079  
FXUS63 KFSD 282328  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
628 PM CDT TUE MAR 28 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH WEDNESDAY)  
ISSUED AT 331 PM CDT TUE MAR 28 2017  
 
SHOWERS LOCATED OVER WESTERN SD THIS AFTERNOON ARE EXPECTED TO  
REMAIN MAINLY WEST OF OUR CWA THROUGH THE EARLY EVENING. THIS IN  
PART DUE TO A DRY EASTERLY LOW LEVEL FLOW KEEPING MOISTURE AT BAY.  
OTHERWISE, A SHORTWAVE WILL EJECT NORTHWARD OUT AHEAD OF THE LARGE  
UPPER LEVEL LOW OVER EASTERN NM/WESTERN TX OVERNIGHT, LEADING TO AN  
INCREASING CHANCE OF RAIN THROUGH THE MISSOURI RIVER VALLEY. DRY AIR  
WILL REMAIN ENTRENCHED BACK TO THE NORTH AND EAST, AND TIGHTENED UP  
THE POP GRADIENT OVER THOSE AREAS OVERNIGHT. SKIES WILL BE CLOUDY  
TONIGHT, AND TEMPERATURES WILL BE MILDER WITH LOWS IN THE UPPER 30S  
TO LOWER 40S.  
 
THE AFOREMENTIONED UPPER LEVEL LOW DRIFTS INTO THE CENTRAL PLAINS ON  
WEDNESDAY. STRONGEST FORCING, IN THE WAY OF MIDLEVEL ISENTROPIC LIFT  
AND FRONTOGENESIS WILL BE LOCATED ACROSS OUR SOUTHEAST, SO HAVE  
HIGHEST POPS THROUGH THE LOWER MO RIVER VALLEY/NORTHWESTERN IA/AND  
PORTIONS OF OUR LOWER MN ZONES. AGAIN, TIGHTENED UP THE POP GRADIENT  
BACK TO THE NORTH AND WEST WHERE IT LOOKS LIKE DRY AIR WILL WIN OUT.  
WITH THE CLOUDS AND SHOWER IT WILL BE GENERALLY COOLER ON WEDNESDAY,  
WITH HIGHS IN THE UPPER 40S OVER NORTHWESTERN IA TO THE MID 50S  
THROUGH THE CHAMBERLAIN TO HURON CORRIDOR.  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH TUESDAY)  
ISSUED AT 331 PM CDT TUE MAR 28 2017  
 
UPPER AND SURFACE LOW PRESSURE WILL CONTINUE TO TRACK ACROSS THE  
CENTRAL PLAINS WEDNESDAY NIGHT AND THURSDAY. THE LIMITING  
STREAMLINES AT 850-800MB PRETTY MUCH TELL THE WHOLE STORY BY THESE  
TWO PERIODS. WEAK HIGH PRESSURE DEVELOPS NORTH OF THIS LOW IN  
MINNESOTA AND NOSES BACK INTO OUR FORECAST AREA, THEREFORE THE  
TRAJECTORY OF THE STREAMLINES IS FAIRLY DRY. THE ONLY HOOKUP WITH  
THE CENTRAL PLAINS LOW ENCOMPASSES OUR SOUTHEAST ZONES IN NORTHWEST  
IA, WITH RAPIDLY DECREASING POPS HEADING NORTH AND NORTHWEST OF  
THERE. SUPERBLEND POPS DISPLAYED TOO BROAD OF A GRADIENT WEDNESDAY  
NIGHT AND THURSDAY, SO TIGHTENED THE GRADIENT FROM NORTHWEST TO  
SOUTHEAST BY FOLLOWING THE ECMWF AND GFS. SUPERBLEND WAS INFLUENCED  
BY THE NAM WHICH IS LIKELY A BIT TOO FAR NORTH WITH ITS QPF OUTPUT  
GIVEN THE AMOUNT OF DRY AIR WHICH IS STREAMING INTO THE LOWER LAYERS  
FROM THE EAST. AFTER NON EVENTFUL LOWS WEDNESDAY NIGHT, THE  
ATMOSPHERE MIXES TO ABOUT 900MB ON THURSDAY PRODUCING HIGHS OF 45 TO  
50 ALONG AND EAST OF I 29, AND IN THE 50S WEST OF I 29.  
 
AFTER THAT, WE HAVE A VERY PERSISTENT FLOW OF EAST TO SOUTHEAST  
WINDS IN OUR AREA DAY AFTER DAY WITH HIGH PRESSURE IN THE NORTHERN  
MS VALLEY AND GREAT LAKES AREA, WHICH IS AN EXTENSION OF A VERY  
LARGE HIGH PRESSURE SYSTEM OVER THE HUDSON BAY. THE WIND SPEEDS ARE  
NOT VERY STRONG EITHER WHICH WILL KEEP FIRE WEATHER CONCERNS MUTED  
OVER THE NEXT SEVERAL DAYS AT LEAST. ANOTHER STRONG LOW TRACKS  
ACROSS THE CENTRAL AND SOUTHERN PLAINS ONCE AGAIN THIS WEEKEND,  
WHICH WILL PRODUCE CHANCE POPS MAINLY OVER NORTHWEST IA SATURDAY  
AFTERNOON THROUGH SUNDAY. THE WAY IT LOOKS NOW, ONLY LIGHT AMOUNTS  
OF RAIN ARE POSSIBLE IN OUR SOUTHEAST ZONES BECAUSE THE TRAJECTORY  
OF THE STREAMLINES ARE NOT FAVORABLE FOR DEEP MOISTURE.  
INTERESTINGLY, THIS LOW THEN STRENGTHENS TO THE SOUTHEAST OF THIS  
REGION AND THERE IS SOME AGREEMENT IN THAT BETWEEN THE DETERMINISTIC  
SOLUTIONS OF THE GFS AND ECMWF. THEREFORE AT THIS TIME, THERE IS  
DECENT CHANCES OF WIDESPREAD LIGHT RAINFALL AT THE TAIL END OF THE  
EXTENDED PERIOD NEXT TUESDAY. THERE IS ALSO AGREEMENT IN CHILLY  
850MB TEMPERATURES BEYOND THE EXTENDED FORECAST LATER NEXT WEEK, SO  
SOMETHING TO WATCH FOR.  
 
FRIDAY ONWARD, THERE WILL BE A LOT OF 50S FOR HIGHS. NEXT TUESDAY,  
THERE COULD BE AN ERROR OF BEING TOO WARM IF THE AFOREMENTIONED  
STRENGTHENING LOW PANS OUT WHICH WILL DRAIN DOWN COLD AIR FROM THE  
NORTHEAST, ESPECIALLY IF IT RAINS.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)  
ISSUED AT 627 PM CDT TUE MAR 28 2017  
 
VFR CONDITIONS EXPECTED THROUGH THIS EVENING, THEN RAIN WILL  
DEVELOP THROUGH THE MISSOURI RIVER CORRIDOR AFTER 06Z TONIGHT.  
CEILINGS WILL LOWER INTO THE MVFR RANGE WITH THIS ACTIVITY. RAIN  
CHANCES WILL CONTINUE OVER THAT AREA THROUGH WEDNESDAY AFTERNOON,  
WITH THE BEST POTENTIAL FOR LOW CLOUDS AND RAIN REMAINING SOUTH OF  
I-90.  
 

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

 
 

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