front that is stalled north of or just near a line
from KIRK to KUIN, though IFR fog is impacting a few airports
south of the Missouri River. As the day goes on, fog will
dissipate but instability will build and lead to a threat for
scattered thunderstorms during the afternoon.

The front advances south this evening but again stalls, setting
the stage for numerous rounds of convection in the vicinity of the
I-70 corridor affecting the central Missouri and St. Louis
metropolitan terminals. While thunderstorms can also be expected
at KUIN, impacts should be a bit more limited that far north. As
moisture pools along the front, CIGs are also forecast to lower.
While some guidance suggests IFR/LIFR conditions, that is
climatologically very unlikely. The TAFs do degrade conditions to
MVFR, and while I can`t rule out brief instances of IFR overnight,
most of the time visual flight rules should prevail.

MRB

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch from 1 PM CDT this afternoon through Friday morning
     for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Lincoln MO-
     Madison MO-Moniteau MO-Montgomery MO-Osage MO-Pike MO-
     Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis
     City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO-
     Washington MO.

IL...Flood Watch from 1 PM CDT this afternoon through Friday morning
     for Bond IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-
     Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-Washington
     IL.

&&

$$

WFO LSX