Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

316
FXUS63 KLSX 191038
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
538 AM CDT Sat Sep 19 2026

.KEY MESSAGES...

- Summer-like heat continues today with relief from a cold front
  starting Sunday.

- More widespread showers and thunderstorms are expected Sunday
  night into Monday.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 343 AM CDT Sat Sep 19 2026

An upper level ridge continues to reside over the central CONUS,
which has been the driver behind the heat and humidity lately.
The front that brought some subtle heat relief to northern areas
and spotty showers and thunderstorms has retreated north,
allowing the hot and humid air mass to return over the entire
forecast area today. Ensemble guidance indicates that 850mb
temperatures are 21-22 degrees C (>95th percentile of
climatology) translating to mid to upper 90s surface
temperatures in full mixing. With deeper mixing, dewpoints are
expected to be lower in the mid to upper 60s leading to lower
heat index values around 100 across the region. An upper level
tough that is currently over the western CONUS will move to the
east through the day today and into Sunday, eventually pushing a
cold front into our area beginning Sunday. Temperatures on
Sunday will still be hot and humid south of the front as it
begins to push through the region. This will lower high
temperatures into the 80s in northern MO, while southeastern MO
will remain in the 90s. However, modest humidity will prevent
more widespread 100+ heat index values. As a result no changes
are being made to the Heat Advisory as it aligns well with the
forecast.

The low-level jet is expected to develop some showers and
thunderstorms in eastern KS overnight tonight, but are expected
to significantly weaken by the time they reach central MO. HREF
guidance shows that there is about a 10-40% chance that some
convective remnants could translate through northeastern MO.
Otherwise, today and Sunday are looking to remain dry.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 343 AM CDT Sat Sep 19 2026

The light at the end of this hot tunnel is in sight. Cluster
analysis continues to show uncertainty on the speed of the front
with much cooler temperatures behind it. The relief will begin
in northern MO on Sunday during the day and is expected to be
completely through the area by Tuesday. Current NBM guidance
interquartile range for the high temperatures on Monday reaches
10 degrees due to the uncertainty in the fronts exact position
and speed. Behind the front temperatures are expected to be much
cooler, and latest NBM guidance continues to trend cooler than
previous days. For example, NBM has dropped Tuesday max
temperature forecasts around 8 degrees over the last 48 hours,
now with highs only in the upper 60s to low 70s. This air mass
will dominate for the rest of the week with a gradual warming
through the 70s.

The highest chance for showers and thunderstorms in the next
week will be Sunday night into Monday morning behind the cold
front. While the confidence is low on the exact timing and
location of this convection, there is a 60-80% chance across the
region of measurable rainfall during this period, and 30-60%
chance of seeing 0.25 inches of rain.

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 538 AM CDT Sat Sep 19 2026

Dry and VFR conditions are expected through the TAF period. A
slow moving cold front is expected to start moving into the area
from the north toward the end of the TAF period that will start
to shift the winds in a more northward direction.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 8 PM CDT this evening for MOZ047>049-
     059>065-072>075-084-085-099.
IL...Heat Advisory until 8 PM CDT this evening for ILZ064-069-070-
     074-079-100>102.

&&

$$

SHORT TERM...Asel/Kimble
LONG TERM...Asel/Kimble
AVIATION...Asel/Kimble