Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

342
FXUS63 KLSX 231943
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
243 PM CDT Thu Jul 23 2026

.KEY MESSAGES...

- Cooler temperatures will continue through Friday before the heat
  and humidity return areawide late this weekend.

- Showers and a few thunderstorms are expected Friday through
  Saturday morning, mainly in central/southeast Missouri.
  Locally heavy rainfall is possible.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 242 PM CDT Thu Jul 23 2026

Strong surface high pressure over the western Great Lakes
continues to supply dry, cool easterly flow into the mid-
Mississippi Valley. A few light rain showers have attempted to
move eastward during the day today, but have dissipated due to a
lack of instability and lack of stronger forcing aloft. I
cannot rule out a few stray sprinkles late this
afternoon/evening, but by and large dry weather is in store for
much of tonight with lows in the mid 60s.

Widespread showers and thunderstorms are forecast to develop late
tonight across eastern Kansas and western Missouri. This activity
should be able to survive a bit better than today, mainly due to a
strong midlevel shortwave trough being a primary forcing mechanism.
Therefore, at least scattered (light) rain showers should move into
central Missouri early Friday morning. A rumble of thunder cannot be
ruled out given the time of year, but deterministic guidance shows
barely any MUCAPE so kept thunder probabilities isolated in
coverage. Temperatures will be quite cool for mid/late July due to
the aforementioned rain chances and increase in cloud cover. Most of
the area should stay in the 70s, with some locations in
central/northeast Missouri potentially only topping out in the low
70s due to the earlier onset of the thicker cloud cover.

There remains some uncertainty with the exact track of the midlevel
shortwave trough Friday night into early Saturday morning, along
with the location/strength of the low-level jet. The ECMWF remains a
northern outlier, but most CAMs as well as the GFS are farther
southwest and focus the rain mainly across southeast Missouri. This
seems like the most plausible solution given the MUCAPE gradient to
our southwest. There remains the possibility of locally heavy
rainfall/isolated flash flooding given anomalously high precipitable
water values (~2", >95th percentile of climatology) and deep warm
cloud depths. Showers and thunderstorms could also tend to train
from north/northwest to south/southeast late Friday night into early
Saturday morning as the low-level jet veers with time. The main
negating factor for heavy rainfall continues to look like relatively
modest elevated instability (i.e., lack of deep convection). In the
absence of deep convection, the rainfall rates just won`t be high
enough to produce flash flooding. However, if the MUCAPE gradient
were to shift farther north/northeast, that would increase the
threat into our area. The low-level jet also looks pretty modest
(~20 knots). More specifically, the v component (north-south) of the
wind at 850 hPa is only near the 75th percentile of climatology on
the NAEFS. Above normal, yes, but not particularly strong or
noteworthy. Widespread rainfall totals of 0.50-1.25" are expected
across central/southeast Missouri, though the potential at least for
some training does suggest some isolated totals up to 2-3+" are
possible. These higher-end potential totals are supported by the
REFS/HREF LPMM, but may tend to stay deeper into the higher
instability aloft and to our southwest if they occur.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 242 PM CDT Thu Jul 23 2026

(Saturday Night - Tuesday)

We will quickly transition from a cool and rainy pattern for some to
heat and humidity by the end of the weekend as the mid/upper level
ridge amplifies and shifts eastward. Temperatures at 850 hPa climb
close to +25C, or near the 99th percentile of climatology.
Confidence is increasing in widespread 100-105+ heat index values
each day beginning on Sunday lasting through Tuesday. Magnitude heat
advisory criteria will probably be reached across portions of the
area on one or multiple days, but we are far enough out still to
hold off on the issuance of heat products. The other potential fly
in the ointment is a low threat of showers/thunderstorms moving in
from the north. There is very little signal in deterministic model
guidance attm, but the mid/upper level anticyclone itself does stay
to our west. In addition, forward-propagating Corfidi vectors are
mostly northerly, so IF a complex gets organized to our north it
could move into our region. Depending on the timing, this could
knock down the heat on any given day, but also would threaten us
with damaging wind gusts.


(Tuesday Night - Next Thursday)

Forecast uncertainty begins to increase by the middle of next week
as ensemble guidance is in pretty good agreement that the anomalous
mid/upper level ridge will weaken slightly and shift back to the
southwest. This should at least increase the threat of a backdoor
cold front and/or a ridge-running shortwave to produce
showers/thunderstorms. Either of these scenarios would at least
slightly cool temperatures and take the edge off of the heat.
However, there are no strong signs through at least next Thursday of
a strong air mass change. Therefore, in the absence of a backdoor
cold frontal passage or showers/thunderstorms, it is possible the
heat/humidity will continue past Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1218 PM CDT Thu Jul 23 2026

Scattered rain showers are forecast to move eastward toward
central Missouri early Friday morning. These showers should move
toward the Mississippi River by midday but may weaken/dissipate
with time. The rain looks light, so visibility restrictions seem
unlikely at this time. Light easterly winds are forecast to veer
more to the southeast with time.

&&

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

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Gosselin