Severe Thunderstorm Warning 204, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
107 PM CDT Sat Jul 4 2026

.KEY MESSAGES...

- Dangerously hot and humid conditions with heat index values
  from around 100-105 continue today. Heat Advisories and an
  Extreme Heat Warning remain in effect until 800 PM.

- There is a chance for thunderstorms today and tonight. Some
  storms may be strong to severe and capable of producing 50-60
  mph winds as well as hail up to 1 inch in diameter and locally
  heavy downpours.

- The chance for showers and thunderstorms continues into early
  next week, with temperatures closer to normal in the mid 80s to
  around 90.

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 343 AM CDT Sat Jul 4 2026

Convective trends are very difficult to forecast today. Clusters
of thunderstorms over northwest Missouri and central Illinois are
pushing outflow boundaries east and south respectively. More
convection may continue to pop up over central Missouri as well,
which will reinforce the boundary if it gets strong enough. Either
boundary is a potential focus for thunderstorm development today,
and the boundaries could collide which would also be a great
forcing mechanism for convective development.

Clouds from morning convection that linger into the afternoon and/or
continuing scattered afternoon convection would almost certainly
suppress temperatures and end the excessive heat today. However,
timing and coverage is uncertain given the complex interactions
which will take place today.  If coverage remains limited this
morning, temperatures could easily recover to reach heat index
values between 95-105. While this isn't as hot as earlier in the
week, the duration of this heat wave continues to support the
current headlines, particularly since there will be a lot of people
outside for Independence Day celebrations. GFS and RAP show 2000-
4000 J/Kg CAPE developing this afternoon with as much as 25kts of
deep layer shear.  This would support multi-cell clusters with the
potential to produce damaging winds.  Think the chance for
thunderstorms will generally decrease in the evening with loss of
daytime heating, but there will still be a lingering thunderstorm
threat to Independence Day celebrations beyond sunset.

Carney

&&

.LONG TERM...  (Sunday through Friday)
Issued at 343 AM CDT Sat Jul 4 2026

There's little change to the remainder of the forecast for Sunday
through next Friday.  A short wave digs into the Mississippi Valley
Sunday which pushes a weak cold front through the area.  Global
guidance members diverge somewhat Monday in how they handle the
wave.  The GFS digs the base of the trough deep into the Lower
Mississippi Valley where it fractures late Tuesday leaving a cut off
low over eastern Texas/western Louisiana.  The ECMWF begins this
process much earlier on Monday night which puts the cut off low
farther north over Oklahoma and Arkansas.  The more northern
solution seems to be favored by the NBM and the LREF mean which are
keeping precipitation chances going at least through Tuesday as the
closed low moves slowly northeast and is finally reintegrated into
the mean flow.  While there's a relatively dry period on Wednesday,
precipitation chances return Thursday and Friday as another short
wave moves across the Mid Mississippi Valley.  Temperatures through
the period should be closer to seasonal normal as upper level long
wave ridging will remain well west of the area.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1255 PM CDT Sat Jul 4 2026

There is a threat for multiple rounds of thunderstorms at all of
the local terminals through the TAF period. Isolated to scattered
showers and storms are in the broader vicinity of all local
terminals except for KUIN, with these posing a threat for early in
the period. Our attention then turns to a cluster of storms moving
eastward out of western Missouri and a cold front sinking
southward into the region late this afternoon and evening.
Both will serve as a focus for a greater threat of thunderstorms
capable of erratic, gusty winds and heavy rainfall. Confidence is
low on the timing of these stronger storms, so chances have been
left to PROB30 groups for now. Once confidence increases, TEMPO or
prevailing groups will be needed for some of the terminals. A lull
in rain chances is expected tonight, with a low chance for showers
and thunderstorms again late in the period tomorrow.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 8 PM CDT this evening for Audrain MO-
     Crawford MO-Iron MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Monroe MO-Pike MO-Ralls MO-Reynolds MO-Saint
     Francois MO-Shelby MO-Washington MO.

     Extreme Heat Warning until 8 PM CDT this evening for Boone MO-
     Callaway MO-Cole MO-Franklin MO-Gasconade MO-Jefferson MO-
     Moniteau MO-Montgomery MO-Osage MO-Saint Charles MO-Saint
     Louis City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO.

IL...Heat Advisory until 8 PM CDT this evening for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin
     IL-Marion IL-Montgomery IL-Pike IL.

     Extreme Heat Warning until 8 PM CDT this evening for Clinton IL-
     Madison IL-Monroe IL-Randolph IL-Saint Clair IL-Washington
     IL.

&&

WFO LSX

Preliminary Local Storm Report
National Weather Service St Louis MO
217 PM CDT Sat Jul 4 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0213 PM     Tstm Wnd Dmg     1 W California          38.63N 92.58W
07/04/2026                   Moniteau           MO   Trained Spotter

            6 inch tree limb snapped on west side of
            California with the gust front passage.

&&

AE

Preliminary Local Storm Report
National Weather Service St Louis MO
337 PM CDT Sat Jul 4 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0315 PM     Tstm Wnd Dmg     2 E Weldon Spring       38.72N 90.60W
07/04/2026                   St. Charles        MO   Public

            Power lines down.

&&

BRC