273
FXUS63 KLSX 221934
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
234 PM CDT TUE JUL 22 2025
KEY MESSAGES
- EXTREME HEAT WILL CONTINUE ON WEDNESDAY. SOME (BRIEF) RELIEF IS
POSSIBLE THURSDAY (NORTHEAST MISSOURI/WESTERN ILLINOIS) AND
FRIDAY (AREAWIDE) AS RAIN CHANCES RETURN.
SHORT TERM
(THROUGH LATE WEDNESDAY AFTERNOON)
ISSUED AT 223 PM CDT TUE JUL 22 2025
ISOLATED SHOWERS/WEAK THUNDERSTORMS MAY CONTINUE TO PERCOLATE INTO
EARLY THIS EVENING ACROSS PORTIONS OF EAST-CENTRAL AND SOUTHEAST
MISSOURI AS WELL AS SOUTHWEST ILLINOIS. BRIEF DOWNPOURS AND
LIGHTNING ARE THE MAIN THREATS, THOUGH CANNOT RULE OUT A WEAK
MICROBURST (GUSTS UP TO 40 MPH) OR TWO. VERY WEAK (<10 KNOTS)
DEEP-LAYER SHEAR SUGGESTS UPDRAFTS WILL REALLY STRUGGLE TO GROW
TOO TALL BEFORE THE RAIN-COOLED DOWNDRAFTS WEAKEN THE
SHOWERS/THUNDERSTORMS. BY LATE EVENING, ALL ACTIVITY SHOULD
DIMINISH AS INSTABILITY DROPS NEAR/JUST AFTER SUNSET.
TEMPERATURES TONIGHT WILL REMAIN ON THE MILD SIDE, AND IN MANY
LOCATIONS BE A COUPLE OF DEGREES WARMER THAN LAST NIGHT. WINDS WILL
REMAIN LIGHT, BUT THERE IS A SIGN FOR MORE WIDESPREAD CIRRUS TO MOVE
NORTHWARD INTO THE AREA OVERNIGHT. IN ADDITION, TODAY'S HIGHS ARE
ALSO AT LEAST SEVERAL DEGREES WARMER THAN YESTERDAY.
EXTREME HEAT IS THE MAIN STORY ON WEDNESDAY, THOUGH THERE WILL BE
DIFFERENCES FROM WEST TO EAST IN THE "FLAVOR" OF HEAT. EAST OF THE
MISSISSIPPI RIVER, HIGHS IN THE LOW 90S ARE EXPECTED BUT WITH
DEWPOINTS IN THE UPPER 70S TO NEAR 80 DEGREES. FURTHER WEST,
ESPECIALLY ACROSS CENTRAL MISSOURI, DEEPER MIXING SHOULD YIELD
WARMER HIGH TEMPERATURES (UPPER 90S), BUT ALSO LOWER AFTERNOON
DEWPOINTS (UPPER 60S). THE END RESULT IN TERMS OF PEAK HEAT INDEX
IS ABOUT THE SAME NO MATTER HOW YOU SLICE IT: 100-110F ACROSS THE
AREA. THE HIGHEST READINGS SHOULD BE IN/AROUND METROPOLITAN ST.
LOUIS WHERE THE EXTREME HEAT WARNING CONTINUES.
GOSSELIN
LONG TERM
(WEDNESDAY NIGHT THROUGH NEXT TUESDAY)
ISSUED AT 223 PM CDT TUE JUL 22 2025
(WEDNESDAY NIGHT - SATURDAY NIGHT)
THE MID/UPPER LEVEL RIDGE CONTINUES TO SHIFT SOUTHEAST MORE INTO THE
MID SOUTH/OHIO VALLEY WEDNESDAY NIGHT INTO THURSDAY. THIS MAY BE FAR
ENOUGH SOUTH TO CAUSE SOME ISSUES WITH THE HEAT ON THURSDAY IN PARTS
OF OUR AREA, MORE SPECIFICALLY, IN NORTHEAST MISSOURI AND WEST-
CENTRAL ILLINOIS. DETERMINISTIC GUIDANCE LATE WEDNESDAY NIGHT SHOWS
A PRETTY STRONG LOW-LEVEL JET (30-40 KNOTS) VEERING MORE TO THE
SOUTHWEST BY THURSDAY MORNING. A MIDLEVEL SHORTWAVE TROUGH IS ALSO
FORECAST TO MOVE THROUGH THE MID-MISSOURI VALLEY INTO THE UPPER
MIDWEST. THERE IS SOME UNCERTAINTY AS TO HOW FAR SOUTH SHOWERS AND
THUNDERSTORMS WILL GET EARLY THURSDAY, BUT GIVEN A VEERING LOW-LEVEL
JET AND THE POSSIBILITY AT LEAST FOR A SOUTHWARD-PROPAGATING COLD
POOL, BELIEVE AT LEAST SOME SHOWERS AND THUNDERSTORMS MAY INFILTRATE
PARTS OF NORTHEAST MISSOURI AND WEST-CENTRAL ILLINOIS. AT THE VERY
LEAST, SOME THICKER MID/UPPER LEVEL CLOUDS SHOULD MOVE INTO THESE
AREAS. NEEDLESS TO SAY, ANY THUNDERSTORMS AND CLOUD COVER WILL HAVE
AN IMPACT ON TEMPERATURES. HIGHS WERE COOLED A BIT COMPARED TO THE
PREVIOUS FORECAST, CLOSER TO THE 90 DEGREE MARK. FURTHER SOUTHEAST,
THERE IS MORE CONFIDENCE IN A CONTINUATION OF THE EXTREME HEAT AS
TEMPERATURES CLIMB INTO THE MID TO UPPER 90S THURSDAY AFTERNOON.
PEAK HEAT INDEX VALUES OF 105-110 DEGREES ARE EXPECTED WITH THE
HIGHEST READINGS ONCE AGAIN MOST LIKELY IN/NEAR THE URBAN HEAT
ISLAND OF METROPOLITAN ST. LOUIS.
THURSDAY NIGHT INTO FRIDAY LOOKS LIKE A NEAR REPEAT OF WEDNESDAY
NIGHT/THURSDAY, WITH THE IMPORTANT CAVEAT IS THAT EVERYTHING LOOKS
TO FOCUS AT LEAST SLIGHTLY FURTHER SOUTH. THERE IS INCREASING
CONFIDENCE IN AT LEAST SCATTERED SHOWERS AND THUNDERSTORMS ACROSS
NORTHEAST MISSOURI AND WEST-CENTRAL ILLINOIS AS ANOTHER MIDLEVEL
SHORTWAVE TROUGH MOVES EASTWARD ON THE NORTHERN PERIPHERY OF THE
MID/UPPER RIDGE AXIS. TEMPERATURES IN NORTHERN SECTIONS OF THE AREA
WERE ALSO COOLED A COUPLE OF DEGREES, CLOSER TO THE MID 80S.
EXTENSIVE CLOUD COVER AND (LOWER) CHANCES OF SHOWERS AND
THUNDERSTORMS ALSO SHOULD IMPACT TEMPERATURES ACROSS THE I-70
CORRIDOR (IF NOT FURTHER SOUTH), BUT EXACTLY HOW MUCH WILL DEPEND
ON HOW ORGANIZED AND HOW FAR SOUTH ACTIVITY REACHES LATE FRIDAY
MORNING. GIVEN THIS UNCERTAINTY, THERE REMAINS NO PLANS ON
EXTENDING ANY HEAT HEADLINES INTO THE DAY ON FRIDAY. ANOTHER
SCENARIO FOR FRIDAY AFTERNOON/EVENING IS FOR REDEVELOPMENT OF
SHOWERS AND THUNDERSTORMS ALONG A COMPOSITE OUTFLOW BOUNDARY. THIS
ALSO COULD PUT A CAP ON AFTERNOON HIGH TEMPERATURES (AND HEAT
INDEX VALUES) DEPENDING ON HOW EARLY THIS ACTIVITY INITIATED.
SATURDAY'S HIGH TEMPERATURES ARE ALSO UNCERTAIN AS ANOTHER MCS MAY
DEVELOP. THIS ONE IS MORE LIKELY TO BE FURTHER NORTH AND EAST THAN
THE NIGHT BEFORE, BUT SHOWERS AND THUNDERSTORMS OR AT LEAST DEBRIS
CLOUDS COULD YIELD HIGHS STAYING AT OR BELOW 90 DEGREES. THIS WOULD
BE MOST LIKELY IN PARTS OF WEST CENTRAL AND SOUTH CENTRAL ILLINOIS,
BUT COULD SHIFT DEPENDING ON HOW FAST THE MID/UPPER LEVEL RIDGE
BUILDS BACK IN AND WHERE THE EFFECTIVE SURFACE FRONT IS LOCATED
(WHICH DEPENDS ON PRIOR ROUNDS OF CONVECTION).
(SUNDAY - NEXT TUESDAY)
THE MID/UPPER LEVEL HEIGHT PATTERN ACROSS THE CONUS HAS VERY LITTLE
VARIANCE INTO EARLY NEXT WEEK. ALL FOUR CLUSTERS OF THE 500-HPA
HEIGHT PATTERN DEPICT AN AMPLIFYING MID/UPPER LEVEL ANTICYCLONE
CENTERED ACROSS THE MID-MISSOURI VALLEY. THIS FEATURE SHOULD BE
STRONG ENOUGH (>99TH PERCENTILE 500-HPA HEIGHTS) TO KEEP OUR AREA
PRECIPITATION FREE. THIS MEANS THERE IS INCREASING CONFIDENCE IN A
RETURN (OR A CONTINUATION DEPENDING ON HOW THINGS EVOLVE THURSDAY-
SATURDAY) OF DANGEROUS HEAT SUNDAY INTO EARLY NEXT WEEK. HIGHS
RANGING FROM THE MID 90S TO NEAR 100 DEGREES ARE FORECAST, WITH
AFTERNOON HEAT INDEX VALUES PEAKING IN THE 105-110+ RANGE. BOTH THE
GEFS/EPS RETROGRADE THE ANTICYCLONE FAR ENOUGH WEST TO ALLOW FOR A
COLD FRONTAL PASSAGE, BUT THIS APPEARS MORE LIKELY AFTER TUESDAY AND
COULD OF COURSE CHANGE IN THE DAYS AHEAD.
GOSSELIN
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1233 PM CDT TUE JUL 22 2025
ISOLATED SHOWERS/WEAK THUNDERSTORMS ARE EXPECTED ACROSS PARTS OF
THE AREA TODAY, MAINLY IN SOUTHEAST MISSOURI AND SOUTHWEST
ILLINOIS. ACTIVITY SHOULD BE FOCUSED MOSTLY SOUTH OF THE TERMINALS
SO KEPT ANY MENTION OUT OF THE TAFS FOR NOW, BUT METRO SITES COULD
SEE A BRIEF DOWNPOUR/REDUCTION IN VISIBILITY. OTHERWISE, LOOK FOR
LIGHT SOUTHERLY WINDS AND VARIABLE CLOUDINESS. DIURNAL CUMULUS
SHOULD DISSIPATE THIS EVENING BEFORE RETURNING JUST BEFORE MIDDAY
ON WEDNESDAY.
GOSSELIN
LSX WATCHES/WARNINGS/ADVISORIES
MO...HEAT ADVISORY UNTIL 7 PM CDT THURSDAY FOR AUDRAIN MO-BOONE MO-
CALLAWAY MO-COLE MO-CRAWFORD 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 UNTIL 7 PM CDT THURSDAY FOR FRANKLIN MO-
JEFFERSON MO-SAINT CHARLES MO-SAINT LOUIS CITY MO-SAINT
LOUIS MO.
IL...HEAT ADVISORY FROM NOON WEDNESDAY TO 7 PM CDT THURSDAY FOR BOND
IL-FAYETTE IL-GREENE IL-JERSEY IL-MACOUPIN IL-MARION IL-
MONTGOMERY IL.
HEAT ADVISORY UNTIL 7 PM CDT THURSDAY FOR ADAMS IL-BROWN IL-
CALHOUN IL-CLINTON IL-MADISON IL-PIKE IL-RANDOLPH IL-
WASHINGTON IL.
EXTREME HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR MONROE IL-SAINT
CLAIR IL.
WFO LSX
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