673  
FXUS63 KLSX 220950  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
450 AM CDT TUE JUL 22 2025  
   
KEY MESSAGES
 
 
-THE EXTREME HEAT WARNING HAS BEEN DOWNGRADED TO A HEAT ADVISORY IN  
MOST LOCATIONS OUTSIDE THE BROADER ST. LOUIS METRO AREA. THE  
REMAINDER OF THE EXTREME HEAT WATCH HAS BEEN CONVERTED TO A HEAT  
ADVISORY STARTING WEDNESDAY AT NOON.  
 
-CONFIDENCE IS GROWING IN A BRIEF REPRIEVE FROM ADVISORY/WARNING  
LEVEL HEAT FRIDAY AND INTO THE WEEKEND BEFORE CHANCES INCREASE  
FOR ANOTHER HEAT WAVE NEXT WEEK.  
 

 
   
SHORT TERM
 
(THROUGH LATE WEDNESDAY AFTERNOON)  
ISSUED AT 249 AM CDT TUE JUL 22 2025  
 
THE MID-MISSISSIPPI VALLEY STILL SITS UNDER A MID-LEVEL RIDGE, WITH  
STRONG LOW-LEVEL SOUTHWESTERLY FLOW. THE SUBSEQUENT WARM AIR  
ADVECTION WILL PUSH HIGH TEMPERATURES BACK INTO THE 90S ACROSS MUCH  
OF THE AREA, EXCEPT ACROSS PORTIONS OF WEST-CENTRAL ILLINOIS WHERE  
EASTERLY FLOW WILL PULL COOLER TEMPERATURES IN FROM THE OHIO RIVER  
VALLEY. HIGH-LEVEL CLOUD DEBRIS FROM A DECAYING MCS OVER KANSAS WILL  
LIMIT HEATING SOMEWHAT FROM ITS MAXIMUM POTENTIAL, SO I LOWERED  
TODAY'S HIGHS A FEW DEGREES COMPARED TO PREVIOUS FORECASTS.  
 
THESE WARM TEMPERATURES COMBINED WITH HIGH HUMIDITY WILL BRING A  
RENEWAL OF OPPRESSIVE HEAT CONDITIONS ACROSS MUCH OF THE AREA WITH  
HEAT INDEX VALUES REACHING ABOVE 105 ACROSS MUCH OF THE AREA. OVER  
WEST-CENTRAL ILLINOIS WHERE HIGH TEMPERATURES WILL PEAK IN THE UPPER  
80S, HEAT INDEX VALUES ARE EXPECTED TO REACH THEIR MAXIMUM AROUND  
100 DEGREES. GIVEN THAT WE WILL NOT REACH SINGLE OR MULTI-DAY HEAT  
ADVISORY CRITERIA IN THIS LOCATION, I HAVE ISSUED A HEAT ADVISORY IN  
THIS AREA STARTING WEDNESDAY AT NOON AND CONTINUING UNTIL THURSDAY  
AT 7 PM. THERE IS NO HEAT PRODUCT IN EFFECT FOR THIS AREA TODAY.  
 
CONFIDENCE IS GROWING THAT THE CURRENT HEAT WAVE WILL BREAK, AT  
LEAST BRIEFLY, ON FRIDAY AND WE DON'T HAVE ANY PLANS TO CONTINUE THE  
CURRENT HEAT PRODUCTS BEYOND THURSDAY EVENING. WE ARE NO LONGER ABLE  
TO MEET EXTREME HEAT WARNING CRITERIA (105F FOR 4 DAYS, OR 110F FOR  
1 DAY) OUTSIDE OF THE METRO AREA THANKS TO THE PREVIOUS FEW DAYS OF  
CONVECTIVE INTERFERENCE. THEREFORE I HAVE DOWNGRADED MUCH OF THE  
WARNING AREA TO A HEAT ADVISORY, LEAVING THE ST. LOUIS METRO WITHIN  
THE EXTREME HEAT WARNING WHERE CONFIDENCE IS HIGH THAT WE WILL REACH  
AT LEAST 1 DAY OF 110F HEAT INDEX VALUES.  
 
WHILE THE MAJORITY OF TODAY WILL BE DRY, MOST HI-RES GUIDANCE IS  
SHOWING BRIEF, ISOLATED SHOWERS AND THUNDERSTORMS POPPING UP THIS  
AFTERNOON NEAR AND EAST OF THE MISSISSIPPI RIVER. THIS WEAK  
CONVECTION IS POPPING OFF OF EITHER A SMALL MID-LEVEL DISTURBANCE  
WITHIN THE RIDGE, OR THE REMAINS OF THE MCV ASSOCIATED WITH THE  
DECAYING MCS OVER KANSAS. REGARDLESS, THE WIDESPREAD HEIGHT RISES  
AND WEAK 0-6KM SHEAR ACROSS THE REGION WILL LIMIT CONVECTIVE  
DEVELOPMENT. THESE SHORT LIVED AND SPARSE SHOWERS AND THUNDERSTORMS  
ARE NOT EXPECTED TO MAKE A SIGNIFICANT DENT IN THE MAXIMUM  
TEMPERATURE AND HEAT INDEX VALUES TODAY.  
 
THE MID-LEVEL RIDGE WILL DEEPEN OVERNIGHT, STRENGTHENING THE  
SUBSIDENCE ACROSS THE REGION WEDNESDAY. AS A RESULT, WEDNESDAY IS  
EXPECTED TO BE DRY WITH LESS CLOUD COVER, PUSHING TEMPERATURES AND  
HEAT INDEX VALUES A FEW DEGREES HIGHER THAN TODAY.  
 
DELIA  
 

 
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH MONDAY)  
ISSUED AT 249 AM CDT TUE JUL 22 2025  
 
THE MID-LEVEL RIDGE WILL BEGIN TO PUSH SOUTHWARD THURSDAY, BRINGING  
THE WESTERLIES CLOSER TO THE MID-MISSISSIPPI VALLEY. THIS WILL PLACE  
THE MID-MISSISSIPPI VALLEY BACK IN MORE ACTIVE SOUTHWESTERLY FLOW,  
INCREASING THE POTENTIAL FOR CLOUD COVER WHICH MAY STUNT HIGH  
TEMPERATURES AND MAXIMUM HEAT INDEX VALUES. BY FRIDAY THE MID-LEVEL  
RIDGE WILL WEAKEN AND EXTEND ACROSS THE SOUTHERN HALF OF THE CONUS,  
LEAVING THE REGION WITHIN QUASI-ZONAL FLOW AND OPEN TO NUMEROUS  
DISTURBANCES MOVING THROUGH THE FLOW. CONFIDENCE IS INCREASING THAT  
PRECIPITATION AND ASSOCIATED CLOUD COVER WILL BE ENOUGH TO BRING A  
SLIGHT COOL DOWN TO TEMPERATURES FRIDAY TO BRING AN END TO THE  
ADVISORY/WARNING LEVEL HEAT.  
 
THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS LINGERS THROUGH THE  
WEEKEND AS THE MID-LEVEL FLOW EVOLVES FROM QUASI-ZONAL DURING THE  
FIRST HALF OF THE WEEKEND TO NORTHWESTERLY ON THE ADVANCING SIDE OF  
A RIDGE DURING THE SECOND HALF. BOTH POSITIONS LEAVE THE REGION OPEN  
TO SHOWERS AND THUNDERSTORMS. CLUSTER ANALYSIS OF THE GLOBAL  
ENSEMBLES SHOWS A LOT OF AGREEMENT IN THE RIDGE RESTRENGTHENING OVER  
THE CENTRAL CONUS, WHICH WOULD THROW US BACK INTO A HOT WEATHER  
REGIME. DETAILS WILL MATTER HOWEVER, IN HOW HOT AND WHETHER THIS  
WILL LEAD TO ADDITIONAL HEADLINES. THE LOCATION OF THE RIDGE,  
CHANCES FOR PRECIPITATION, CLOUD COVER, AND HUMIDITY WILL ALL PLAY A  
ROLE IN DETERMINING THE NEED FOR HEADLINES NEXT WEEK.  
 
DELIA  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)  
ISSUED AT 448 AM CDT TUE JUL 22 2025  
 
VFR CONDITIONS WILL CONTINUE THROUGH THE REMAINDER OF THE TAF  
PERIOD UNDER LARGELY DRY CONDITIONS. THERE IS A 20% CHANCE OF  
ISOLATED SHOWERS AND THUNDERSTORMS THIS AFTERNOON, MAINLY NEAR THE  
ST. LOUIS METRO TERMINALS. CONFIDENCE IN THUNDERSTORM DEVELOPMENT  
IS VERY LOW, SO HAVE NOT INCLUDED A MENTION IN THE TAFS FOR NOW.  
 
SOUTHEASTERLY WINDS WILL PREVAIL WITH SPEEDS LESS THAN 10 KTS.  
 
DELIA  
 

 
   
LSX WATCHES/WARNINGS/ADVISORIES
 
 
MO...HEAT ADVISORY FROM NOON TODAY TO 7 PM CDT THURSDAY FOR KNOX MO-  
LEWIS MO-MARION MO-MONROE MO-PIKE MO-RALLS MO-SHELBY MO.  
 
HEAT ADVISORY UNTIL 7 PM CDT THURSDAY FOR AUDRAIN MO-BOONE MO-  
CALLAWAY MO-COLE MO-CRAWFORD MO-GASCONADE MO-IRON MO-  
LINCOLN MO-MADISON MO-MONITEAU MO-MONTGOMERY MO-OSAGE MO-  
REYNOLDS MO-SAINT FRANCOIS MO-SAINTE GENEVIEVE 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 FROM NOON TODAY TO 7 PM CDT THURSDAY FOR ADAMS IL-  
BROWN IL-CALHOUN IL-CLINTON IL-PIKE IL-WASHINGTON IL.  
 
HEAT ADVISORY UNTIL 7 PM CDT THURSDAY FOR MADISON IL-RANDOLPH IL.  
 
EXTREME HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR MONROE IL-SAINT  
CLAIR IL.  
 

 
 

 
 
WFO LSX  
 
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