Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

390
FXUS63 KLSX 152321
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
621 PM CDT Mon Jun 15 2026

.KEY MESSAGES...

- Strong to marginally-severe thunderstorms exists tomorrow along
  and south of I-70 in Missouri and Illinois, with isolated
  instances of damaging wind being the main threat.

- A more noteworthy chance for severe weather exists across much
  of the region Wednesday afternoon. The strongest thunderstorms
  would threaten damaging wind and brief tornadoes, along with
  locally-heavy rain.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 336 PM CDT Mon Jun 15 2026

After another pleasant day today, a weak cold front is on tap to
bring a round of scattered showers and possibly a few thunderstorms
during the day tomorrow. This doesn`t pose nearly as great a threat
as Wednesday`s front, and the latter will be discussed in more
detail in the long term portion of the discussion. Before we get to
all of that, downright fantastic weather is in place throughout the
mid-Mississippi River valley, thanks to mild northwest flow and
seasonably low dewpoints in the upper 40s to low 50s. While
afternoon heating has been enough to generate a deck of scattered
fairweather cumulus across the southern half of Missouri and much of
Illinois, dry conditions are expected to persist the rest of the
day. Overnight, northwest winds will back to the southwest and
become nearly calm, and nearly clear skies will allow for efficient
radiative cooling conditions. We may also see some shallow, patchy
fog in Ozark river valley bottoms, but relatively low humidity will
prevent this in most other areas.

During the day tomorrow, a shortwave will round the base of the
synoptic trough across the Great Lakes and eastern Canada,
driving a weak cold front into the area between early morning and
early afternoon. Ahead of it, increasing southwesterlies will
produce modest moisture advection, and the linear forcing along
the front is expected to squeeze out some scattered showers,
possibly a few thunderstorms. Due to the limited moisture content
(1-1.25 inch PWAT) and scattered coverage, rain amounts are
expected to be limited and many areas are also expected to miss
out entirely. The potential for strong or severe storms is also
limited, but there is just enough instability (500-1000 k/kg) and
wind shear (30-40kt) to support organized updrafts during the
afternoon, particularly from I- 70 southward. Isolated damaging
wind gusts and quarter-sized hail would be the primary threats if
we do see a few stronger cells. While some showers may move into
the area in the morning, stronger cells should be limited to the
afternoon (roughly 1-8pm) and weaken near and after sunset.

BRC

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 336 PM CDT Mon Jun 15 2026

By Wednesday morning, a much stronger shortwave/deeper surface low
and jet streak will move through the Midwest and Great Lakes just to
our north. This will initially drive much more robust northward
moisture return into our area during the day Wednesday, followed by
a stronger cold front Wednesday evening and overnight. Before the
cold front arrives, the warm sector airmass is expected to quickly
destabilize thanks to abundant sunshine, increasingly rich low level
moisture (upper 60s / low 70s dewpoints), and steepening mid-level
lapse rates. While subsidence aloft may cut into CAPE projections
just a bit, values between 1000-2000 J/kg of SBCAPE appear rather
likely by mid/late afternoon. Meanwhile, seasonably strong westerly
mid-level flow is also projected to produce ample deep layer shear,
with between 50-60kt currently forecast along and ahead of the
front. Given the above, the bulk parameter space is more than
supportive of strong/severe thunderstorms as the front overturns
this airmass.

The finer scale details are more difficult to determine, and this is
mainly linked to uncertainty in the progression/orientation of the
front and the strength of a capping inversion. Early indications
suggest that as the front moves south and becomes oriented more east
to west, linear storm modes will be favored overall, but exactly how
long this takes to materialize is uncertain at this time range. We
do note some clockwise turning in hodographs initially, so storms
may start off as supercells before being overtaken by the front,
especially if a capping inversion can keep initial updrafts more
isolated. Mid-level lapse rates will also support the potential for
large hail, but this threat will gradually wane if/when storms
become primarily linear. Tornadoes appear possible given the bulk
shear parameters and sufficiently low LCLs, although this threat
will also be tied to how quickly storms transition from supercells
to a linear complex, and is a lower overall threat. Overall,
damaging winds appear most likely of these hazards, with steep low
level lapse rates and relatively high confidence that storms will
eventually become linear. Locally heavy rainfall will also be
possible, due to increasingly rich moisture (PWAT of 1.7-1.9 inches)
and storm motions that become more parallel to the advancing cold
front with time. Storm hazards appear to be maximized across
northeast Missouri and west-central Illinois, with lower
confidence further and further south and later into the night.

Thursday morning the advancing front is expected to slow and
potentially stall across the Ozarks, maintaining additional chances
for showers and thunderstorms through the day. Confidence is very
low regarding this potential at this time, as this will be linked to
how overnight storms and their resulting cold pool impact the
environment. Dry conditions are expected to end the work week
Friday.

Beyond Friday, model guidance has increased probabilities for
more showers and thunderstorms late in the weekend, with a rather
strong ensemble signal for widespread precipitation at some point
between late Saturday and early Monday. Confidence in the
specifics remains low, but there is a robust signal for
anomalously high moisture content (PWAT ensemble means near the
95th percentile) and a relatively high number of ensemble members
forecast heavy rain in our area at that time range. Timing and
location details will need to be ironed out, as there are
considerable QPF differences between the various ensemble clusters
at that time range linked to differences in timing/strength of a
passing shortwave.

BRC

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 552 PM CDT Mon Jun 15 2026

Dry and VFR conditions will prevail through tonight ahead of a
cold front that passes through the Mid-Mississippi Valley
tomorrow. Very little moisture will be available to this weak
front as it crosses from northwest to southeast, leading to
scattered coverage of any showers or shallow thunderstorms. The
threat should not last very long at any one location, abating by
sundown at the TAF site. The main threat for the strongest storms
would be wind gusts to 40kts, but nearly all of the convection
would remain much weaker than this.

Outside of the thunderstorms, gusty winds to 20kts can be expected
ahead of and directly behind the front. With the loss of daytime
heating and passing of the front itself, expect the winds to
weaken near sunset as well.

MRB

&&

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

$$

WFO LSX