621  
FXUS63 KLSX 101937  
AFDLSX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
237 PM CDT THU JUL 10 2025  
   
KEY MESSAGES
 
 
- MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED LATE  
FRIDAY THROUGH THE WEEKEND. A FEW SEVERE THUNDERSTORMS ARE  
POSSIBLE ACROSS NORTHEASTERN MO AND WEST-CENTRAL IL ALONG WITH  
LOCALLY HEAVY RAINFALL AND ISOLATED FLASH FLOODING.  
 
- HOT AND HUMID CONDITIONS ARE FORECAST ON FRIDAY WITH PEAK HEAT  
INDEX VALUES REACHING THE UPPER 90S TO NEAR 105 F, HIGHEST IN  
THE ST. LOUIS METRO. TEMPERATURES WILL COOL THROUGH THE WEEKEND.  
 

 
   
SHORT TERM
 
(THROUGH LATE FRIDAY NIGHT)  
ISSUED AT 233 PM CDT THU JUL 10 2025  
 
AN UPPER-LEVEL TROUGH WILL CONTINUE PASSING THROUGH THE MIDWEST THIS  
AFTERNOON AND EVENING. HOWEVER, WITH LARGE-SCALE ASCENT PASSING  
MAINLY NORTH OF THE CWA, WEAK CAPPING INVERSIONS, AND A LACK OF LOW-  
LEVEL CONVERGENCE, ONLY A STRAY SHOWER/THUNDERSTORM OR TWO IS  
EXPECTED AT MOST ACROSS NORTHEASTERN MO/WEST-CENTRAL IL THIS  
EVENING. A SHORTWAVE RIDGE WITH RISING MID-LEVEL HEIGHTS WILL BE  
UNFAVORABLE FOR ANY SHOWERS AND THUNDERSTORMS OVERNIGHT/FRIDAY  
MORNING ACROSS IA INTO NORTHERN IL FROM ADVANCING  
SOUTH/SOUTHEASTWARD INTO THE CWA. THEREFORE, PREDOMINANTLY DRY  
CONDITIONS ARE EXPECTED THROUGH MIDDAY FRIDAY. WEAK LOW-LEVEL  
SOUTHERLY FLOW/WAA WILL LEAD TO SLIGHTLY WARMER HIGH TEMPERATURES ON  
FRIDAY IN THE LOW TO MID-90S F. WITH INCREASING MOISTURE AND  
DEWPOINTS IN THE 70S F WITH SOME UPPER 60S F DURING PEAK AFTERNOON  
HEATING/BL MIXING, PEAK HEAT INDEX VALUES IN THE UPPER 90S TO NEAR  
105 F ARE FORECAST, HIGHEST IN THE ST. LOUIS METRO.  
 
AROUND 20 PERCENT OF HREF MEMBERSHIP HAS ISOLATED SHOWERS AND  
THUNDERSTORMS DEVELOPING DURING THE AFTERNOON ACROSS THE OZARKS AND  
SOUTHWESTERN IL WITH A SIGNAL FOR WEAK SURFACE CONVERGENCE (POSSIBLY  
TOPOGRAPHICALLY ENHANCED) AND CONVECTIVE TEMPERATURES TO BE REACHED.  
A WEAK MICROBURST WITH GUSTY WINDS CANNOT BE RULED OUT, BUT WARM MID-  
LEVEL TEMPERATURES/WEAK LAPSE RATES AND WEAK DEEP-LAYER WIND SHEAR  
MAY LIMIT UPDRAFT STRENGTH. INSTEAD, THE MAIN FOCUS OF SHOWERS AND  
THUNDERSTORMS WILL BE ACROSS SOUTHERN IA AND NORTHERN MO DURING THE  
AFTERNOON AND EVENING AS A SHORTWAVE TROUGH OVERSPREADS A COLD FRONT  
AND OTHER REMNANT OUTFLOW BOUNDARIES. IT IS UNCERTAIN HOW QUICKLY  
THESE SHOWERS AND THUNDERSTORMS WILL ADVANCE SOUTH/SOUTHEASTWARD  
INTO NORTHEASTERN MO AND WEST-CENTRAL IL WITH CAMS INDICATING AN  
ARRIVAL AS EARLY AS 4 PM AND LATE AS 8 PM, DEPENDING ON HOW QUICKLY  
COLD POOL DEVELOPMENT CAN OCCUR. DEEP-LAYER WIND SHEAR OF 20 TO 25  
KT AND MLCAPE OF 2000 TO 3000 J/KG WILL FAVOR MAINLY MULTICELL  
THUNDERSTORMS OR AN MCS WITH DAMAGING WINDS AND MARGINALLY SEVERE  
HAIL. WITH DEEP WARM CLOUD DEPTHS, PW APPROACHING 2", AND THE  
POTENTIAL FOR CELL TRAINING AND BACKBUILDING INTO A 35 KT-SOUTHWESTERLY  
LLJ THERE IS ALSO A THREAT OF LOCALLY HEAVY RAINFALL AND ISOLATED  
FLASH FLOODING. ALL OF THESE THREATS ARE HIGHEST ACROSS  
NORTHEASTERN MO AND WEST-CENTRAL IL WITH SHOWERS AND THUNDERSTORMS  
EXPECTED TO GRADUALLY WEAKEN WITH TIME AND SOUTHWARD EXTENT  
FRIDAY NIGHT AS THEY BECOME INCREASINGLY OUTFLOW DOMINANT.  
 
PFAHLER  
 

 
   
LONG TERM
 
(SATURDAY THROUGH NEXT THURSDAY)  
ISSUED AT 233 PM CDT THU JUL 10 2025  
 
ON SATURDAY, THE COLD FRONT WILL REACH THE CWA BEFORE IT SLOWS AND  
POSSIBLY WAVERS ACROSS THE REGION OVER THE WEEKEND. THERE SHOULD BE  
AN OVERALL SOUTHEASTWARD PROGRESSION OF THE FRONT WITH TIME, BUT  
THIS PROGRESSION IS UNCERTAIN DUE TO THE IMPACT OF MULTIPLE PASSING  
MID-LEVEL SHORTWAVE TROUGHS/MCVS WITHIN A VARIABLE PERIOD OF  
SOUTHWESTERLY FLOW AND ASSOCIATED SHOWERS AND THUNDERSTORMS.  
THEREFORE, ENSEMBLE MEMBERSHIP HAS A BROAD-BRUSHED AREA OF 50 TO 70  
PERCENT PROBABILITIES OF MEASURABLE RAINFALL THAT ENCOMPASS MOST OF  
THE CWA ON SATURDAY AND THEN SHIFT TO SOUTHEASTERN MO AND  
SOUTHWESTERN IL ON SUNDAY. WITH THE SLOW FRONT, SLOW OR TRAINING  
CELL MOTIONS, AND PW STRADDLING 2", THE THREAT OF LOCALLY HEAVY  
RAINFALL WILL EXIST BUT WHETHER OR NOT FLASH FLOODING OCCURS WILL  
HINGE ON MESOSCALE DETAILS THAT ARE STILL UNCERTAIN. WITH WEAK DEEP-  
LAYER WIND SHEAR, CONFIDENCE IS LOW IN ANY ORGANIZED SEVERE  
THUNDERSTORMS OVER THE WEEKEND. WITH A GRADUAL PASSAGE OF THE FRONT  
OVER THE WEEKEND AND INCREASING CLOUDS AND PRECIPITATION, A COOLING  
TREND WILL TAKE PLACE OVER THE WEEKEND WITH NEAR/SLIGHTLY BELOW  
AVERAGE HIGH TEMPERATURES IN THE 80S F NEARLY CWA-WIDE BY SUNDAY.  
 
A BROAD UPPER-LEVEL RIDGE WILL BRIEFLY DOMINATE THE MID-MISSISSIPPI  
RIVER VALLEY MONDAY INTO TUESDAY, ALLOWING THE AFOREMENTIONED FRONT  
TO EVENTUALLY LIFT BACK NORTHWARD ALONG WITH THE MOST FAVORABLE  
CORRIDOR OF SHOWERS AND THUNDERSTORMS. HOWEVER, THERE ARE LITTLE  
SIGNS OF ANY APPRECIABLE LARGE-SCALE FORCING WITH MAINLY SCATTERED  
DIURNAL SHOWERS AND THUNDERSTORMS EXPECTED. GLOBAL MODEL GUIDANCE  
THEREAFTER IS IN GENERAL AGREEMENT IN ANOTHER RELATIVELY ACTIVE/WET  
PERIOD DURING THE MIDDLE OF NEXT WEEK WITH UPPER-LEVEL QUASI-ZONAL  
TO SOUTHWESTERLY FLOW AND MULTIPLE PASSING SHORTWAVE  
TROUGHS/PERTURBATIONS. THE NBM HIGH TEMPERATURE DISTRIBUTION IS ALSO  
REASONABLY CLUSTERED (3 TO 5 F IQR) ON A WARMING TREND TO NEAR OR  
SLIGHTLY ABOVE AVERAGE THROUGH THE FIRST HALF OF THE WEEK ALONG WITH  
ANOTHER INCREASE IN MOISTURE/DEWPOINTS.  
 
PFAHLER  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)  
ISSUED AT 1225 PM CDT THU JUL 10 2025  
 
DRY AND VFR FLIGHT CONDITIONS WILL PERSIST THROUGH THE TAF PERIOD,  
ALTHOUGH THERE ARE LOW CHANCES (20 PERCENT OR LESS) OF ISOLATED  
SHOWERS AND THUNDERSTORMS THIS AFTERNOON/EVENING AT KUIN AND FRIDAY  
AFTERNOON AT KSTL. SINCE THESE PROBABILITIES/CONFIDENCE IS LOW, NO  
EXPLICIT MENTION HAS BEEN INCLUDED AT THIS POINT. SOUTHERLY WINDS  
TODAY WILL BECOME MORE SOUTHWESTERLY LATE FRIDAY MORNING.  
 
PFAHLER  
 

 
   
LSX WATCHES/WARNINGS/ADVISORIES
 
 
MO...NONE.  
IL...NONE.  

 
 

 
 
WFO LSX  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MO Page
The Nexlab IL Page Main Text Page