209  
FXUS63 KFSD 222256  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
556 PM CDT SAT JUL 22 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH SUNDAY)  
ISSUED AT 221 PM CDT SAT JUL 22 2017  
 
A WEAK SHORT WAVE IS MOVING ACROSS OUR SOUTHERN ZONES AT THIS TIME.  
IT IS LARGELY RESPONSIBLE FOR CREATING A LOT OF MID AND UPPER LEVEL  
CLOUDS EXTENDING FROM CENTRAL NEBRASKA INTO OUR SOUTHERN ZONES WHICH  
HAS MODIFIED OUR TEMPERATURES COOLER A BIT THIS AFTERNOON FOR MANY  
AREAS SOUTH OF I 90. PUT IN A LOW ISOLATED POP FOR OUR ZONES IN  
SOUTH CENTRAL SD LATE THIS AFTERNOON DUE TO SOME VERY SKITTISH  
ACTIVITY IN SOUTHWEST SD AT THIS TIME. THERE IS A STRONG PV GRADIENT  
ALONG THE 1.5 PRESSURE SURFACE IN THAT AREA THROUGH 00Z DENOTING THE  
SHORT WAVE, WITH AN EXITING JET STREAK FURTHER EAST IN SOUTHERN  
MINNESOTA PLACING THIS AREA IN THE RIGHT REAR QUAD OF THE JET.  
THEREFORE LARGE SCALE ASCENT IS ENHANCED. ML CAPE IS VERY THIN IN  
THAT AREA THIS AFTERNOON HOWEVER, WITH 30 KNOTS OF 0-6KM SHEAR AND  
UNIDIRECTIONAL SOUNDINGS OUT OF THE NORTHWEST. SO NOT EVEN SURE IF  
ANY ACTIVITY OCCURS AT ALL, IF IT WILL GENERATE MUCH IN THE WAY OF  
LIGHTNING/THUNDER. THE DRY DEW POINTS HAVE BEEN SLOW TO ENTER OUR  
FORECAST AREA, AND ONE CAN SEE THE AFFECTS OF RECENT RAINFALL IN  
HURON AND BROOKINGS THE PAST WEEK OR TWO, AS THEIR TEMPERATURES ARE  
STILL ONLY IN THE LOWER 80S DESPITE BEING MOSTLY SUNNY ALL DAY.  
 
AS THE SHORT WAVE IN OUR SOUTHERN ZONES, AND UPPER TROUGH TO OUR  
NORTHEAST MOVE AWAY FROM THIS REGION, THE DRIER AIR WILL FINALLY  
ADVECT INTO OUR FORECAST AREA, WHICH SHOULD PRODUCE LOWS IN THE  
UPPER 50S TO LOWER 60S. SUNDAY WILL FEATURE A NORTHERLY SURFACE WIND  
AND FINALLY DRIER AIR. TEMPERATURES MIX TO HIGHS RANGING FROM THE  
UPPER 70S IN PARTS OF SOUTHWEST MN, TO NEAR 90 IN SOUTH CENTRAL SD.  
MOST LOCATIONS WILL BE IN THE SEASONAL 80S. THERE COULD VERY LIKELY  
BE SOME STRATUS MOVING SOUTHWARD INTO OUR NORTHEAST ZONES VERY LATE  
TONIGHT AND SUNDAY MORNING BEHIND THE DEPARTING UPPER TROUGH.  
HOWEVER THEY WILL SCOUR OUT NOT SEVERELY IMPACTING HIGHS FOR  
SOUTHWEST MN.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 221 PM CDT SAT JUL 22 2017  
 
SURFACE RIDGE SLIDES ACROSS THE FORECAST AREA SUNDAY NIGHT, AND WITH  
DRIER AIR MASS IN PLACE, SHOULD BE ABLE TO SEE LOWS FALL INTO THE  
UPPER 50S-LOWER 60S MOST AREAS. SOUTHERLY FLOW BEHIND THE RIDGE WILL  
BEGIN TO DRAW LOW LEVEL MOISTURE BACK INTO THE REGION MONDAY, THOUGH  
WILL NOT YET BE TO THE LEVELS WE HAVE SEEN OF LATE, WITH DEW POINTS  
IN THE LOWER-MID 60S EXPECTED BY LATE MONDAY. THERMAL RIDGE WILL  
ALSO WORK INTO OUR FAR WESTERN FORECAST AREA, PUSHING TEMPERATURES  
BACK INTO THE MID-UPPER 90S WEST OF THE JAMES RIVER. SUBTLE WAVE  
COULD BRING SOME SPOTTY SHOWERS/STORMS TO THE AREA MONDAY NIGHT, BUT  
MOST AREAS WILL REMAIN DRY.  
 
UPPER JET PUSHES INTO THE NORTHERN PLAINS, WITH THE AXIS NORTH OF  
OUR FORECAST AREA, ON TUESDAY, WITH THE ASSOCIATED WAVE DRAGGING A  
COOL FRONT INTO EASTERN SOUTH DAKOTA BY LATE IN THE DAY. THIS COULD  
BECOME A FOCUS FOR STORM DEVELOPMENT LATE TUESDAY/TUESDAY NIGHT,  
WITH BETTER FORCING FOCUSED IN NORTHERN PARTS OF THE AREA. UPPER JET  
PLACEMENT IS SOMEWHAT UNCERTAIN, BUT CONSENSUS PLACES AXIS NORTH OF  
THE NORTH DAKOTA/SOUTH DAKOTA BORDER. THIS PLACES GREATEST DEEP  
LAYER SHEAR NORTH OF HIGHWAY 14, WITH FAIRLY WEAK FARTHER SOUTH  
TOWARD I-90 AND POINTS SOUTHWARD. CANNOT RULE OUT AN ISOLATED STRONG  
TO SEVERE STORM DURING THIS PERIOD, THOUGH GREATER THREAT LOOKS TO  
BE TO OUR NORTH AT THIS TIME.  
 
MODEL CONSISTENCY SEEN AT THIS TIME YESTERDAY REGARDING PRECIP  
CHANCES WEDNESDAY NIGHT IS, AS ANTICIPATED, NO LONGER PRESENT, WITH  
GFS/ECMWF BOTH TRENDING DRIER FOR THIS PERIOD AS BOUNDARY MENTIONED  
ABOVE PUSHES SOUTH OF THE AREA BY LATE WEDNESDAY. WILL CONTINUE TO  
CARRY SOME CHANCE POPS FOR NOW, AS EARLIER ECMWF AND LATEST CANADIAN  
ARE SLOWER IN MOVING THE FRONT THROUGH THE AREA, AND THUS STILL A  
LITTLE MORE BOISTEROUS WITH THEIR CHANCES.  
 
LATE NEXT WEEK, SURFACE HIGH BEGINS TO DOMINATE ACROSS THE UPPER  
MISSISSIPPI VALLEY, WITH ANY SIGNIFICANT LOW LEVEL MOISTURE CUTOFF  
BY A BOUNDARY PUSHING THROUGH THE CENTRAL/SOUTHERN PLAINS. THIS  
SHOULD LEAD TO A FAIRLY DRY PERIOD THURSDAY-SATURDAY, WITH DAYTIME  
TEMPERATURES NEAR TO A FEW DEGREES BELOW NORMAL.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)  
ISSUED AT 555 PM CDT SAT JUL 22 2017  
 
VFR CONDITIONS EXPECTED AT TAF SITES THROUGH THE PERIOD.  
 

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

 
 

 
 
SHORT TERM...MJ  
LONG TERM...JH  
AVIATION...JM  
 
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