062  
FXUS63 KLSX 201802  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED AVIATION  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
102 PM CDT WED JUN 20 2018  
   
UPDATE
 
 
ISSUED AT 1150 AM CDT WED JUN 20 2018  
 
QUICK UPDATE TO RAISE TEMPS ACROSS PORTIONS OF CENTRAL AND NE MO  
AND INTO WEST CENTRAL IL. KEPT TEMPS ELSEWHERE AS-IS FOR NOW.  
WHILE THE SHOWERS FROM THIS MORNING HAVE DELAYED WARMING, ONCE  
THOSE AREAS BEGIN TO MIX OUT, TEMPS SHUD CLIMB QUICKLY. EVEN WITH  
SLIGHTLY WARMER TEMPS, EXPECT HEAT INDEX VALUES TO REMAIN BELOW  
THE CENTURY MARK THIS AFTERNOON.  
 
STILL EXPECT ISOD TO SCT TSRA TO GRADUALLY DEVELOP THIS AFTERNOON.  
THE BEST CHANCES FOR STORMS WILL BE JUST AHEAD OF AN APPROACHING  
CDFNT. STORMS ARE EXPECTED TO PERSIST AHEAD OF THE FNT THRU MUCH  
OF TONIGHT. HOWEVER, THERE IS EXPECTED TO BE A BRIEF LULL LATE  
THIS EVENING INTO THE EARLY MORNING HOURS, BEFORE STORM REDEVELOP  
AHEAD OF THE FNT.  
 
TILLY  
 

 
   
SHORT TERM
 
(THROUGH LATE TONIGHT)  
ISSUED AT 340 AM CDT WED JUN 20 2018  
 
A CLUSTER OF SHOWERS AND A FEW THUNDERSTORMS THAT HAVE DEVELOPED  
NEAR THE I-70 CORRIDOR LAST EVENING HAS MAINTAINED ITSELF THE PAST  
FEW HOURS WITH THE MOST EXTENSIVE DEVELOPMENT ENTERING THE WESTERN  
HALF OF THE STL METRO AREA. THIS DEVELOPMENT CAN BE ATTRIBUTED TO  
WHAT LOOKS LIKE A MCV IN THE VICINITY WITH AN OLD OUTFLOW BOUNDARY  
FURTHER HELPING THINGS ALONG FOR AREAS FURTHER EAST INTO SOUTHERN  
IL. SKIES WERE MOSTLY CLOUDY ACROSS OUR REGION EARLY THIS MORNING  
WITH TEMPERATURES IN THE UPPER 60S AND LOWER 70S.  
 
THE MCV SHOULD SLOWLY SLITHER ITS WAY EAST NORTHEASTWARD WITH THE  
MID LEVEL FLOW AND THE AREA OF SHOWERS AND A FEW STORMS BEING DRIVEN  
BY IT WILL TAKE SEVERAL HOURS TO EXIT TO THE EAST. LOCALIZED HEAVY  
RAINFALL WILL STILL BE POSSIBLE UNTIL THIS EXITS BEING A VERY SLOW  
MOVING FOCUS THAT PROMOTES TRAINING OF ECHOES. A LULL IS THEN  
EXPECTED FOR MOST AREAS DURING MID AND LATE MORNING. HEADING INTO  
PEAK HEATING DURING THE AFTERNOON, A SIMILAR SETUP IS THEN EXPECTED  
FROM MOST OF THE RECENT PAST DAYS WITH WEAK SHEAR (LESS THAN 25KTS 0-  
6KM), MODERATE INSTABILITY (1000-2000 J/KG MLCAPE), VERY WEAK CINH,  
WITH NO OBVIOUS MECHANISMS TO FOCUS CONVECTION IN ANY ONE PLACE OVER  
ANOTHER, WITH SCATTERED THUNDERSTORMS EXPECTED.  
 
A FEATURE THAT LOOKS LIKE IT WILL ACT AS A FOCUS IS A LOBE OF  
VORTICITY, AN ARM OF LIFT ASSOCIATED WITH AN APPROACHING UPPER LO.  
THIS UPPER LO IS CURRENTLY OVER THE INTERFACE OF WYOMING/MONTANA AND  
IS EXPECTED TO TRACK SOUTHEASTWARD TOWARDS OUR REGION BY LATE THIS  
AFTERNOON. IT WILL THIS LOBE OF VORTICITY FROM THIS APPROACHING  
UPPER LO THAT SHOULD BE JUST WEST OF OUR FORECAST AREA BY MID TO  
LATE AFTERNOON AND SHOULD ENHANCE AND INCREASE CONVECTION FOR  
NORTHEAST AND CENTRAL MO WITH WHAT DOES RESULT HERE THEN TRACKING  
NORTHEASTWARD HEADING INTO THE EVENING HOURS. BY OVERNIGHT, THE  
UPPER LO ITSELF WILL BE IN CLOSE PROXIMITY ENOUGH TO MAINTAIN  
PERSISTENT CHANCE POPS.  
 
MAX TEMPS TODAY WILL RANGE FROM 85 TO 90 MOST AREAS, A WELCOME BREAK  
FROM THE PERSISTENT AND DANGEROUSLY HIGH LEVELS OF HEAT AND HUMIDITY  
SINCE LATE LAST WEEK. MIN TEMPS TONIGHT WILL RANGE FROM 65 TO 70  
MOST AREAS, WITH LOW 70S IN THE STL METRO AREA.  
 
TES  
   
LONG TERM
 
(THURSDAY THROUGH TUESDAY)  
ISSUED AT 340 AM CDT WED JUN 20 2018  
 
THE UPPER LO WILL CONTINUE TRACKING SLOWLY SOUTHEASTWARD, INTO  
NORTHERN MO BY LATE THURSDAY AFTERNOON, THRU THE STL METRO AREA  
FRIDAY MORNING AND INTO SOUTHEASTERN IL BY LATE FRIDAY AFTERNOON.  
THIS WILL BE A PRIMARY DRIVER OF OUR WEATHER FOR THIS TIME PERIOD,  
WITH GENERALLY HIGH POPS (PEAKING DURING THE AFTERNOON AND EARLY  
EVENING) AND AN EVEN COOLER STRETCH OF DAYTIME TEMPERATURES.  
 
WHILE SEVERE THUNDERSTORM POTENTIAL WILL BE LOW THURSDAY AND FRIDAY  
WITH LOW CAPE (LESS 1000 J/KG MLCAPE) FOR THIS TIME OF YEAR, SHEAR  
WILL BE BIT HIGHER THANKS TO MECHANICAL MIXING AROUND THE UPPER LO  
AND ADDING IN ENHANCED CYCLONIC FLOW, POTENTIAL FOR COLD AIR FUNNELS  
DOES APPEAR TO BE HIGHER FOR THOSE DAYS AND COULD BE THE MAIN SEVERE  
THREAT, SUCH AS IT IS.  
 
IN THE WAKE OF THE UPPER LO PASSING TO OUR EAST, THE SURFACE COLD  
FRONT SHOULD FINALLY MAKE ITS PUSH THRU OUR REGION AND SETTLE JUST  
TO OUR SOUTH FOR THE WEEKEND. A ZONAL FLOW IS EXPECTED TO EXIST  
ALOFT AND WILL CONTINUE TO SHUFFLE ALONG UPPER LEVEL DISTURBANCES TO  
MAINTAIN A STEADY RAIN THREAT FOR THE WEEKEND, BUT MAINLY IN  
SOUTHERN MO.  
 
ALREADY BY EARLY NEXT WEEK, THE UPPER RIDGE WILL BEGIN TO RE-ASSERT  
ITSELF INTO THE CENTRAL CONUS TO REMIND US THAT WE ARE NOW  
OFFICIALLY IN ASTRONOMICAL SUMMER, WITH ANOTHER ROUND OF SHOWERS AND  
THUNDERSTORMS EXPECTED AS A SURFACE WARM FRONT MOVES THRU AT THIS  
TIME.  
 
THANKS TO AN UPPER LO SLIDING THRU THURSDAY AND FRIDAY AND BEING ON  
THE COOL SIDE OF A FRONT FOR MUCH OF THE UPCOMING WEEKEND, LOOK FOR  
DAYTIME MAX TEMPS TO BE AT OR...WAIT FOR IT...BELOW AVERAGE...THRU  
THE WEEKEND WITH A RETURN TO ABOVE AVERAGE TEMPS FOR EARLY NEXT  
WEEK.  
 
TES  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 1230 PM CDT WED JUN 20 2018  
 
ISOD TSRA HAVE DEVELOPED ACROSS THE REGION EARLY THIS AFTERNOON.  
COVERAGE WILL CONTINUE TO INCREASE THRU THE AFTERNOON HOURS. THE  
BEST CHANCES, AND WHAT THE TAFS FOCUS ON, WILL BE WHAT IS EXPECTED  
TO BE A BROKEN LINE OF STORMS AHEAD OF AN APPROACHING CDFNT LATE  
THIS AFTERNOON AND INTO THE EARLY EVENING HOURS. A SECOND BRIEF  
ROUND OF STORMS IS EXPECTED LATE TONIGHT AT KUIN/KSUS/KCPS.  
REDEVELOPMENT IS EXPECTED AGAIN THURS MORNING ALONG THE FRONT.  
HOWEVER, AT THIS TIME, THIS REDEVELOPMENT IS EXPECTED TO BE EAST  
OF THE TERMINALS. OTHERWISE, MOISTURE TRANSPORT INTO THE REGION IS  
EXPECTED TO SUPPORT MVFR CIGS LATE TONIGHT INTO THURS MORNING.  
SOME UNCERTAINTY REMAINS AND GOING CIG FORECAST MAY BE TOO HIGH.  
 
SPECIFICS FOR KSTL: TSRA COVERAGE IS EXPECTED TO CONTINUE TO  
INCREASE THRU THE AFTERNOON HOURS. BEST CHANCES FOR TSRA IS EARLY  
THIS EVENING, HOWEVER, BRIEF IMPACTS EARLIER FROM STORMS IS ALSO  
POSSIBLE. OTHERWISE, EXPECT MVFR CIGS TO MOVE INTO THE REGION  
LATER TONIGHT AND SHUD LIFT THURS MORNING.  
 
TILLY  
 

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

 
 

 
 
WFO LSX  
 
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