St. Louis, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

616
FXUS63 KLSX 240335
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1035 PM CDT Mon Jun 23 2025

.KEY MESSAGES...

- Heat impacts will likely continue through at least Thursday,
  with heat index values reaching the upper 90s to near 105
  degrees at times. While the Extreme Heat Warning will be expired
  tonight at 9 PM, a Heat Advisory will remain in place until
  Thursday evening in many areas.

- A few showers and thunderstorms will be possible tomorrow
  afternoon and evening, with best chances (~30%) north of Highway
  36.

- Scattered showers and thunderstorms appear increasingly likely
  (30 to 50%) Friday through the weekend.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 251 PM CDT Mon Jun 23 2025

The primary concern in the short term remains the persistence of
impactful heat across much of the area, along with a limited (20-
30%) potential for showers and thunderstorms at times.

As we approach the hottest part of the day today, temperatures have
once again climbed into the low to mid 90s area-wide, with heat
index values in the upper 90s to near 105 thanks to dewpoints in the
low 70s. While this is certainly hot enough to generate localized
heat impacts to our more vulnerable populations, especially
considering that this is the third consecutive day of such heat and
is the first heat event of the year, it also falls a bit short of
Extreme Heat Warning thresholds across the St. Louis Metro area.
Meanwhile, many areas of northeast and central Missouri are not
likely to see heat index values above 100 degrees, and are also not
forecast to do so tomorrow either considering the potential for some
afternoon cloud cover and showers (more on that later).

While the magnitude of this heat has fallen slightly short of
projections, on the other hand, similar levels of heat are likely to
persist for at least two more days, as the upper ridge across the
eastern CONUS remains in place. As such, while it appears unlikely
that we will observe Warning-level significant heat impacts heading
into mid-week, the persistence of heat index values between 100-105
degrees across southeast Missouri, much of Illinois, and the St.
Louis metro area will prolong the potential for slightly lower-
end heat impacts through at least Thursday.

Given all of the above, we have made the following changes to our
ongoing heat headlines:

- The Extreme Heat Warning for the St. Louis metro area will expire
24 hours early at 9 PM tonight, and will replaced by a Heat
Advisory.

- Parts of the ongoing Heat Advisory in northeast / central
Missouri will also expire 24 hours early at 9 PM tonight.

- All remaining Heat Advisories, including the St. Louis metro area,
will be extended until 9 PM Thursday night.

Meanwhile, we will also need to keep an eye on the potential for a
few showers and thunderstorms, but later this afternoon/evening, and
again tomorrow afternoon / evening. Today`s potential is likely to
be limited to only a few very weak showers across mainly southeast
Missouri, where a healthy afternoon cumulus field has developed.
However, these showers would be developing within a very weakly
sheared environment underneath the upper ridge, and there is only
very limited support among high resolution guidance. As such, while
we can`t rule out a pinhead shower or two late this afternoon, this
potential is very limited and not expected to be particularly
impactful.

For tomorrow afternoon, a similar level of activity will be possible
in the afternoon and early evening south of the Highway 36 corridor,
with perhaps a slightly increased representation among CAMS. Still,
similar caveats apply, with very limited wind shear and forcing
available to create much more than a few run-of-the mill afternoon
showers. North of Highway 36 though, remnant convection forming
along a very weak stalled frontal boundary to our northwest may
drift into our area late in the afternoon and evening. While
afternoon instability is likely to be reasonably high (1500-2500
J/kg), weak wind shear (15-20kt of 0-6km shear) is once again
expected to be the limiting factor in spite of the the presence of a
very modest southwesterly mid-level jet. While there is a slightly
higher chance to see more substantial shower activity and a few
thunderstorms in these areas, the potential for strong/severe storms
appears limited even here.

BRC

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 251 PM CDT Mon Jun 23 2025

As we head into mid-week and beyond, all eyes will be on the
evolution of the large upper ridge across the Ohio Valley, which is
expected to very slowly de-amplify. This transition will likely have
two primary impacts on our local weather: temperatures are likely to
very slowly drop, while chances for showers and thunderstorms also
slowly increase.

While there remains some uncertainty regarding just how quickly it
will occur, medium and long range ensembles continue to indicate
that the upper ridge will slowly weaken from Wednesday onward, with
a transition to largely zonal flow across much of the CONUS.
Ensemble mean 500 mb height projections near the center of the ridge
drop from around 598 dam tomorrow to a more typical 591 dam by
Friday, while 850mb temperatures drop back to near or below the 90th
percentile. While this likely will only translate to a very steady
decrease in surface temperatures, perhaps by only a degree or two
each day, it is likely to eventually take us back to near or
slightly above average (and out of headline territory). As mentioned
in the short term section, we have opted to extend Heat Advisories
for many areas until Thursday, and while it`s possible that some
heat may linger another day, by Friday onward we should start to see
some more widespread improvement.

Meanwhile, the weakening of the upper ridge will also likely open
the door for increased chances for showers and thunderstorms,
particularly Friday through the weekend. Subtle shortwaves moving
through the increasingly zonal flow aloft will encounter less
resistance from the slowly weakening ridge, and with plenty of
humidity remaining in place, it stands to reason that showers and
thunderstorms will become increasingly likely. Ensemble projections
indicate that precipitation chances gradually increase to around 30-
50% by the end of the weekend, although it`s difficult to pinpoint
precise timing and coverage this early. We also can`t rule out a few
stronger showers / storms either, although weak flow aloft continues
to limit the overall potential for severe storms.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1028 PM CDT Mon Jun 23 2025

Light and variable surface flow will remain light and turn out of
the west-southwest Tuesday. A few thunderstorms could impact KUIN
with the best potential arriving during peak diurnal heating,
accounted for with PROB30. Thunderstorm potential is very low
further south with any potential likely isolated at best. If, by
chance, a thunderstorm impacts any site aside from KUIN, it`ll
likely need to be addressed via short term amendments. VFR
conditions are heavily favored through the period with cloud bases
remaining well above MVFR categories.

Maples

&&

.CLIMATE...
Issued at 1225 PM CDT Thu Jun 19 2025

Record maximum temperatures at St. Louis, MO (STL), Columbia, MO (COU),
and Quincy, IL (UIN) along with the year of the record:

    |    6/23    |    6/24    |    6/25
-------------------------------------------------------
STL | 101 (1930) | 102 (1988) | 103 (2024)
    |            |            |
COU | 100 (1988) | 103 (1988) | 102 (1988)
    |            |            |
UIN | 100 (1934) |  99 (1988) | 102 (1931)


Record high minimum temperatures at St. Louis, MO (STL), Columbia, MO (COU),
and Quincy, IL (UIN) along with the year of the record:

    |    6/23    |    6/24    |    6/25
------------------------------------------------------
STL | 80 (2010)  | 80 (1914)  | 82 (1988)
    |            |            |
COU | 76 (2010)  | 77 (1937)  | 77 (1988)
    |            |            |
UIN | 80 (1944)  | 79 (1931)  | 80 (1937)


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 9 PM CDT Thursday for Callaway MO-Cole MO-
     Crawford MO-Franklin MO-Gasconade MO-Iron MO-Jefferson MO-
     Lincoln MO-Madison MO-Montgomery MO-Osage MO-Pike MO-
     Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis
     City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO-
     Washington MO.

IL...Heat Advisory until 9 PM CDT Thursday 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