148  
FXUS63 KFSD 241717  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1217 PM CDT SUN JUN 24 2018  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 350 AM CDT SUN JUN 24 2018  
 
A LOW CONFIDENCE FORECAST IN TERMS OF CONVECTION INTO TONIGHT WITH  
MODEL DIFFERENCES AND NO SIGNIFICANT FORCING MECHANISMS TO LATCH ON  
TO. MUCH OF THE SHOWER AND THUNDERSTORM DEVELOPMENT MAY BE DRIVEN BY  
HEATING OF THE DAY AS INSTABILITY INCREASES ACROSS THE AREA.  
PRESENTLY SEEING A FEW ISOLATED SHOWERS OVER SOUTHWESTERN MN INTO  
THE IA GREAT LAKES AREA IN ASSOCIATION WITH A WEAK UPPER LEVEL VORT  
LOBE SWINGING THROUGH THE REGION. SHOULD SEE A DOWNTREND IN THIS  
ACTIVITY THROUGH THE MORNING HOURS AS THE LOBE PIVOTS OFF TO THE  
NORTHEAST. OTHERWISE, THE EARLY PART OF THE DAY WILL BE MOSTLY DRY,  
THEN AS ALLUDED TO ABOVE, SHOWERS AND THUNDERSTORMS ARE EXPECTED TO  
REDEVELOP IN THE AFTERNOON AS INSTABILITY INCREASES AND THERE IS  
SOME LOW LEVEL JET ENHANCEMENT OVER OUR EAST DURING THE AFTERNOON.  
SPC HAS AGAIN INCLUDED THE SOUTHERN PORTIONS OF OUR AREA IN A  
MARGINAL RISK FOR TODAY, WHICH SEEMS REASONABLE WITH CAPE VALUES  
HOVERING AROUND 2000 J/KG AND BULK SHEAR OF 25 TO 30 KTS. ANY SEVERE  
STORMS WOULD BE ISOLATED, WITH LARGE HAIL/SEVERE WIND THE GREATEST  
THREATS. HIGHS TODAY WILL BE SIMILAR OF LATE - IN THE UPPER 70S TO  
LOWER 80S.  
 
AGAIN, CONFIDENCE IN CONVECTIVE DEVELOPMENT IS NOT ESPECIALLY HIGH  
FOR TONIGHT WITH VARYING MODEL SOLUTIONS, THOUGH IT DOES APPEAR THAT  
SHOWER AND THUNDERSTORM COVERAGE WILL INCREASE, ESPECIALLY LATER AT  
NIGHT AS THE WELL ADVERTISED UPPER LEVEL LOW BEGINS TO SLIDE  
EASTWARD OUT OF THE WESTERN HIGH PLAINS. OVERNIGHT QPF AMOUNTS WILL  
REMAIN IN CHECK - AVERAGING LESS THAN HALF AN INCH ACROSS THE  
AREA. LOWS WILL RUN IN THE MID TO UPPER 60S.  
   
LONG TERM
 
(MONDAY THROUGH SATURDAY)  
ISSUED AT 350 AM CDT SUN JUN 24 2018  
 
THE CLOSED UPPER LEVEL LOW WILL TRACK DIRECTLY OVER OUR AREA FOR THE  
MONDAY INTO EARLY TUESDAY TIME FRAME. WHAT IS SOMEWHAT ENCOURAGING  
IS THAT ALL MODELS HAVE SHIFTED THE HEAVIER PRECIPITATION WITH THE  
SYSTEM WEST OF INTERSTATE 29 - AWAY FROM AREAS THAT RECEIVED THE  
GREATER RAINFALL WITH LAST WEEK'S SYSTEM. BOTH THE GFS AND NAM PLACE  
THE MAXIMUM PRECIPITATION AXIS OVER THE WESTERN JAMES RIVER VALLEY,  
WHILE THE ECMWF IS A LITTLE FARTHER TO THE EAST - KEEPING IT JUST  
WEST OF I-29. THE HEAVIEST RAINFALL WILL OCCUR DURING THE DAY ON  
MONDAY, WITH LOCALES WEST OF I-29 RECEIVING 1 TO 2 INCHES DURING  
THAT PERIOD, WITH AMOUNTS LESS THAN AN INCH BACK TO THE EAST OF THAT  
AREA. RAINFALL AMOUNTS ARE EXPECTED TO BE LESS ON MONDAY NIGHT AS  
THE BETTER PRECIPITATION PIVOTS TO THE NORTH AND EAST AROUND THE  
LOW. SCATTERED SHOWERS/THUNDERSTORMS WILL LINGER INTO TUESDAY AS THE  
SYSTEM BEGINS TO PULL AWAY, WITH ONLY LIGHT RAINFALL AMOUNTS  
EXPECTED. AS IT STANDS NOW, RAINFALL TOTALS FOR THE ENTIRE EVENT -  
LATE TONIGHT INTO TUESDAY WILL AVERAGE 2 TO 3 INCHES WEST OF I-29,  
TO 1 TO 2 INCHES TO THE EAST.  
 
FOR THE REMAINDER OF THE WEEK, THE UPPER LEVEL PATTERN EVOLVES INTO  
AN UPPER LEVEL RIDGE BY THE END OF THE WEEK, WITH TEMPERATURES  
WARMING INTO THE MID AND UPPER 80S. RAIN CHANCES WILL BE MINIMAL FOR  
WEDNESDAY THROUGH FRIDAY. BY NEXT WEEKEND, MODELS ARE IN DECENT  
AGREEMENT ON A UPPER LEVEL TROUGH DEVELOPING OVER THE WESTERN CONUS,  
WHICH BEGINS TO NUDGE EASTWARD OVER THE WEEKEND. THIS WILL BRING  
INCREASING RAIN CHANCES AND SLIGHTLY COOLER TEMPERATURES.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1214 PM CDT SUN JUN 24 2018  
 
MVFR CEILINGS WILL REMAIN POSSIBLE THROUGH MID AFTERNOON BUT AFTER  
THIS CEILINGS SHOULD BE VFR. SHOWERS AND THUNDERSTORMS ARE  
EXPECTED TO BECOME MORE WIDESPREAD AFTER ABOUT 23Z AND ESPECIALLY  
AFTER 5Z. ADDITIONAL MVFR CEILINGS AND POSSIBLY VISIBILITIES WILL  
BE POSSIBLE LATE TONIGHT AND MONDAY MORNING.  
 

 
   
FSD WATCHES/WARNINGS/ADVISORIES
 
 
SD...NONE.  
MN...NONE.  
IA...NONE.  
NE...NONE.  

 
 

 
 
SHORT TERM...JM  
LONG TERM...JM  
AVIATION...08  
 
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