598  
FXUS63 KLSX 262026  
AFDLSX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
326 PM CDT WED JUL 26 2017  
   
SHORT TERM
 
(THROUGH LATE THURSDAY AFTERNOON)  
ISSUED AT 323 PM CDT WED JUL 26 2017  
 
PRIMARY CONCERN WILL TRANSITION THIS EVENING FROM HEAT TO LOCALIZED  
HEAVY RAINFALL. WILL BE TRIMMING FAR NORTHWESTERN PORTION OF HEAT  
ADVISORY OFF AS THICKER MIDLEVEL CLOUDS HAVE KEPT TEMPERATURES IN  
THE LOW 90S PREVENTING HEAT INDEX VALUES FROM APPROACHING 105F.  
REST OF ADVISORY STILL LOOKS GOOD AND WILL CONTINUE UNTIL 8PM.  
 
STILL LOTS OF UNCERTAINTY WITH RESPECT TO CONVECTIVE TRENDS FOR  
OVERNIGHT TONIGHT. RETREATING WARM FRONT IS CURRENTLY ACROSS THE  
MISSISSIPPI RIVER IN ILLINOIS AND CONTINUES TO PUSH NORTHEASTWARD.  
BELIEVE HEAVIEST AXIS OF RAINFALL MAY SET UP ROUGHLY ALONG THAT  
BOUNDARY WHICH IS FORECAST TO ALSO BE ROUGHLY COLLOCATED WITH  
STRONG UPPER-LEVEL FORCING FOR ASCENT VIA VORTICITY MAXIMA AND  
LOW-LEVEL MOISTURE CONVERGENCE. THIS AXIS HOWEVER WILL LIKELY STAY  
EAST/NORTHEAST OF THE CWA. SHOWERS AND THUNDERSTORMS WILL LIKELY  
FILL IN BEHIND THAT AREA ALONG TRAILING COLD FRONT. DUE TO COPIOUS  
AMOUNTS OF CLOUD COVER AND MORE STABLE AIR ACROSS THE LOWER-MID  
MISSOURI VALLEY, CONVECTION WILL LIKELY NOT BE AS RIGOROUS AS  
THOUGHT 24 HOURS AGO. NOT SEEING TOO MUCH OF A SEVERE THREAT AS  
FREEZING LEVELS ARE VERY HIGH WITH ONLY MODEST MIDLEVEL LAPSE  
RATES. CANNOT RULE OUT A WET MICROBURST HOWEVER IN A STRONGER  
CORE.  
 
MAIN CONCERN WITH CONVECTION TONIGHT WILL CONTINUE TO BE ON  
LOCALIZED HEAVY RAINFALL. THERE ARE QUITE A FEW MITIGATING FACTORS  
FOR WIDESPREAD FLASH FLOODING TONIGHT INCLUDING DRY ANTECEDENT  
CONDITIONS (AND LOW SOIL MOISTURE PERCENTILES), MORE STABLE AIR  
UPSTREAM THAN FORECAST 12-24 HOURS AGO MENTIONED ABOVE, AND VERY  
HIGH FLASH FLOOD GUIDANCE (2-3" IN ONE HOUR). THAT BEING SAID,  
WILL BE LEAVING THE FLASH FLOOD WATCH ALONE FOR NOW AS STILL  
EXPECTING A ROUND OF SHOWERS AND THUNDERSTORMS WITHIN THE WATCH  
AREA IN A VERY SUPPORTIVE ENVIRONMENT (DEEP WARM CLOUD DEPTHS AND  
VERY HIGH PWAT VALUES) FOR EFFICIENT PRECIPITATION PRODUCTION.  
TRAINING WOULD NEED TO OCCUR THOUGH TO PRODUCE PROBLEMS IN LOCAL  
AREAS.  
 
SCATTERED-NUMEROUS STORMS WILL CONTINUE ALONG AND AHEAD OF THE COLD  
FRONT THROUGH THE OVERNIGHT HOURS INTO EARLY THURSDAY MORNING  
BRINGING FOR MOST AREAS SOME VERY WELCOME RAINFALL. BELIEVE THERE  
WILL BE A LULL IN ACTIVITY DURING THE LATE MORNING HOURS BEFORE  
MOSTLY SCATTERED STORMS FIRE ALONG THE COLD FRONT IN THE EARLY  
AFTERNOON. HIGHEST POPS FOR THURSDAY AFTERNOON LOOK TO BE ACROSS  
PORTIONS OF SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS WHERE COLD  
FRONT IS EXPECTED TO BE LOCATED. LOCALIZED HEAVY RAINFALL AGAIN MAY  
BE POSSIBLE IF STORMS TRAIN ACROSS THE SAME AREAS.  
 
HIGH TEMPERATURES TOMORROW WILL BE QUITE A BIT COOLER THAN THAT OF  
TODAY DUE TO AN INCREASE IN CLOUD COVER AND CONVECTION. HIGHS IN THE  
MID 80S ARE LIKELY FOR MOST, WHICH IS NEAR TO SLIGHTLY BELOW NORMAL  
FOR LATE JULY.  
 
GOSSELIN  
 
   
LONG TERM
 
(THURSDAY NIGHT THROUGH NEXT WEDNESDAY)  
ISSUED AT 323 PM CDT WED JUL 26 2017  
 
HIGH PRESSURE WILL BUILD OVER THE REGION BY FRIDAY NIGHT. NORTHWEST  
FLOW WILL DOMINATE THE PATTERN THROUGHOUT THE FORECAST PERIOD.  
THE AREA WILL SEE TEMPERATURES BELOW CLIMATOLOGICAL NORMALS FOR  
BOTH AFTERNOON HIGHS AND MORNING LOWS ALONG WITH DRY WEATHER. HIGH  
PRESSURE ALOFT WILL MOVE WEST IN RESPONSE TO A SERIES OF SHORT  
WAVES DIVING SOUTH OUT OF THE HIGH PLAINS STARTING MONDAY MORNING.  
A WEAK BOUNDARY WILL SETUP IN SOUTHERN IOWA AHEAD OF A COLD FRONT  
THAT WILL IMPACT THE AREA LATER IN THE WEEK.  
 
KELLY  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 1237 PM CDT WED JUL 26 2017  
 
FEW DIURNAL SHOWERS AND THUNDERSTORMS JUST STARTING TO DEVELOP  
ACROSS PORTIONS OF SOUTHEAST MISSOURI AND SOUTHWEST ILLINOIS. ALSO  
WATCHING SLOWLY DECAYING SHOWERS APPROACHING FROM NORTHWESTERN  
MISSOURI. MAIN THREAT OF SHOWERS AND STORMS HOWEVER CONTINUES TO  
LOOK LIKE LATE EVENING THROUGH THE OVERNIGHT HOURS, FIRST  
AFFECTING KUIN, THEN KCOU, FOLLOWED BY METRO TERMINALS. ACTIVITY  
SHOULD WEAKEN/WANE THURSDAY MORNING BEFORE ADDITIONAL  
SHOWERS/STORMS FORM ALONG COLD FRONT. MVFR TO NEAR IFR CEILINGS  
LIKELY LATE TONIGHT/EARLY THURSDAY BEHIND THIS FRONT FOR KUIN.  
WINDS WILL ALSO SWING FROM THE SOUTHWEST TO THE NORTHWEST WITH  
THIS FRONTAL PASSAGE.  
 
SPECIFICS FOR KSTL:  
 
WATCHING SOME DIURNAL CONVECTION THIS AFTERNOON INTO EARLY THIS  
EVENING BUT BELIEVE COVERAGE TOO LOW WITH BRUNT OF ACTIVITY  
STAYING SOUTH OF THE TERMINAL. HIGHER CHANCE OF STORMS OVERNIGHT  
TONIGHT. IFR VISIBILITIES POSSIBLE IN ANY HEAVIER CORES. SHOULD BE  
A LULL IN ACTIVITY LATE THURSDAY MORNING BEFORE ADDITIONAL STORMS  
FIRE ALONG COLD FRONT IN VICINITY OF KSTL EARLY THURSDAY  
AFTERNOON. FRONT SHOULD PASS THROUGH WITH DRIER WEATHER AND A WIND  
SHIFT TO THE NORTHWEST BY MID AFTERNOON.  
 
GOSSELIN  
 

 
   
LSX WATCHES/WARNINGS/ADVISORIES
 
 
MO...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR CALLAWAY MO-COLE  
MO-CRAWFORD MO-FRANKLIN MO-GASCONADE MO-IRON MO-JEFFERSON  
MO-LINCOLN MO-MADISON MO-MONITEAU MO-MONTGOMERY MO-OSAGE MO-  
REYNOLDS MO-SAINT CHARLES MO-SAINT FRANCOIS MO-SAINT LOUIS  
CITY MO-SAINT LOUIS MO-SAINTE GENEVIEVE MO-WARREN MO-  
WASHINGTON MO.  
 
FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY  
MORNING FOR KNOX MO-LEWIS MO-MARION MO-SHELBY MO.  
 
IL...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR BOND IL-CALHOUN IL-  
CLINTON IL-FAYETTE IL-GREENE IL-JERSEY IL-MACOUPIN IL-  
MADISON IL-MARION IL-MONROE IL-MONTGOMERY IL-RANDOLPH IL-  
SAINT CLAIR IL-WASHINGTON IL.  
 
FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY  
MORNING FOR ADAMS IL-BROWN IL-PIKE IL.  
 

 
 

 
 
WFO LSX  
 
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