Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

776
FXUS63 KLSX 250534
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1234 AM CDT Thu Jun 25 2026

.KEY MESSAGES...

- Showers and thunderstorms capable of heavy rainfall are expected
  Thursday afternoon into Friday morning. A Flash Flood Watch has
  been issued for portions of the area.

- Heat and humidity will build into the region starting Sunday
  and continue through next week.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 1227 AM CDT Thu Jun 25 2026

(Through Late Thursday Night)
Issued at 207 PM CDT Wed Jun 24 2026

Current water vapor imagery shows broad, shallow troughing across
the eastern CONUS with an upper level ridge over the Desert
Southwest. This has the CWA beneath weak northwesterly flow aloft,
with multiple disturbances within this flow moving into the
Midwest. A surface low associated with one of these disturbances
is traversing the Midwest well north of the CWA, placing the CWA
beneath warm air advection. This warm air advection is responsible
for the ongoing isolated to scattered showers and thunderstorms.
As this wing of warm air advection pivots eastward, the focus for
the convection will also shift east-southeastward through this
evening, dissipating by mid evening with instability decreasing.
The main threats with this convection will be brief heavy rainfall
and frequent lightning. Current ACARS soundings and SPC
Mesoanalysis show that this convection is occurring on the leading
edge of more favorable instability and shear, and is expected to
remain outside of these favorable conditions due to a lack of
forcing.

The aforementioned surface low`s attendant cold front will slowly sag
southward toward the CWA overnight, and has a low chance of forcing
weak convection for areas along and north of Highway 36/I-72.
However, the main period of focus for convection along this front is
Thursday afternoon into Friday. Then, the front will have stalled
somewhere along the I-70 corridor as disturbances within the zonal
flow aloft ripple overhead. This will lead to multiple rounds of
showers and thunderstorms along the front as early as mid-day
Thursday and continuing through late Thursday night.

Guidance consensus is that SBCAPE will be around 1,500 J/kg and deep-
layer shear around 25 knots will support a low chance for brief
updraft organization along and south of the front. A majority of
deterministic soundings show a weak inverted "V" signature near the
surface, favoring isolated damaging wind gusts. However, with PWAT
around 1.75" (~75th percentile), warm cloud depths, and slower storm
motion, the main threat with convection will be heavy rainfall and
flash flooding. The zonal flow aloft paired with the stalling front
leads to uncertainty in specifics on the exact location of this
threat, with there still being enough lead time for it to shift
north or south. Where confidence is greatest in totals quickly
reaching 2-3", with isolated 4-6", a Flash Flood Watch has been
issued through Friday morning.

Elmore

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 1227 AM CDT Thu Jun 25 2026

(Friday through Next Wednesday)
Issued at 207 PM CDT Wed Jun 24 2026

The pattern on Friday is forecast to be similar to that on Thursday,
leading to continuing chances for rainfall through the day. However,
confidence is very low in the coverage and intensity of rainfall.
Some guidance has an MCS moving through the CWA very late Thursday
night/early Friday morning, and if this happens, then rain chances,
coverage, and intensity will remain lower through the day Friday.
However, if this does occur as some guidance suggests, then
additional showers and thunderstorms will occur through the day
along the front. These will be capable of heavy rainfall, and would
prompt an extension of the Flash Flood Watch. The front will begin
to buckle northward on Saturday as upper-level ridging noses into
the lower Midwest, though how quickly it moves northward varies
among guidance. A slower moving front favors rain chances continuing
through much of the day, while a faster front will end rain chances
by late morning.

Starting Sunday, both deterministic guidance and ensemble clusters
depict the upper-level ridge rapidly amplifying over the Midwest.
This will pull the front responsible for the late week and early
weekend rain chances well to the north, opening the door for deep
warm air advection. Ensemble means are clustered around 850mb
temperatures in the low to mid 20s C, climatologically favoring
surface temperatures in the low to mid 90s F. With a majority of
guidance favoring this solution, confidence is high in a multi-day
stretch of hot and humid conditions next week. Impacts from
potential convection at this point seem few to none thanks to the
ridge`s axis being centered over or just east of the CWA and the
crest of the ridge well north of the area, keeping robust convective
activity well displaced from the CWA.

Elmore

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1227 AM CDT Thu Jun 25 2026

There will be multiple rounds of thunderstorms throughout the
TAF period associated with a cold front sagging through the
region. This first round has already started with
isolated/scattered storms in the vicinity of KUIN. These storms
will persist on and off through the day as the front oozes to
the south, and should be near all of the other terminals by the
late morning or afternoon. I`ve added a prob30 group for those
TAFs when I think the storms are the most likely, but they are
possible pretty much at any point through the day.

More widespread thunderstorms are expected to develop sometime this
evening and should persist through much of the night. Again,
it`s difficult to pinpoint exactly when the storms will impact
each terminal, but I`ve included a period of prevailing
thunderstorms when they appear to be the most likely. The
exception to this is at KCPS and KSUS where I expect the most
widespread storms to hold off until after 06z.

The other concern is the potential for MVFR cigs with the onset
of the more widespread storms. I`ve kept this out of the TAFs
for now, but may need to be included in subsequent forecasts.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch from this afternoon through Friday morning for
     MOZ041-047>052-059>065-072-073.
IL...Flood Watch from this afternoon through Friday morning for
     ILZ058>060-064-065-069-070-074-098>102.

&&

$$

SHORT TERM...
LONG TERM...
AVIATION...BSH