Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

054
FXUS63 KLSX 160003
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
703 PM CDT Wed Apr 15 2026

.KEY MESSAGES...

- Showers and thunderstorms are expected through tonight, with a threat
  of strong to severe thunderstorms capable mainly of damaging
  winds and large hail through 11pm.

- Showers and thunderstorms, some strong to severe, are expected
  again on Friday.


&&

.SHORT TERM... (Through Late Friday Night)
Issued at 159 PM CDT Wed Apr 15 2026

A series of shortwaves can be seen across the Great Plains in water
vapor imagery, with southwesterly flow across the Middle Mississippi
Valley ahead of these waves. An elongated fetch of warm, moist air
is feeding into the region from the Gulf, aiding in forcing
scattered showers and thunderstorms now across southeastern Missouri
and southwestern Illinois. Model and ACARS soundings out of KSTL
suggest that this convection is elevated above an inversion at 800-
850 mb. Associated convective debris has been inhibiting surface
heating so far, causing a dearth of instability along and south of
the MO I-44/IL I-55 corridor this afternoon. Westward across western
Missouri, insolation and mid-60s to low 70s dewpoints have yielded
upwards of 2000 J/kg of MLCAPE per recent SPC mesoanalysis. Here, an
extensive area of cumulus can be seen in visible satellite imagery.

Subtle leading waves within the southwesterly flow and an area of
lift via jet dynamics will produce nebulous lift across portions of
central and northeastern Missouri, as well as west-central Illinois
through this afternoon into this evening. If enough surface heating
is realized, then the cap will break, allowing for scattered showers
and thunderstorms among the aforementioned instability and about 50
kts of effective shear. This is an environment favorable for
organized updrafts, with some supercell structures possible. A
limiting factor for robust supercells is slight veer-back-veer
vertical wind profiles and/or weak low to mid-level flow noted in
ACARS soundings and the KLSX VWP. A mostly straight hodograph with
these attributes will lead to both left and right-moving updrafts
that will tend to be shorter-lived as they interact and grow into
localized clusters. If this round materializes, large hail and
damaging wind gusts will be the primary threats, though about 20 kts
of 0-1km shear and 200m2/s2 of low-level SRH means that there is a
low chance for brief tornadoes.

A solution that CAMs are increasingly supporting is that convection
this afternoon and early evening remains mostly subdued, allowing
for the atmosphere to remain undisturbed ahead of a cold front
moving into the region this evening and the early overnight hours.
Then, lift from the shortwave and upper-level jet will be greater,
pairing with the cold front to force numerous updrafts along and
immediately ahead of the front as it moves eastward. Initially, both
the vertical wind and thermal profile will be similar as this
afternoon, leading to discrete supercells. Confidence is high that
these discrete storms will form west of the CWA, growing upscale
into clusters and line segments as they interact with each other and
the front thanks to deep layer shear vectors parallel to the
boundary. These interactions and waning instability after sunset
will lead to a weakening trend as the line segments move into the
CWA. The primary threat with this round will be damaging wind gusts,
with line segments surging northeastward carrying a tornado threat
thanks to 30-40kts of 0-3km shear vectors oriented southwest to
northeast.

Once the convection and associated stratiform rain clears the CWA
during the early morning hours, mainly dry conditions are expected
through early Friday. Though, there is a low chance for convection
across southeastern Missouri and southwestern Illinois tomorrow
afternoon.

Our attention then turns to Friday as a highly-amplified trough
ejects out into the Plains and sends a cold front into the Midwest.
Ahead of this front, ensemble clusters have a median value of 2,000
J/kg of SBCAPE, with deterministic models showing as much as 3-4,000
J/kg. Deep layer shear is progged to be 45-50 kts, creating a
environment conducive for strong to severe thunderstorms across much
of the Midwest. Given the lead time and forecast load prior to then,
further details on thunderstorm threats, timing, and placement for
Friday will wait until later updates.

Elmore

&&

.LONG TERM... (Saturday through Next Wednesday)
Issued at 159 PM CDT Wed Apr 15 2026

At daybreak Saturday morning, guidance consensus is that Friday`s
front will be deep into the Ohio Valley and clear of the CWA as the
axis of the upper-level trough pivots eastward toward the Middle
Mississippi Valley. With the core of this trough and the track of
the associated surface low being well north-northeast of the region,
the CWA will miss out on the core of the post-frontal airmass.
Still, increasingly deep northwesterly flow will push cooler air
into the CWA, pushing Saturday and Sunday`s temperatures to at and
just below climatological normals.

The trough will quickly shift eastward early next week, allowing for
low to mid-level ridging to build and southwesterly flow to return
across the region. This favors warming temperatures, with ensembles
clustering around seasonal normals starting Monday and then above
normal by mid-week.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 702 PM CDT Wed Apr 15 2026

A cold front is moving eastward, entering western MO, with a south-
southwest to north-northeast oriented broken line of strong to
severe storms along and ahead of the approaching boundary. These
storms are forecast to near the central Missouri terminals at the
start of the TAF, followed by KUIN and then the STL metro terminals
later this evening/early tonight. Any thunderstorms that directly
impacts terminals will be capable of IFR visibilities, gusty and
variable winds, along with heavy rain and frequent lightning.
Scattered showers may linger behind convection with conditions
expected to improve by late tonight for all terminals. Surface winds
veer southwesterly behind the front overnight becoming increasingly
southerly by Thursday afternoon.

Peine

&&

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

$$

WFO LSX