Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

619
FXUS63 KLSX 082338
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
638 PM CDT Mon Jun 8 2026

.KEY MESSAGES...

- The chance of showers and thunderstorms will lower this
  evening, but continue into Tuesday. A conditional threat of
  locally heavy rainfall and additional flash flooding exists into
  Tuesday morning.

- A thunderstorm or two could produce damaging winds and/or a
  tornado in far southeastern MO and southwestern IL this evening.

- High temperatures will reach the 90s F in some areas Tuesday
  through Thursday. With the highest humidity expected on Tuesday,
  confidence has increased in 105+ F heat index values along/south
  of the Missouri River during the afternoon/evening.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 323 PM CDT Mon Jun 8 2026

An upper-level low is nearly overhead of the CWA early this
afternoon, which continues to support downstream showers and
thunderstorms across northeastern MO, west-central/south-central IL.
However, a remnant MCV across southeastern MO is forecast to rotate
cyclonically northeastward around the parent low into southwestern
IL through late afternoon and evening. As destabilization continues
and this feature encounters the more unstable downstream airmass,
additional development of showers and thunderstorms is expected
along/east of the Mississippi River. This MCV, combined with a 30-kt
mid-level jet streak approaching on its heels, will act to increase
deep-layer wind shear at least marginally supportive of organized
thunderstorms (transient supercells and/or bowing segments) with a
threat of isolated damaging winds and a low tornado threat with some
low-level hodograph curvature. The amount of instability available
will be important dictating the severe weather threat, but recent
scattering/thinning of cloud cover, increasing cumulus, and SPC
Mesoanalysis depicting up to 1500 J/kg MLCAPE (including 100+ J/kg 0-
3 km). The most favorable area for severe weather will be
along/southeast of the Mississippi River and I-70 through the
evening.

Behind the upper-level low, mid-level height rises will ensue, which
will become generally unfavorable for much additional showers and
thunderstorms. However, the presence of a lingering remnant
convergent boundary trailing the MCV and a strengthening, modest LLJ
in addition to a potential upstream MCS developing across KS and
tracking eastward late tonight all leads to a continued chance of
showers and thunderstorms. With precipitable water decreasing, but
remaining above the 90th climatological percentile and deep warm
cloud depths along with vertical wind shear profiles indicating the
potential for training and backbuilding thunderstorms; there is a
conditional threat of locally heavy rainfall through Tuesday
morning. Considering that there are areas of moistened soils from
earlier heavy rainfall lowering flash flood guidance, much of the
Flood Watch has been extended through Tuesday morning. As for the
potential late night/early Tuesday morning MCS, CAMs all point to it
weakening by the time as it reaches central MO as it encounters
weaker deep-layer wind shear and increasing CINH. That being said,
gusty winds will still be possible if it is a mature, quickly
forward-propagating MCS.

On Tuesday, there could be at least early day showers and cloud
cover tracking eastward from what remains of the MCS, but it is
uncertain if there will be much, if any, redevelopment of showers
and thunderstorms through the remainder of the day as an upper-level
ridge axis shifts overhead. These factors introduce some question to
the exact high temperatures on Tuesday, varying from the mid-80s to
low-90s F. If clouds clear earlier and dry conditions prevail, 850-
hPa temperatures around 20 to 22 C suggest even warmer high
temperatures are in the realm of possibility. HREF probabilities of
105+ F heat index values are highest near and south of the Missouri
River with dewpoints projected to be well into the 70s F. In
response, a Heat Advisory has been issued for Tuesday afternoon and
evening in those areas.

Pfahler

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 323 PM CDT Mon Jun 8 2026

Global model guidance continues to indicate the upper-level
troughing across the Northern Plains will begin to weaken and shunt
the ridge eastward, with a cold front slowly approaching the CWA on
Wednesday and making a passage sometime Thursday. On Wednesday, low-
level flow will become more southwesterly and strengthen, allowing
for many locations to see high temperatures further into the 90s F,
but slightly lower dewpoints from more BL mixing and downsloping off
the Ozark Plateau. As a result, heat index values could end up being
slightly lower despite these warmer temperatures, which precludes
confidence required to extend the Heat Advisory through Wednesday.
On Thursday, the closer approach of the front and increasing cloud
cover also introduces uncertainty on exact high temperatures.

While 40 to 60 percent of ensemble model guidance has showers and
thunderstorms develop across the Central Plains on Wednesday,
reaching northeastern MO/west-central IL Wednesday night while
likely weakening; higher (60 to 80 percent) probabilities exist on
Thursday with the cold front actually reaching the CWA. There is
still variability in the timing of the cold front, determining how
much of the CWA will have a favorable passage of the front during
peak heating. There is a loose consensus of a passage Thursday
evening into night with ensemble model-derived joint probabilities
of 1000+ J/kg SBCAPE and 30+ kt deep-layer wind shear are 40 to 60
percent across central/northeastern MO and west-central IL,
supporting the potential for a few strong to severe thunderstorms.
However, the exact coverage and longevity of thunderstorms Thursday
night is not completely clear with deep-layer shear and large-scale
ascent and instability generally decreasing with time and southward
extent Thursday night. There is enough uncertainty with the details
of the severe weather setup and the long lead time, that severe
weather is not being messaged for Thursday at this time.

After Thursday, global model guidance continue to advertise varying
flavors of upper-level flow becoming quasi-zonal persisting across
the Mid-Misssissippi River Valley through the upcoming weekend. This
pattern will be favorable for continued chances of showers and
thunderstorms at times with the front wavering northward and
southward, modulated by passing shortwave troughs. These patterns
have notoriously low predictability, so it is difficult to discern
any details, but it does look like most of the time will be dry
versus wet. With the CWA spending most of this time after Thursday
on the cool side of the front, cooler high temperatures are
expected, closer to average.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 629 PM CDT Mon Jun 8 2026

While there will be a chance for showers and thunderstorms through
late morning on Tuesday, the best chance will be through 03Z at
UIN and the St. Louis area terminals and then again between 07-12Z
at COU/JEF with a thunderstorm complex that will be moving in
from western Missouri. If this complex continues to move east and
maintains strength, then it will pose a threat to the St. Louis
area terminals after 12Z, though confidence is not high enough to
include in the TAFs at this time. Any of the heavier showers and
thunderstorms may reduce visibilities and ceilings to MVFR or
possible IFR conditions in brief heavy rain with possible wind
gusts over 25 knots. Otherwise, winds outside of thunderstorms are
expected to stay 12 knots or lower.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Tuesday morning for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Jefferson MO-Lincoln MO-Marion MO-Moniteau MO-Monroe MO-
     Montgomery MO-Osage MO-Pike MO-Ralls MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

     Heat Advisory from noon to 10 PM CDT Tuesday for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
     Montgomery MO-Osage MO-Reynolds MO-Saint Charles MO-Saint
     Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Warren MO-Washington MO.

IL...Flood Watch through Tuesday morning for Adams IL-Bond IL-Brown
     IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

     Heat Advisory from noon to 10 PM CDT Tuesday for Calhoun IL-
     Jersey IL-Madison IL-Monroe IL-Randolph IL-Saint Clair IL.

&&

$$

WFO LSX