Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

590
FXUS63 KLSX 160820
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
320 AM CDT Tue Jun 16 2026

.KEY MESSAGES...

- There is a chance of showers and thunderstorms at times today
  through Thursday.

- Some thunderstorms Wednesday afternoon and evening could be
  severe with damaging winds, large hail, and a few tornadoes,
  followed by a low threat of locally heavy rainfall overnight.

- Warm and windy conditions are also expected on Wednesday with
  occasional gusts of 40 to 45 mph outside of thunderstorms.


&&

.SHORT TERM...  (Through Late Wednesday Morning)
Issued at 319 AM CDT Tue Jun 16 2026

An upper-level shortwave within northwesterly flow will continue to
track southeastward through the Midwest and Great Lakes today. An
associated cold front will press southeastward through the CWA this
morning into afternoon, forcing a band of scattered showers,
possibly a few thunderstorms, mainly along a narrow corridor of
weak, prefrontal low to mid-level moist isentropic ascent. Shower
and thunderstorm development along the front itself during the
afternoon and evening is uncertain due to a combination of
seasonably modest moisture return (dewpoints around 60 F) and weak
frontal convergence, although locally strongest in south-
central/southwestern IL. DCAPE of 750 to 1000 J/kg and inverted V
signatures in forecast soundings suggest a threat of gusty winds
with any stronger thunderstorm, but their expected low-topped nature
(low equilibrium levels), 500 to 750 J/kg of MLCAPE, and potential
updraft dry air entrainment (strong wind shear with very dry mid
levels) all lead to low confidence in any severe thunderstorms. High
temperatures will be in the mid-70s to low-80s F, coolest in
northeastern MO/west-central IL which experience FROPA earlier in
the day.

The aforementioned cold front will stall somewhere near southeastern
MO late this evening before lifting back northeastward as a warm
front later tonight through Wednesday morning in response to surface
cyclogenesis in the Northern Plains, ahead of the next shortwave
trough, and intensification of a strong, 50+ kt southwesterly LLJ.
In response to strong WAA and moisture transport, initiation of
showers and thunderstorms is expected to eventually occur Wednesday
morning. CAMs still vary on exactly when and where this development
will take place but the location of the LLJ`s nose points to central
or eastern IA, possibly as far south as northeastern MO/west-central
IL with a conditional threat of large hail from elevated supercells.
Upscale growth into an MCS seems likely through the morning with
Corfidi upshear vectors indicating propagation southeastward, as far
southwest as west-central/south-central IL. However, the vast
majority of CAMs keep this MCS out of the CWA, across central and
northern IL. Therefore, morning thunderstorms are not anticipated to
have a significant impact on subsequent instability later in the
day.

Pfahler

&&

.LONG TERM...  (Wednesday Afternoon through Monday)
Issued at 319 AM CDT Tue Jun 16 2026

The warm front will quickly lift northeast of the CWA by the
afternoon, but a cold front trailing an elongated area of low
pressure in the Upper Mississippi River Valley will reach the CWA
during mid-afternoon. The presence of a capping inversion across the
open warm sector suggests that initiation will be largely confined
to these fronts, with initiation along the cold front expected to
take place in the 2 to 4 pm timeframe. Anomalously strong low and
mid-level flow with 45 to 55 kt of deep-layer wind shear combined
with 1500+ J/kg of MLCAPE will be more more than sufficient for
organized severe thunderstorms including supercells. After
initiation, storm mode becomes much less clear considering that
large-scale forcing will not be particularly strong this far
southwest and deep-layer wind shear-front orientation will be
anywhere from 45 to 60 deg. Therefore, a mixed mode of supercells
and line segments are possible with time. All severe hazards appear
likely including damaging winds, large hail, and a few tornadoes,
although storm mode will modulate which hazard is dominant. A strong
tornado (EF2+) is possible as well, with the most favored location
in the CWA being across west-central IL where the highest SRH is
forecast. However, SRH increases along the entire cold front after
sunset as the LLJ intensifies which may lead to a window of greater
tornado potential (assuming destructive storm interactions do not
dominate) before CINH begins to increase, instability decreases, and
convergence along the front also decreases. Overall, the greatest
severe threat will be along/north of I-44 in MO and I-70 in IL with
the tornado threat maximized in west-central IL.

Overnight, confidence decreases in severe weather, but the threat of
locally heavy rainfall increases as the cold front slows and
increases the potential for thunderstorms to train in some locations
south of I-70 in an environment with PW exceeding the 90th
climatological percentile and deep warm cloud depths.

Outside of thunderstorms, strong gusty southwesterly winds of 40 to
45 mph are expected at times through the late Wednesday morning into
afternoon with BL mixing favoring some momentum transfer of the 50+
kt LLJ to the surface. A Wind Advisory could be needed if confidence
increases in deeper mixing and 45+ mph gusts. Additionally,
Wednesday will be the warmest day of the week with 850-hPa
temperatures reaching the 90th climatological percentile along with
some potential downslope warming off the Ozark Plateau, leading to
high temperatures in the mid-80s to low-90s F.

On Thursday, the cold front is expected to slowly depart the CWA,
but showers and thunderstorms are still expected along the front and
on the cool side of the front mainly south of I-70 through the day
with lingering elevated instability and some component of mid-level
flow overrunning the front. With the cooler post-frontal airmass,
and in Thursday`s case cloud cover, seasonably cool temperatures are
forecast Thursday and Friday.

Over the weekend, global model guidance continue to advertise upper-
level quasi-zonal flow becoming established with several shortwave
troughs or perturbations navigating the flow, providing
opportunities for showers and thunderstorms at times late Saturday
into early next week. However, these flow patterns are notorious for
low predictability, which significantly decreases confidence in any
details at this juncture.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1034 PM CDT Mon Jun 15 2026

Dry and VFR conditions will prevail through the night before a
cold front brings a threat for showers and thunderstorms to all
TAF sites through the day tomorrow. The cold front, currently
advancing south from northwest Iowa, will be fairly weak and
moisture-starved by the time it arrives in the Mid-Mississippi
Valley. Despite this, sufficient low-level moisture will exist to
threaten at least scattered showers and a few rumbles of thunder
through the morning at KUIN, the late morning in central Missouri,
and early afternoon in St. Louis. Aside from the typical hazards
associated with thunderstorms (lightning, heavy rain), a low
(5-10%) chance for wind gusts to 40-50kts exists primarily in the
St. Louis metro area. Outside of thunderstorms, expect 15-20kt
gusts ahead of and directly behind the front.

Activity threatening the regional terminals will likely abate by
sunset, though another threat for convection will exist for
Wednesday.

MRB

&&

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

$$

WFO LSX