083  
FXUS63 KFSD 230424  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1124 PM CDT MON MAY 22 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY)  
ISSUED AT 359 PM CDT MON MAY 22 2017  
 
A COUPLE AREAS OF ONGOING SHOWERS/THUNDERSTORMS WILL MOVE ACROSS THE  
REGION THE REMAINDER OF THIS AFTERNOON/EARLY EVENING. NORTHERN PARTS  
OF THE FORECAST AREA WILL SEE THE MORE WIDESPREAD ACTIVITY AHEAD  
OF LOW-MID LEVEL BOUNDARY DROPPING SOUTHWARD. WITH INSTABILITY MORE  
LIMITED IN THIS AREA DUE TO EXTENSIVE CLOUD COVER, THINK THE THUNDER  
THREAT WILL BE LIMITED.  
 
DISTINCT UPPER WAVE SPINNING THROUGH SOUTH CENTRAL SOUTH DAKOTA WILL  
BE CATALYST FOR MORE SCATTERED ACTIVITY ALONG/SOUTH OF I-90, AS IT  
SWINGS TOWARD NORTHWEST IOWA THROUGH THE LATE AFTERNOON, INTERACTING  
WITH SURFACE BOUNDARY DROPPING SOUTHWARD. MAY HAVE TO STILL WATCH  
FOR AN ISOLATED STRONGER STORM AS THESE COME TOGETHER OVER NORTHWEST  
IOWA/HIGHWAY 60 CORRIDOR OVER THE NEXT FEW HOURS, AND OUR SOUTHEAST  
FORECAST AREA WAS ABLE TO HEAT OUT MUCH MORE THAN LOCATIONS FARTHER  
WEST AND NORTH, AND THUS MAY HAVE SLIGHTLY BETTER INSTABILITY TO  
WORK WITH. THAT SAID, INSTABILITY PROFILES ARE STILL RATHER TALL AND  
SKINNY, AND WITH LIMITED SHEAR, STILL THINK THE HAIL THREAT WILL BE  
QUITE ISOLATED. CURRENT ACTIVITY IN SOUTH CENTRAL SOUTH DAKOTA AS  
BEEN ABLE TO PRODUCE GUSTS NEARING 40 MPH AT THE WINNER AIRPORT  
SHORTLY AFTER 230 PM, WHICH GOES ALONG WITH EARLIER THINKING THAT  
MARGINAL SEVERE WIND GUSTS MAY BE THE GREATER THREAT ACROSS OUR  
SOUTHEAST INTO THE VERY EARLY EVENING.  
 
LAGGING TAIL OF THE NORTHERN RAIN BAND MAY LINGER ACROSS SOUTHWEST  
MINNESOTA AND PORTIONS OF THE I-29 CORRIDOR INTO THIS EVENING. BUT  
OTHERWISE OVERNIGHT APPEARS RATHER QUIET, WAITING FOR NEXT WAVE TO  
DROP SOUTHWARD INTO THE AREA LATE TONIGHT/TUESDAY. MORE SUBSTANTIAL  
LOW LEVEL MOISTURE AND LOWER INSTABILITY WILL LEAD TO MAINLY SHOWER  
ACTIVITY. WITH CYCLONIC CURVATURE PREVAILING ACROSS THE AREA THROUGH  
THE DAY, POTENTIAL FOR SCATTERED SHOWERS WILL PERSIST THROUGHOUT THE  
DAYLIGHT HOURS. TEMPERATURES WILL ONCE AGAIN BE ON THE COOLER SIDE,  
WITH HIGHS IN THE 50S ACROSS THE REGION, AND A GUSTY NORTHERLY WIND  
MAKING IT FEEL A BIT MORE RAW.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH MONDAY)  
ISSUED AT 359 PM CDT MON MAY 22 2017  
 
LINGERING SHOWERS SHOULD MEET A FAIRLY QUICK DEMISE ON TUESDAY  
EVENING WITH LOSS OF DIURNAL CYCLE, BUT CLOUDS WILL BE FAIRLY  
PERSISTENT THROUGH AREAS EAST OF I-29 OVERNIGHT, ALONG WITH SOMEWHAT  
MORE PERSISTENT NORTHERLY WINDS HOLDING TEMPS IN THE MID 40S. TOWARD  
THE JAMES RIVER VALLEY AND WESTWARD, CLEARING AND PROXIMITY TO  
ELONGATED RIDGE AXIS SHOULD ALLOW A FEW TEMPS TO DIP TO THE CHILLY  
UPPER 30S. THE UPPER RIDGE FOLDS OVER AND PUSHES THE CLOSED LOW AWAY  
FROM THE REGION ON WEDNESDAY. SOME RESIDUAL MOISTURE LOOKS TO REMAIN  
TRAPPED BELOW SUBSIDENCE INVERSION FROM JUST WEST OF I-29 AND  
EASTWARD WHICH COULD RESULT IN SOME TEMPORARY SELF-DESTRUCTIVE  
SUNSHINE. HOWEVER, WILL LIKELY SEE SOME DRIER AIR ADVECTING IN ON  
NORTHEAST FLOW TOWARD SOUTHWEST MN WHICH SHOULD ERODE A THICKER  
COVERAGE, AS WELL AS SLOWLY DEEPENING MIXING OF WHAT SHOULD BE A  
THIN CLOUD LAYER. TEMPS SHOULD RECOVER 6 TO 10 DEGREES FROM THE  
TUESDAY CHILL, MAINLY 60S.  
 
TROUGH FROM THE PACIFIC NW WILL BARREL INTO THE RIDGE LATER  
WEDNESDAY NIGHT AND THURSDAY, FLATTENING THE RIDGE OVER THE NORTHERN  
PLAINS AND DRIVING A DECENT LOW LEVEL JET TOWARD SOUTH CENTRAL SD  
LATER IN THE NIGHT. MOISTURE IS QUITE LIMITED, BUT DO SEE SOME 700-  
500 HPA LAPSE RATES OF 7.5-8.5C/KM EXPAND INTO SOUTHEAST SD LATER  
WEDNESDAY NIGHT INTO THURSDAY. FOR NOW, NOT ENOUGH INDICATIONS OF  
DEEP DYNAMIC SUPPORT TO SUGGEST MUCH MORE THAN A MINIMAL THREAT FOR  
A MID-LEVEL SHOWER OR THUNDERSTORM, BUT SHOULD SEE SOME INCREASE IN  
CLOUDS THROUGH THE DAY THURSDAY. WAVE SHEARS A LITTLE CLOSER ON  
THURSDAY NIGHT AND HAVE TRENDED TOWARD A LOW-END CHANCE FOR ELEVATED  
THUNDERSTORMS MAINLY EAST OF I-29 ON THURSDAY NIGHT, AND LATER  
AT NIGHT ALONG ADVANCING WEAK FRONTAL BOUNDARY.  
 
FOCUS REMAINS AT ODDS WITH PRECIP CHANCES FRIDAY INTO FRIDAY NIGHT,  
WITH CORE OF THE UPPER TROUGH REMAINING NEAR/NORTH OF THE  
INTERNATIONAL BORDER, AND SECONDARY ENERGY DIGGING THROUGH THE  
CENTRAL AND SOUTHERN ROCKIES ALLOWING FOR A PERIOD OF FLATTER SUBTLY  
RISING HEIGHTS. FAIRLY "AVERAGE" TEMPERATURES EXPECTED.  
 
FROM SATURDAY ON BEGINS A TREK OF DEVIATING MODEL SOLUTIONS, FROM  
THE MORE PROGRESSIVE ECMWF WHICH SLINGSHOTS THE ROCKIES WAVE ACROSS  
THE CENTRAL PLAINS, KEEPING THE BOUNDARY WELL SOUTH, AND GRADUALLY  
SINKING THE NORTHERN VORTEX TOWARD THE GREAT LAKES. RESULT OF THIS  
SOLUTION IS A FAIRLY DRY AND TOUCH COOLER SOLUTION WITH STRONGER  
NORTHWEST FLOW BY SUNDAY. GFS ON THE OTHER END OF THE SPECTRUM  
REALLY AMPLIFIES THE WESTERN WAVE, CLOSES OFF AND CONGEALS INTO A  
STRONG CLOSED LOW WHICH WANDERS FROM EASTERN NEBRASKA TO WISCONSIN  
OVER A 36 HOUR PERIOD SUNDAY INTO MONDAY, WITH AN APPRECIABLE  
POTENTIAL OF RAINFALL. FOR NOW, TOO MUCH UNCERTAINTY TO GO ONE WAY  
OR THE OTHER, BUT EVEN GFS ENSEMBLE WOULD SUGGEST A MUCH GREATER  
PROBABILITY OF A NON-OPERATIONAL GFS SOLUTION. ONLY LOW POPS ARE IN  
ORDER, AND LIKELY TO HAVE TEMPS A SHADE BELOW TO NEAR NORMAL.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)  
ISSUED AT 1120 PM CDT MON MAY 22 2017  
 
SHOWERS WILL WORK OUT OF SOUTHWEST MINNESOTA THIS EVENING,  
HOWEVER, ADDITIONAL SHOWERS ALONG WITH MVFR CEILINGS WILL WORK  
BACK INTO THE REGION TOWARDS DAYBREAK ON TUESDAY. SHOWER ACTIVITY  
WILL BE LIGHT LEADING TO PREVAILING VFR CONDITIONS. WINDS WILL BE  
BRISK OUT OF THE NORTHWEST THROUGHOUT THE DAYLIGHT HOURS ON  
TUESDAY.  
 

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

 
 

 
 
SHORT TERM...JH  
LONG TERM...CHAPMAN  
AVIATION...BT  
 
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