Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

128
FXUS63 KLSX 141942 CCA
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
216 PM CDT Fri Aug 14 2026

.KEY MESSAGES...
- Dangerous heat and humidity will continue through Sunday for
  much of the area. The Extreme Heat Warning and Heat Advisory
  have both been extended through Sunday for most locations.

- There are shower and thunderstorm chances late tonight and
  tomorrow morning in NE MO and west-central IL (20-50%). More
  chances arrive on Sunday morning as a cold front sweeps
  through the area (20-40%).

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 244 AM CDT Fri Aug 14 2026

The central CONUS remains beneath an upper level ridge, with the
strongest westerlies well to the north and east of the Mid-
Mississippi Valley. The ridge will continue to amplify through
Saturday afternoon before it finally begins to flatten out on
Sunday as a shortwave ripples across the northern tier of the US
and southern Canada. The building ridge will keep very warm
temperatures in place through the depth of the troposhpere, with
dangerous heat and humidity in place at the surface. Like the
last few days, the only relief potential from the heat through
the weekend will be in the form of showers or thunderstorms.
Also like the last few days, these storms will largely be
confined to our north, closer to the stronger westerlies and
near the nose of the nocturnal low level jet over our northern CWA.

There is however an MCV currently slowly tracking across western IA.
This will likely initiate a round of storms this evening across
eastern IA, and these storms may push as far south as NE MO in the
late evening. Storms are expected to then further blossom in the
early morning hours as the low level jet ramps up, again focused in
our NE and further to our north. We`ll see a similar setup on
Saturday night/Sunday morning, with precipitation chances maximized
across our north. Both tonight and tomorrow night 0-6km shear will
be between 25-35kts, which could be enough to sustain a few strong
updrafts. The main hazard with any storms would be damaging winds or
heavy rain.

While precipitation will be focused toward our NE through Sunday
morning, it should be noted that these weakly forced
environments have notoriously low predictability. Features such as
remnant MCVs, outflow boundaries, and gravity waves are not reliably
resolved. These features could certainly be enough to initiate
showers or thunderstorms at times or locations other than what`s
mentioned above. That`s what happened this morning, when the low
level jet interacted with an outflow and gravity waves to push
convection across a large portion of the forecast area.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 244 AM CDT Fri Aug 14 2026

The forecast on Sunday is a bit more complicated due to the northern
tier shortwave mentioned above. This disturbance is expected to push
a weak cold front into the region on Sunday. This will not only
usher slightly cooler temperatures into the area, but also bring a
chance for afternoon showers and storms. At this time, it`s
uncertain just how far south the front will make it, but it appears
likely that it will be draped somewhere across the Mid-Mississippi
Valley, resulting in dramatically hotter conditions across our south
than our north. At this point, it appears more likely than not that
the vast majority of our area currently under a heat headline will
remain quite hot through Sunday, so I`ve extended the headlines out
through Sunday evening. The exception is some of our NE MO
counties, where it looks like the cold front may bring some
relief on Sunday.

A more noticeable change to the sensible weather for the vast
majority of the CWA will begin on Monday. First of all, most
guidance has Sunday`s cold front stalling out in the vicinity
of our southern CWA, so we should be starting the day a little
cooler than what we`ve seen lately. Additionally, the upper
level winds will become more northwesterly in response to a
stout shortwave diving across south-central Canada. Weak cold
air advection along these winds will help keep temperatures more
seasonal for this time of year. The above shortwave will also
bring a much stronger cold front through the region sometime on
Wednesday. The NBM is currently favoring a slower solution,
pushing temperatures back above normal on Wednesday. Both
frontal passages (Sunday and Wednesday) will also bring a chance
for showers and thunderstorms to the region, though at this
time, there is no strong evidence that the environment will be
supportive for strong to severe storms.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1239 PM CDT Fri Aug 14 2026

This morning`s convection has largely departed the area, and
winds are gradually swinging back around to the south behind an
associated outflow boundary. These southerly winds are expected
to persist into the evening before slackening tonight. Another
round of showers and thunderstorms are expected across portions
of northern MO and west-central IL late tonight and tomorrow
morning, though at this time, it appears that they will be
focused away from all TAF sites other than UIN. That said,
thunderstorm activity the last few mornings has been quite
difficult to predict, and I can`t rule out storms pushing
further to the south, like they did this morning. However, my
confidence in this happening is not nearly high enough to
include a mention of thunder in any of the other TAFs.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 9 PM CDT Sunday for MOZ035-036-042-052.
     Extreme Heat Warning until 9 PM CDT Sunday for MOZ041-047>051-
     059>065-072>075-084-085-099.
     Heat Advisory until 9 PM CDT Saturday for MOZ026-027-034.
IL...Heat Advisory until 9 PM CDT Sunday for ILZ058>060-064-065-
     097>099.
     Extreme Heat Warning until 9 PM CDT Sunday for ILZ069-070-074-
     079-100>102.

&&

$$

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