Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

557
FXUS63 KLSX 280249
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
949 PM CDT Sat Jun 27 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms capable mainly of locally heavy
  rainfall and flash flooding are expected through this evening.

- Dangerous heat is expected Sunday through at least Thursday,
  with daily heat index values reaching 100-105 degrees. A Heat Advisory
  and Extreme Heat Warning are in effect for portions of the
  area.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 214 PM CDT Sat Jun 27 2026

An MCV can be seen swirling across southeastern Missouri heading
eastward into far southern Illinois this afternoon in visible
satellite imagery. The warm air advection wing of this system has
butted up against the stationary front that remains draped west to
east along the I-70 corridor, forcing scattered to widespread
convection mainly from the St. Louis metro eastward into Illinois.
This convection is occurring in an environment characterized by PWAT
around 2" and tropical-like thermal profiles, allowing for very
efficient rain rates. The threat for heavy rainfall and flash
flooding will continue across mainly Illinois through late this
afternoon and early evening before the MCV exits the region. Weak
subsidence in the wake of the MCV and rising heights thanks to a
building upper-level ridge will cause convective activity to notably
trend downward during the evening.

As the ridge continues to build into the Midwest overnight, the
stationary front will finally begin lifting northward as a warm
front. A low-level jet will ramp up overnight and interact with the
front, forcing isolated to scattered convection along it as it lifts
north-northeastward. The rising heights from the ridge are expected
to keep convection weaker and coverage more sparse than what is
occurring this afternoon.

Tomorrow, the ridge will continue to amplify over the Midwest, and
with the warm front then well to the north of the CWA, deep south-
southwesterly flow will begin advecting notably warmer air into the
region. Temperatures at 850mb will quickly rise into the low to mid-
20s C, climatologically favoring surface temperatures in the low to
mid 90s. Uninhibited surface flow from the Gulf will also keep low-
level moisture moving into the region, pairing with recent rainfall
and transpiration to push dewpoints into the mid to upper 70s. This
will produce heat index values of at least 100 degrees across a
majority of the CWA, with values around 105 within the St. Louis
metro area. Given the magnitude of heat and expected duration into
next week, the Heat Advisory remains unchanged, and the Extreme Heat
Watch for the St. Louis metro area has been upgraded to an Extreme
Heat Warning.

Elmore

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 214 PM CDT Sat Jun 27 2026

The period from Monday through Thursday is when confidence remains
highest in dangerous heat across the region, with both deterministic
guidance and ensemble clusters showing the upper-level ridge
remaining amplified over the Midwest. While guidance consensus has
850 mb temperatures peaking in the mid-20s C on Monday and gradually
cooling through the period, the hot start to the weak will allow the
heat to build and compound, keeping forecasted high temperatures
roughly in the mid-90s F and conditions dangerous through Thursday.

Starting Thursday, but particularly Friday and Saturday, a majority
of guidance has 850 mb temperatures cooling enough that there is a
low to medium chance that a few degrees will be knocked off daily
highs compared to earlier in the week. These cooling low to mid-
level temperatures will also allow for a low chance of airmass
thunderstorms that will provide at least localized heat relief. In
the end, the entire extended forecast period looks hot, with heat
index values around 105 degrees through the first half of the week
and around 100 degrees to end the week and start the holiday
weekend.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 939 PM CDT Sat Jun 27 2026

Scattered showers and thunderstorms are still expected to develop
overnight which may affect UIN and the St. Louis area terminals
between 06-10Z, so have maintained the PROB30 groups in those TAFS
with MVFR ceilings and visibilities. Outside of the thunderstorms,
there may still be MVFR (possible IFR) conditions through 13Z at
UIN until a warm front moves north through the area. Then dry and
VFR conditions are expected the rest of the period with southerly
winds winds.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon Sunday to midnight CDT Thursday night
     for Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Knox MO-Lewis MO-Lincoln
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Francois MO-
     Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO.

     Extreme Heat Warning from noon Sunday to midnight CDT Thursday
     night for Jefferson MO-Saint Charles MO-Saint Louis City MO-
     Saint Louis MO.

IL...Heat Advisory from noon Sunday to midnight CDT Thursday night
     for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette
     IL-Greene IL-Jersey IL-Macoupin IL-Marion IL-Montgomery IL-
     Pike IL-Randolph IL-Washington IL.

     Extreme Heat Warning from noon Sunday to midnight CDT Thursday
     night for Madison IL-Monroe IL-Saint Clair IL.

&&

$$

WFO LSX