Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

494
FXUS63 KLSX 170821
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
321 AM CDT Wed Jun 17 2026

.KEY MESSAGES...

- Strong to severe thunderstorms are forecast from mid-afternoon
  through late evening, particularly north of I-70. Damaging winds
  will be the most common severe hazard, but large hail and a few
  tornadoes are also possible.


- Southwesterly winds will occasionally gust 40 to 50 mph across
  much of the area late this morning into evening outside of
  thunderstorms.

- Showers and a few thunderstorms will linger into Thursday with
  another opportunity for showers and thunderstorms late Saturday
  through early Monday, bookending dry conditions.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 320 AM CDT Wed Jun 17 2026

Monday`s cold front has stalled near the I-70 corridor, but will
begin to lift northeastward as a warm front through sunrise in
response to surface cyclogenesis across the Northern Plains with an
approaching upper-level shortwave trough. A strong, 50+ kt
southwesterly LLJ will veer toward the Upper and Mid-Mississippi
River Valley with increasing showers and thunderstorms expected
across IA near its nose through sunrise among strong WAA and
moisture transport. Most CAMs bring the southwestern edge of these
showers and thunderstorms southeastward into portions of
northeastern MO, west-central and south-central IL through the
morning, which could pose a marginal hail threat with the potential
for a couple of embedded supercells within a larger cluster of
thunderstorms.

Through midday or early afternoon, these showers and thunderstorms
should migrate to the east of the CWA, with quick moderation and
northeastward lifting of any remnant outflow or cold pool out of the
CWA given synoptic-scale maintenance of the strong southwesterly
LLJ. Increasing insolation, favorable southwesterly flow, and some
downslope warming off the Ozark Plateau will support high
temperatures in the upper 80s to low-90s F for most of the CWA.
Given BL mixing facilitating downward momentum transfer from the LLJ
to the surface, occasional wind gusts of 40 to 50 mph are forecast
from late morning through late afternoon, warranting expansion of
the Wind Advisory for all of the CWA aside from a portion of
southeastern MO.

With a capping inversion across the portion of the warm sector
across the CWA, initiation of thunderstorms is not expected until a
cold front enters northeastern MO and west-central IL sometime in
the 2 to 4 pm timeframe this afternoon. Anomalously strong flow at
lower and mid-levels will lead to 45 to 55 kt deep-layer wind shear
which, combined with 1500 to 3000 J/kg MLCAPE, will be favorable for
organized severe thunderstorms including supercells. With 45 to 60
deg orientation of deep-layer wind shear with the front, there is a
slight favoring of supercells remaining the dominant storm mode,
which is support by nearly all CAMs, leading to thunderstorms
capable of all severe hazards. With 1000+ J/kg of DCAPE, inverted V
signatures in forecast soundings, and 50+ kt winds not far above the
surface it will not be difficult for thunderstorms to produce
damaging winds, leading to that being the most common hazard. The
greatest tornado risk, including the potential for a strong tornado
(EF2+), will be across west-central and south-central IL (moreso in
central IL) where the largest low-level hodograph curvature exists
and LCLs will be lower. Further south along the cold front, high
LCLs from deeper BL mixing throughout the day will potentially be
less favorable for tornadogenesis along with some concern for
deconstructive storm interactions. There could be a brief window
that is more favorable just around/after sunset when LCLs lower and
the LLJ nocturnally strengthens, further elongating hodographs, but
frontal convergence and forcing altogether will be
decreasing/departing around that time.

The threat of severe weather will decrease late in the evening, but
there is a low threat of locally heavy rainfall with some training
of thunderstorms possible as the front slows south of I-70
overnight. However, fast storm motions will otherwise limit the
residence time/duration of any efficient rainfall (90th+ climo
percentile PW and deep warm cloud depths).

The cold front is progged to finally advance south of the CWA on
Thursday morning, but another wave of scattered showers and
thunderstorms are anticipated on the cool side of the front
along/south I-70 on Thursday as weak mid-level isentropic ascent
overruns the front and FGEN ebbs and flows. However, elevated
instability, and thus thunderstorms, will be mainly confined to
southeastern MO/southwestern IL. The post-frontal airmass and waves
of more abundant cloud cover will result in much cooler high
temperatures on Thursday, largely in the mid-70s to low-80s F.

Pfahler

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 320 AM CDT Wed Jun 17 2026

With gradual mid-level height rises and a weak surface high pressure
center in the Mid-Mississippi River Valley, seasonably cool
temperatures will persist through Friday along with dry conditions.
However, model guidance signals upper-level northwesterly flow
transitioning to quasi-zonal over the weekend, with at least one
more prominent shortwave trough passing between sometime late
Saturday and early Monday accompanied by another opportunity for
showers and thunderstorms. There are some indications for at least a
low threat of heavy rainfall Saturday night through Sunday night
with PW projected to be near the 95th climatological percentile and
a slow moving front in the region. The threat of strong/severe
thunderstorms will also need to be monitored on Sunday as well, but
potential morning showers and thunderstorms and the overall
variability and inconsistency precludes of model guidance precludes
the resolution of any details and leads to low confidence in either
threat at this point.

Early next week, there is a general consensus that upper-level flow
will become more northwesterly and greatest support in ensemble
membership for a wavering front to shift south of the CWA. These
ingredients support another period of seasonably cool and largely
dry conditions.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1002 PM CDT Tue Jun 16 2026

Light and variable surface winds have settled into the region and
are forecast to stick around until increased low/mid-level flow
increases from west to east near sunrise. This includes an unusually
strong 850mb low-level jet (50+kts) for June that will move into
central/northeast MO around 12z tomorrow. There is the potential for
a brief period of LLWS at KCOU/KJEF/KUIN around 10-12z as this low-
level jet moves in. However, the threat window for this looks to be
only 1-2 hours as surface winds quickly pick up with daytime mixing.
Surface winds will be very strong tomorrow with south-southwest
winds sustained 15-25kts with gusts to 30-40kts. There remains a low
chance (30-40%) for an early morning round of convection to slide
southeast across southern Iowa into central IL, potentially
impacting KUIN after 12z. Additional convection is forecast to
develop along a cold front tomorrow afternoon near northeast MO with
eventual southeastward progression of convection along with the
front. To cover this threat, PROB30 had been included as confidence
remains lower on how widespread the coverage of thunderstorms will
be along the cold front. The main threat expected with any strong to
severe thunderstorms will be damaging wind gusts, with a lesser
threat for tornadoes and large hail. Surface winds will fade after
sunset tomorrow remaining westerly for the remainder of this TAF.

Peine

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory from 1 PM this afternoon to 8 PM CDT this evening
     for Franklin MO-Gasconade MO-Jefferson MO-Lincoln MO-
     Madison MO-Saint Charles MO-Saint Francois MO-Saint Louis
     City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO.

     Wind Advisory from 10 AM this morning to 6 PM CDT this evening
     for Audrain MO-Boone MO-Callaway MO-Cole MO-Knox MO-Lewis
     MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-
     Pike MO-Ralls MO-Shelby MO.

IL...Wind Advisory from 1 PM this afternoon to 8 PM CDT this evening
     for Bond IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-
     Montgomery IL-Randolph IL-Saint Clair IL-Washington IL.

     Wind Advisory from 10 AM this morning to 6 PM CDT this evening
     for Adams IL-Brown IL-Pike IL.

&&

$$

WFO LSX