Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

592
FXUS63 KLSX 150956
AFDLSX

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

.KEY MESSAGES...

- Multiple opportunities for showers and thunderstorms will exist
  Tuesday through Thursday, with the highest chances Wednesday
  evening. Some thunderstorms could be severe Wednesday afternoon
  and evening.

- Temperatures will vary from near to slightly below average with
  the exception of above average temperatures on Wednesday.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 338 AM CDT Mon Jun 15 2026

Light to calm winds at the eastern flank of a surface high pressure
center is promoting efficient radiational cooling in between bands
of upper/mid-level clouds associated with a passing shortwave
trough. As a result, temperatures are falling into 50s F this
morning, suggesting that development of patchy river valley fog is
possible along the Missouri River and the Ozarks with crossover
temperatures being reached and around 20 F water-air temperature
differences. Strong insolation and increasingly westerly low-level
flow and WAA to the north of the migrating high pressure center will
result in slightly warmer temperatures from Sunday in the mid-70s to
near 80 F. With flow continuing to back to southerly tonight, low
temperatures will generally be warmer but still largely in the 50s F.

On Tuesday, an upper-level shortwave trough within northwesterly
flow will traverse the Midwest and Great Lakes, forcing a cold front
southeastward through the CWA. A broken band of showers and a weak
thunderstorm or two are expected to precede the front during the
morning and afternoon within a narrow ribbon of low/mid-level moist
isentropic ascent. Limit moisture return and weak convergence will
limit development of showers and thunderstorms along the front
itself. Despite any of this development being "surface-based",
severe weather is unlikely due to HREF probabilities of 1000+ J/kg
SBCAPE 30 percent or less and low equilibrium levels favoring only
low-topped convection. High temperatures on Tuesday are forecast to
be a couple degrees warmer into the low-80s F ahead of ront`s early
afternoon position (near I-44 in MO, I-70 in IL).

Pfahler

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 338 AM CDT Mon Jun 15 2026

The aforementioned cold front will stall somewhere near the MO-AR
border late Tuesday evening before beginning to lift back
northeastward as a warm front overnight into Wednesday morning in
response to gradual surface cyclogenesis across the Northern
Plains/Upper Midwest ahead of the next upper-level shortwave trough
and the formation a strong (50 kt) southwesterly LLJ. Model guidance
varies on how much and when shower and thunderstorm development will
occur through Wednesday morning with discrepancies on how quickly
sufficient moisture arrives. With a LLJ and associated WAA and
moisture transport of this strength, it seems likely that at least
scattered development will occur at the LLJ nose across IA, perhaps
northeastern MO with a threat of marginally severe hail. However, if
upscale growth into an MCS can occur, Corfidi upshear vectors would
favor southeastward propagation along the warm front along/east of
the Mississippi River near the CWA.

Model guidance is coming into better agreement on a surface low
track near the IA-MN border into southern WI during the day
Wednesday, favoring the warm front lifting to the northeast of the
CWA by afternoon and a cold front arriving from the northwest
sometime during the evening. Anomalous mid and low-level flow
leading to 45 to 55 kt of deep-layer wind shear will be more than
sufficient for organized severe thunderstorms, combined with
increasing moisture and most deterministic guidance indicating 1500+
J/kg of MLCAPE. This parameter space, including a deep layer of
hodograph curvature, is favorable for supercells, but potential cold
pool development (1000+ J/kg DCAPE) and approximately 45 deg
orientation of the cold front with deep-layer wind shear suggests
that thunderstorms could congeal into an MCS/QLCS or mixed more of
supercells and line segments. Therefore, all severe hazards are
reasonable threats on Wednesday. Currently, the most likely
locations of thunderstorm initiation during the afternoon and
evening are across IL near the warm front and northern MO along the
cold front with a capping inversion evident in forecast soundings
across the open warm sector. However, if more widespread morning
showers and thunderstorms/MCS linger(s) well through midday, a
remnant outflow boundary could also be a focus closer to the CWA.
Conversely, such activity might limit how much instability recovers
subsequently. All things considered, there is still quite a bit of
uncertainty on the Wednesday`s severe threat and there appears to be
a conditionality to at least a higher end or widespread severe
weather event impacting the CWA. Thunderstorms will tend to weaken
Wednesday night as instability decreases after sunset and they
progress southeastward into decreasing wind shear.

Aside from thunderstorms, Wednesday is anticipated to be the warmest
day of the week with 850-hPa temperatures reaching the 90th
climatological percentile and potential downslope warming of
southwesterly flow off the Ozark Plateau. Considering that morning
showers and thunderstorms along with cloud cover may impact
temperatures, NBM interquartile high temperature ranges are around 5
F, ranging from the low-80s to low-90s F across the CWA, warmest in
the lee of the Ozarks.

On Thursday, the majority of model guidance has the cold front
either across southeastern MO or south of the CWA altogether,
leading to largely elevated showers and a few thunderstorms at times
along/south of I-70 until the front continues further southward.
Behind the front, slightly below to near average temperatures are
expected into the weekend along with dry conditions Friday into
Saturday with some degree of upper-level shortwave ridging and a
passing surface high pressure center. However, global model guidance
indicate a transition to upper-level quasi-zonal flow Sunday into
early next week with opportunities for showers and thunderstorms
returning.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 455 AM CDT Mon Jun 15 2026

Aside from patchy river valley fog potentially impacting KSUS
through 12z, dry and VFR flight conditions will persist through
tonight. The chance of showers, possibly a thunderstorm increases
Tuesday morning into afternoon, but impacts are uncertain,
especially before the end of the valid TAF period.

Pfahler

&&

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

$$

WFO LSX