Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

634
FXUS63 KLSX 252006
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
306 PM CDT Thu Jun 25 2026

.KEY MESSAGES...

- Showers and thunderstorms capable primarily of heavy rainfall
  are expected through Friday evening, with a Flash Flood Watch
  remaining in effect for much of the area.

- Thunderstorms both Thursday and Friday afternoon and early
  evening will also be capable of isolated instances of damaging
  wind gusts and large hail.

- Dangerous heat and humidity will build into the region on
  Sunday and continue through much of next week.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 304 PM CDT Thu Jun 25 2026

A cold front has settled into the region, with current surface
observations showing it roughly along/just north of I-70; just north
of the cumulus field seen in visible satellite. Ample insolation
south of the front has yielded upwards of 2,000 J/kg of MLCAPE.
Thanks to subtle lift from an approaching disturbance, forcing from
the front, and the building instability, isolated to scattered
showers and thunderstorms have developed along the I-70 corridor
across both Missouri and Illinois. Effective bulk shear is around 30
kts along the portion of the front in Illinois, but is expected to
increase to that value across Missouri through the rest of this
afternoon. This favors an updraft or two becoming organized, with a
threat of brief supercellular structures. The strongest updrafts
will be capable of large hail and damaging wind gusts.

The previously described convective activity will be occurring ahead
of an approaching shortwave and associated convective complex
currently seen over eastern Kansas. As this complex moves into the
CWA this evening, PWAT is forecast to be around 1.75", paired with
slow storm motions and deep warm cloud layers to support a threat of
heavy rainfall. With thunderstorms repeatedly impacting the same
areas, the threat of flash flooding remains a concern through early
Friday morning.

Convective trends become increasingly uncertain mid-morning Friday
onward, with guidance diverging in the strength on the strength of
the surface low associated with this initial disturbance. A minority
of guidance shows a stronger low that would push the front south of
the CWA and greatly limit the chance for additional convection
across much of the CWA tomorrow. A majority of guidance favors a
weaker low, that will have little impact on the position of the
front as a trailing MCV moves across the region during the day
tomorrow. This solution will keep the warm sector mainly along and
south of I-70, with the MCV enhancing lift and shear as it moves
through the CWA. The current expected trajectory of the MCV
highlights southeastern Missouri and southwestern Illinois for
isolated to scattered severe thunderstorms capable mainly of
damaging wind gusts and large hail, with a low chance for tornadoes.
Given that a majority of guidance favors this solution, it is
reflected in the current forecast. The atmosphere over the CWA will
remain conducive for heavy rainfall with this solution as well, with
the Flash Flood Watch now being extended through Friday evening.
Subsidence in the wake of the MCV and diminishing instability will
lead to a downward trend in convection during the early evening
Friday, with a lull expected during the overnight hours.

Elmore

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 304 PM CDT Thu Jun 25 2026

On Saturday, upper-level ridging will gradually build into the
Midwest. This will push the stationary front that will have been
draped across the area in the previous days northward; however,
confidence is low in how quickly this will happen through the day.
The speed of the now warm front lifting northward will impact
placement of convective potential through the day and primarily
during the afternoon. While height rises thanks to the building
ridge would suppress convection, there is enough of a consensus
among deterministic guidance in a weak shortwave cresting the ridge
during the afternoon that will amplify lift along the front and lead
to a 30-50% chance for scattered showers and thunderstorms. If the
front is slower to lift north, this chance for showers and
thunderstorms will be across a majority of the CWA, while a faster
front will limit convective potential roughly along and eastward of
the Mississippi River.

For Sunday onward, the main focus will the threat of dangerous
levels of heat and humidity. Guidance consensus remains strong in
the upper-level ridge rapidly building northward across the Midwest
as 850mb temperatures surge to into the mid-20s C. The result at the
surface will be temperatures in the mid-90s, with uninhibited flow
from the Gulf and local evapotranspiration supporting dew points in
the mid 70s. These temperatures and dew points will combine to push
heat index values at least into the 100-105 degree F range (80%
chance) through Thursday. The ridge is forecast to be strong enough
to minimize convective impacts to the heat, and nearly every
ensemble member keeps the area dry through this portion of the
period.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1246 PM CDT Thu Jun 25 2026

A large cluster of thunderstorms will approach the region late
this afternoon and evening. Ahead of this cluster, isolated to
scattered showers and thunderstorms are expected mainly around
KCOU, KJEF, KSUS, and KCPS. The cluster itself will be capable of
more persistent, prolonged impacts. These impacts will mainly be
visibility reductions and frequent lightning, though there is a
low chance for strong, erratic wind gusts. While the chance for
thunderstorms is over a long period in all of the TAFs, there is a
low chance that it is not long enough, and chances may linger
later into tomorrow morning. Even if storms move out of the space
of the local terminals, low stratus will be present. Confidence is
high in at least MVFR ceilings, with a low chance for IFR
ceilings.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Friday evening 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 through Friday evening 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