Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

991
FXUS63 KLSX 150356
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1056 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 /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1043 PM CDT Fri Aug 14 2026

Showers and thunderstorms will continue to move across northeast
Missouri and west central Illinois through 15Z on Saturday
morning. Have added a TEMPO group with IFR visibilities in heavy
rain between 06-10Z. These conditions may need to extended past
10Z. Elsewhere and past 15Z at UIN, mainly dry and VFR
conditions are expected. Winds are expected to be less than 10
knots outside of thunderstorms.

&&

.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.
     Flood Watch until 10 AM CDT Saturday for MOZ018-019-026-027.
     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.
     Flood Watch until 10 AM CDT Saturday for ILZ095-096.

&&

$$

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