Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

319
FXUS63 KLSX 170426
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1126 PM CDT Sun Aug 16 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected late this
  afternoon and evening mainly along and south of I-70. A
  couple of storms will be capable of mainly damaging wind
  gusts.

- Rain chances return Tuesday night into Wednesday and then
  Wednesday night into Thursday.

- Seasonable temperatures are expected for a majority of the
  area through this week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 314 PM CDT Sun Aug 16 2026

An MCV can be seen on visible satellite imagery and in surface obs
moving across northern Missouri and southern Iowa this afternoon. A
cluster of thunderstorms associated with this MCV raced through
northeastern Missouri and west-central Illinois earlier today,
producing a cold pool and outflow boundary that is moving toward I-
70. The outflow is becoming increasingly diffuse in satellite
imagery, though broken cloud cover has kept the cold pool in place
and kept instability from rebuilding in this portion of the CWA.

A cold front is currently edging into northeastern Missouri and will
continue south-southeastward through this evening. As it does so, it
will encounter an air mass characterized by 3,000 J/kg of
MLCAPE along and south of I-70. Forcing from the front and
passing MCV will initiate scattered convection in this part of
the CWA starting around 5-6pm. Effective shear may be as high as
30-35 kts, allowing for organized multicell clusters capable of
damaging wind gusts. Much of this shear is going to be
associated with the MCV and behind the front, so the potential
for strong to severe storms will be confined to along the front;
therefore, right along the I-70 corridor. Additionally, LCLs
along the front may be low enough to allow for a threat of brief
tornadoes in bowing segments thanks to about 30 kts of 0-3km
shear.

Convection is expected to depart the CWA eastward shortly after
midnight, with the front clearing the area through the early
morning hours. A much more comfortable air mass will then settle
into the region, with highs tomorrow expected to only top out
in the low to mid 80s for most locations.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 314 PM CDT Sun Aug 16 2026

Portions of the CWA will only have a brief break from the heat, as
guidance consensus is that as Monday`s post-frontal air mass shifts
east, low-level ridging will nose into the region. However, there is
not a consensus as to how far north the crest of the ridge will
build, and therefore, how warm temperatures at the surface will get.
The overall trend over the last 24 hours has been for a less
aggressive ridge, with NBM probabilities for highs reaching and
exceeding 90 degrees are at most 50-70% over southeastern Missouri
Tuesday and south of I-70 on Wednesday.

Wednesday`s temperatures will have to contend with a cold front
dropping southward through the CWA. While guidance consensus is that
much of the CWA will not see FROPA prior to peak heating, associated
rainfall and cloud cover will produce an effective boundary further
south across the area. This will produce a strong temperature
gradient bisecting the CWA west to east, with low to mid 80s to the
north and low to mid 90s to the south. Once the front pushes south
of the area on Thursday, near normal to below normal temperatures
are expected through the weekend.

As the front slowly sinks through the area, guidance consensus is
that two shortwaves will ripple through the Midwest; one early
Wednesday, and one early Thursday. The location of the front during
the passage of the waves is where rainfall will be focused, and this
is currently north of I-70 Wednesday morning and south of I-70
Thursday morning. The front appears to be progressive enough to
mitigate a threat for flooding. However, ensemble guidance supports
PWAT of 1.5-2", and given upper-level flow parallel to the southward-
moving front, training convection capable of locally heavy rainfall
may be a concern.

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1118 PM CDT Sun Aug 16 2026

Scattered showers and thunderstorms will continue moving through
eastern Missouri and southern Illinois tonight. While the
strongest storms will likely be through our area into eastern
Illinois by 06-07Z, a few lingering weaker showers or storms
will likely continue to move across parts of south central
Illinois through 09-12Z. Thunderstorms will be capable of
reducing the visibility to 2SM or less in locally heavy
downpours. Wind gusts to 35-40kts will also be possible with the
strongest storms. There`s still a signal for MVFR stratus
across the eastern Ozarks into southern Illinois before sunrise.
Stratus may stretch as far north as the St. Louis Metro area,
and up to I-70 or I-55 in Illinois. With that in mind, the
signals aren`t particularly strong, so confidence in MVFR
ceilings isn`t high at this time. Any low clouds that do develop
should lift and scatter by 17-18Z with VFR flight conditions
prevailing thereafter.

&&

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

&&

$$

SHORT TERM...Elmore
LONG TERM...Elmore
AVIATION...Carney