060  
FXUS63 KFSD 171723  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1223 PM CDT TUE SEP 17 2019  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 409 AM CDT TUE SEP 17 2019  
 
ONGOING SHOWERS AND STORMS EARLY THIS MORNING EXPECTED TO EXIT BY  
12Z OR VERY SHORTLY AFTER, AS MID-LEVEL WAVE LIFTS NORTHEAST OF THE  
AREA. REMAINDER OF TODAY SHOULD BE QUIET, BUT CONTINUED WARM, HUMID  
AND WINDY AS 30-45 KT LOW LEVEL WINDS MIX DOWN TO THE SURFACE.  
MOMENTUM TRANSFER THROUGH THE MIXED LAYER INDICATES POTENTIAL FOR  
GUSTS OF 25-35KTS, STRONGEST NORTH OF I-90, AND ESPECIALLY IN HIGHER  
ELEVATIONS OF SOUTHWEST MINNESOTA. WITH GOOD MIXING AND LESS CLOUD  
COVER INT HE WAKE OF THE DEPARTING WAVE, SHOULD BE ABLE TO ATTAIN  
HIGHS IN THE MID-UPPER 80S MOST AREAS.  
 
TONIGHT, A STRONGER WAVE LIFTS NORTH-NORTHEAST THROUGH THE WESTERN  
DAKOTAS, REACHING EASTERN NORTH DAKOTA/SOUTHERN MANITOBA BY 12Z  
WEDNESDAY. THIS WAVE EXPECTED TO REMAIN FAR ENOUGH NORTHWEST THAT IT  
WILL NOT DIRECTLY LEAD TO STORM CHANCES IN OUR AREA TONIGHT. HOWEVER  
A COOL FRONT EXTENDING SOUTHWARD FROM THE ASSOCIATED SURFACE LOW  
PUSHES INTO EASTERN SOUTH DAKOTA THIS EVENING, AND CONTINUES SLOWLY  
EASTWARD OVERNIGHT, WITH SOME DISAGREEMENT AMONG THE MODELS IN JUST  
HOW QUICKLY THE BOUNDARY MOVES EAST. SOMEWHAT BETTER AGREEMENT IN  
DEPICTION OF 40-50+KT LOW LEVEL JET REDEVELOPING AHEAD OF THE  
BOUNDARY, WHICH SHOULD TRIGGER AT LEAST SCATTERED, MAINLY ELEVATED  
STORMS. FROM LATE EVENING INTO THE OVERNIGHT HOURS. MID-LEVEL LAPSE  
RATES ARE ONLY MARGINALLY UNSTABLE, AND EFFECTIVE SHEAR IS ON THE  
WEAK SIDE, SO WIDESPREAD SEVERE WEATHER IS NOT EXPECTED. HOWEVER,  
CANNOT RULE OUT AN ISOLATED STRONGER STORM WHICH MAY BE ABLE TO DRAG  
THE STRONGER WINDS ALOFT BRIEFLY TO THE SURFACE.  
 
IN ADDITION, PRECIPITABLE WATER VALUES AHEAD OF THE COOL FRONT  
INCREASE TO 1.5-2". AS LOW LEVEL JET VEERS TO MORE SOUTHWESTERLY  
OVERNIGHT, COULD SEE SOME TRAINING STORMS, WHICH COULD RESULT IN  
LOCALLY HEAVY RAINFALL IN PARTS OF SOUTHWEST MN/NORTHWEST IA.  
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 409 AM CDT TUE SEP 17 2019  
 
ANY OVERNIGHT STORMS TONIGHT SHOULD EXIT OUR FAR SOUTHEAST COUNTIES  
BY MID MORNING WEDNESDAY, THOUGH SURFACE BOUNDARY LAGS AND KEEPS A  
SMALL CHANCE OF ADDITIONAL SHOWERS/STORMS ACROSS OUR FAR SOUTHEAST  
THROUGH THE DAY. THIS BOUNDARY BECOMES A FOCAL POINT FOR ADDITIONAL  
STORMS WEDNESDAY NIGHT AS ANOTHER WAVE TRACKS NORTHEAST ATOP THE  
BOUNDARY. SOME QUESTION ON EXACTLY WHERE THE LOW LEVEL BOUNDARY WILL  
BE LOCATED, THOUGH CONSENSUS APPEARS TO BE OVER NORTHEAST NEBRASKA  
AND NORTHWEST IOWA, SO WILL MAINTAIN OUR HIGHEST POPS/QPF SOUTH OF  
VERMILLION TO SPIRIT LAKE LINE WEDNESDAY NIGHT INTO EARLY THURSDAY,  
WITH LESSER POPS/QPF ACROSS SOUTHEAST SOUTH DAKOTA AND SOUTHWEST  
MINNESOTA. AGAIN, LACK OF DEEP LAYER SHEAR AND MEAGER MID-LEVEL  
INSTABILITY LEAD TO GREATER CONCERN FOR LOCALLY HEAVY RAIN RATHER  
THAN SEVERE WEATHER DURING THIS PERIOD.  
 
BRIEF REPRIEVE FROM THE UNSETTLED PATTERN LATER THURSDAY/THURSDAY  
NIGHT, BUT FRIDAY-SATURDAY CONTINUES TO LOOK LIKE A MORE ACTIVE  
PERIOD AS MAIN UPPER TROUGH SWINGS OUT INTO THE PLAINS. STILL SOME  
UNCERTAINTY IN STRENGTH/POSITION OF THE UPPER TROUGH, WITH GREATER  
CONSENSUS SLOWLY TRACKING THE MAIN WAVE NORTHWEST OF OUR FORECAST  
AREA FRIDAY NIGHT-SATURDAY. ASSOCIATED SURFACE COLD FRONT MOVES INTO  
CENTRAL SD FRIDAY LATE AFTERNOON/EVENING, WITH AMPLE INSTABILITY  
DEVELOPING IN THE WARM SECTOR EAST OF THE BOUNDARY, AND LITTLE  
CONVECTIVE INHIBITION NOTED BY AFTERNOON, SO SHOULD SEE SHOWERS AND  
STORMS BECOME MORE NUMEROUS THROUGH THE AFTERNOON/EVENING. SPC HAS  
AREAS WEST OF A KYKN-KMML HIGHLIGHTED IN THE DAY 4 OUTLOOK, BUT MID  
LEVEL LAPSE RATES ARE MARGINALLY UNSTABLE, AND DEEP LAYER SHEAR ON  
THE WEAK SIDE EAST EXCEPT PERHAPS IN OUR FAR WESTERN COUNTIES, SO  
SEVERE WEATHER RISKS ARE SOMEWHAT UNCERTAIN AT THIS RANGE.  
 
SYSTEM APPEARS SLOWER TO EXIT THAN IN MODELS FROM 24 HOURS AGO, SO  
COULD SEE SHOWERS/STORMS LINGER INTO SATURDAY, WITH ADDITIONAL LIGHT  
SHOWERS POSSIBLE SUNDAY AS A TRAILING WAVE SWINGS THROUGH THE MAIN  
UPPER TROUGH. UPPER RIDGING SHOULD BRING A DRIER PERIOD BACK TO THE  
REGION EARLY NEXT WEEK WITH TEMPERATURES NEAR SEASONAL NORMALS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)  
ISSUED AT 1222 PM CDT TUE SEP 17 2019  
 
VFR THROUGH THE PERIOD. SCATTERED THUNDERSTORMS WILL BE POSSIBLE  
FROM ROUGHLY 6Z TO 14Z ALONG AND EAST OF INTERSTATE 29. CONFIDENCE  
A LITTLE LOW ON TIMING AND COVERGE SO WILL NOT BE A MENTION IN THE  
TAF FORECAST.  
 

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

 
 

 
 
SHORT TERM...JH  
LONG TERM...JH  
AVIATION...08  
 
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