Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

125
FXUS63 KLSX 020343
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1043 PM CDT Wed Jul 1 2026

.KEY MESSAGES...

- Heat and humidity will remain at dangerous levels through
  Friday, with a low to medium chance for such conditions to
  continue into the Fourth of July.

- The chance for isolated to scattered showers and thunderstorms
  returns Thursday and continues through the weekend.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 253 PM CDT Wed Jul 1 2026

Upper-level ridging remains in place across the eastern United
States, but has begun showing signs of deamplifying. Nevertheless,
recent ACARS soundings out of KSTL show 850 mb temperatures just
above 20 degrees C, supporting temperatures in most locations right
now in the 90s with heat index values in the low 100s. With a few
more hours of heating yet to go, we`ll see values rise a few degrees
warmer.

The ridge weakens slightly tomorrow, and while this is not expected
to have a notable impact to temperatures when compared to today, it
will reduce capping. A majority of guidance has surface temperatures
reaching convective temperatures, and most of the HREF and REFS
members show isolated to scattered convection forming during the
afternoon. Conditions are most favorable for this convection across
southeastern Missouri and southwestern Illinois, where a low chance
(20%) for scattered showers and thunderstorms has been added to the
forecast. Ample instability and weak shear will lead to pulse
updrafts, and DCAPE forecast to be just over 1,000 J/kg leads to a
low chance for damaging downburst winds. If this threat
materializes, it is expected to remain very isolated.

Elmore

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 253 PM CDT Wed Jul 1 2026

For Friday into Saturday, confidence is high that the upper-level
ridge responsible for our recent heat will be deamplifying and
expanding westward. Temperatures as a result will cool slightly
compared to those during early to mid week, but by what rate is
uncertain - especially on Saturday. A series of shortwaves will be
moving through the Northern Plains and Upper Midwest on Saturday,
spawning convection along a front north of the CWA. This convection
may produce outflow and/or impact the speed of the effective front,
and this boundary may move into portions of the CWA around peak
heating. The phasing of shortwaves and subsequent positioning of the
front varies among guidance, with convection further south and
closer to the CWA providing a break from the heat for at least
portions of the CWA. Convection forming well north of the region
will lead to little to no impacts to the CWA, and this solution
would require an extension of heat headlines for at least portions
of the CWA through Saturday.

For Sunday and beyond, confidence decreases further in our day-to-
day weather. The front mentioned previously stalls somewhere across
the region thanks to flow over the CWA remaining quazi-zonal and the
ridge holding in place. This will favor chances for showers and
thunderstorms each day Sunday through Wednesday, with a majority of
ensemble members supporting this outcome. However, it will not be
constantly raining through this period, and a majority of guidance
does not support widespread heavy rainfall.

Both ensemble clusters and deterministic models support the ridge
remaining weaker through this portion of the period, but differ in
the placement of its axis and the phasing of shortwaves traversing
its crest. Between these factors and uncertainty in the position of
the front, confidence is low in temperature specifics. However,
ensembles are grouped around high temperatures typical for early
July (upper-80s/low-90s), with only a minority of guidance showing
high temperatures close to this recent stretch of heat.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1043 PM CDT Wed Jul 1 2026

VFR conditions are favored to extend through the end of the period
with light surface winds overnight. Winds remain relatively light
Thursday with the exception of an occasional gust during peak
diurnal mixing. A stray/isolated thunderstorm is possible with a
brief period of heavy rain and gusty winds. However, chances are
low (20%) and limited to hours through peak heating (20z-00z).
Any direct impacts to terminals will likely be handled via
amendments.

Maples

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Warning until 10 PM CDT Friday for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson 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 Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Extreme Heat Warning until 10 PM CDT Friday 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.

&&

$$

WFO LSX