705  
FXUS63 KFSD 182359  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
659 PM CDT SAT AUG 18 2018  
   
SHORT TERM
 
(THIS EVENING THROUGH MONDAY)  
ISSUED AT 302 PM CDT SAT AUG 18 2018  
 
ASIDE FROM SMOKE, ACTIVE WEATHER BEGINS TO RETURN TO THE REGION  
TONIGHT AS AN UPPER WAVE APPROACHES FROM THE WEST. THE INITIAL ROUND  
OF PRECIPITATION SHOULD BE IN THE FORM OF CONVECTION WEST OF OUR CWA  
WHICH COULD EVENTUALLY SPREAD INTO AREAS WEST OF THE JAMES RIVER  
LATE THIS EVENING. INSTABILITY LOOKS TO BE SIZABLE WITH MUCAPE  
VALUES GREATER THAN 2000 J/KG AND, WITH MARGINAL WIND SHEAR SEEN ON  
MODEL HODOGRAPHS, CAN'T RULE OUT A SEVERE STORM OR TWO. WITH  
CONVECTIVE INHIBITION INCREASING AS NIGHT SETS IN AND BEING HIGHER  
EAST OF THE JAMES IN GENERAL, NOT EXPECTING ANY SEVERE STORMS TO  
REMAIN THAT WAY AS THEY HEAD EAST TOWARD THE I-29 CORRIDOR.  
 
UPPER TROUGH CONTINUES TRANSLATING SOUTHEASTWARD ACROSS NE FOR  
SUNDAY WITH PLENTY OF FORCING FOR SHOWERS AND A FEW STORMS  
THROUGHOUT THE DAY. WITH PWAT VALUES AT OR ABOVE 1.5 INCHES,  
EXPECTING LIGHT TO MODERATE RAIN ACROSS MOST OF THE CWA WITH TWO  
POCKETS OF HIGHER TOTALS. THE PROGGED EVOLUTION OF THE SYSTEM  
SUGGESTS TWO FOCI FOR HIGHER TOTALS NEAR OUR CWA - BOTH FRONTAL  
BANDS ASSOCIATED WITH THE 850MB BOUNDARY. THE FIRST LOOKS TO OCCUR  
SUNDAY AFTERNOON ON OUR NORTHWESTERN BORDER BEFORE A SECOND BAND  
DEVELOPS LATER ON OUR SOUTHEASTERN BORDER AS THE UPPER LOW CONTINUES  
TO DIG INTO IOWA ON MONDAY. MOST OF OUR CWA WILL BE BETWEEN THESE  
TWO AREAS - IN PARTICULAR A CORRIDOR ROUGHLY ALONG AND JUST EAST OF  
A YKN-FSD-MML LINE. WITH THE NORTHWESTERN AREA GENERALLY BEING DRY  
THESE PAST FEW MONTHS, WILL NOT GO WITH ANY FLOOD/FLASH FLOOD WATCH  
IN THAT REGION. THE SOUTHEASTERN BAND WILL BE SOMETHING TO KEEP AN  
EYE ON IN FUTURE UPDATES FOR A WATCH, BUT AM NOT TOTALLY CONFIDENT  
ONE WILL BE NEEDED GIVEN QPF VALUES AND THE FACT THAT THIS SECOND  
FRONTAL BAND IS A RELATIVELY NEW DEVELOPMENT IN THE LAST FEW MODEL  
RUNS.  
 
AS FOR OTHER SENSIBLE WEATHER DURING THE SUNDAY/MONDAY PERIODS,  
COMPRESSED THE DIURNAL RANGE IN ACCORDANCE WITH EXPECTED OVERCAST  
CONDITIONS AND TWEAKED WINDS UPWARD ON MONDAY WHEN GUIDANCE  
AGREEMENT ON BOTH PRESSURE GRADIENT AND WIND DIRECTION WAS PRESENT.  
   
LONG TERM
 
(MONDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 302 PM CDT SAT AUG 18 2018  
 
AFTER THE RAIN TAPERS OFF MONDAY, NOT MUCH GOING ON IN THE  
EXTENDED BEFORE THE NEXT WAVE APPROACHES FOR THURSDAY/FRIDAY. THIS  
PATTERN WILL ONCE AGAIN DRIVE SOUTHERLY WINDS WEDNESDAY NIGHT  
THROUGH FRIDAY, SO HAVE BUMPED UP WINDS AND TEMPERATURES  
ACCORDINGLY. THIS WAVE LOOKS TO BE MORE OPEN THAN THE WAVE TO  
START THE WEEK AND THUS POPS ARE CONFINED TO A MUCH SHORTER  
PERIOD. WHILE CAPE VALUES THURSDAY AFTERNOON WOULD BE SUBSTANTIAL  
GIVEN LOW LEVEL TEMPERATURES AND MOISTURE, CAPPING, LIKE ALWAYS,  
LOOKS TO BE A SIGNIFICANT FACTOR, ESPECIALLY AROUND THE I-29  
CORRIDOR.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)  
ISSUED AT 657 PM CDT SAT AUG 18 2018  
 
LIGHT SOUTH AND SOUTHEAST WINDS CONTINUE THIS EVENING AS A FRONT  
APPROACHES FROM THE WEST. THIS FRONT BRINGS SHOWERS AND  
THUNDERSTORMS WITH LOCALLY GUSTY WINDS AND WILL MOVE THROUGH  
PLACES NEAR CHAMBERLAIN AND HURON, SD BETWEEN SUNSET AND MIDNIGHT.  
THIS LINE OF STORMS WEAKENS AS IT HEADS FURTHER EAST DURING THE  
EARLY MORNING HOURS. THROUGHOUT SUNDAY RAIN CHANCES INCREASE  
ACROSS THE REGION AS A LARGER WEATHER SYSTEM MOVES IN. MID-LEVEL  
CLOUD DECKS WILL BE COMMON, WITH AFTERNOON THUNDERSTORMS AGAIN  
POSSIBLE. STRONG STORMS LOOK UNLIKELY, BUT ISOLATED STRONGER  
THUNDERSTORMS COULD FEATURE SMALL HAIL SUNDAY AFTERNOON. EXPECT  
RAIN AT SOME POINT OVER THE NEXT 24 HOURS, WITH AN INCH OR MORE  
FOR SOME.  
 

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

 
 

 
 
SHORT TERM...FERGUSON  
LONG TERM...FERGUSON  
AVIATION...VANDENBOOGART  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SD Page
The Nexlab IA Page
The Nexlab MN Page
The Nexlab NE Page Main Text Page