Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

212
FXUS63 KLSX 212024
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
324 PM CDT Sun Jun 21 2026

.KEY MESSAGES...

- Damaging winds and tornadoes are possible through this evening
  across east central and southeast Missouri into southwest Illinois.

- Locally heavy rainfall is also possible through early tonight.

- Seasonably cool conditions are forecast this work week.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 324 PM CDT Sun Jun 21 2026

A remnant MCV is currently in southwest Illinois and moving
east/northeast. There has been a very slow and gradual uptick in
convection out ahead of this feature across southwest and south-
central Illinois as diurnal instability continues to increase.
Low- level shear and helicity remain quite strong, so mini
supercells may be capable of producing tornadoes. This threat will
continue at least over the next few hours as the MCV progress
through south- central Illinois.

Farther southwest, additional showers and thunderstorms are expected
to develop farther southwest along the trailing cold front. Exactly
where and when is not certain, but my best guess would be near the
Missouri-Kansas border where surface convergence is located. At
least scattered storms should develop farther northeast eventually
along the boundary, with storms moving east/southeast in time. How
organized this convection will be is also uncertain as there are a
couple of limiting factors including: 1) weak surface convergence
along the boundary and 2) modest height rises behind the MCV. In
addition, the prior storms have at least helped limit instability
slightly, with MLCAPE values of 1000-1500 J/kg. Effective shear also
decreases behind the MCV, though is still near 30 knots. A mixed
mode of convection seems most likely, with multicellular clusters,
small bowing segments, and transient supercells all possible.
Damaging winds and a tornado or two are possible through late
evening before storms begin to move out to the southeast. Locally
heavy rainfall is also possible given high precipitable water values
(~1.9"). Afternoon/evening storms are however focused farther
southwest. Storms also should be progressive, so overall I think the
flash flood threat is low and likely would be isolated to any areas
that do experience some training.


Gosselin

&&

.LONG TERM...  (Monday through Next Sunday)
Issued at 324 PM CDT Sun Jun 21 2026

(Monday - Monday Night)

Cooler weather along with northerly winds and clouds are
expected on Monday. High temperatures are only expected to reach
into the mid 70s, or about 10 degrees below normal for the date.
Lows Monday night are forecast to drop into the mid 50s to near the
60 degree mark.


(Tuesday - Next Sunday)

Not much has changed with respect to the work week forecast with
broad northwest flow aloft across the Mississippi Valley. There is
high confidence in seasonally cool temperatures with mostly dry
weather expected outside of a cold frontal passage
Wednesday/Wednesday night.

Moderating temperatures are forecast heading into next weekend with
flow aloft becoming more zonal. That means increasing
moisture/instability as well and increasing chances of showers and
thunderstorms.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1227 PM CDT Sun Jun 21 2026

Showers and thunderstorms are expected to move out of the metro
St. Louis terminals over the next 2 hours. Additional development
is expected later this afternoon, but may be just south of both
central Missouri and St. Louis terminals. The actual cold front
should move through from northwest to southeast through tonight,
with winds veering from the southwest to the northwest and
eventually north/northeast through the period. Low stratus is also
forecast behind this front, with a period of IFR ceilings likely.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 1 AM CDT Monday for Franklin MO-Saint Charles
     MO-Saint Louis City MO-Saint Louis MO.

     Flood Watch through Monday morning for Crawford MO-Iron MO-
     Jefferson MO-Madison MO-Reynolds MO-Saint Francois MO-
     Sainte Genevieve MO-Washington MO.

     Flood Watch until 7 PM CDT this evening for Boone MO-Callaway MO-
     Cole MO-Gasconade MO-Lincoln MO-Moniteau MO-Montgomery MO-
     Osage MO-Warren MO.

IL...Flood Watch until 1 AM CDT Monday for Bond IL-Fayette IL-Greene
     IL-Jersey IL-Macoupin IL-Madison IL-Montgomery IL.

     Flood Watch through Monday morning for Clinton IL-Marion IL-
     Monroe IL-Randolph IL-Saint Clair IL-Washington IL.

     Flood Watch until 7 PM CDT this evening for Calhoun IL.

&&

$$

WFO LSX