351  
FXUS63 KFSD 272324  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
624 PM CDT MON MAR 27 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY)  
ISSUED AT 302 PM CDT MON MAR 27 2017  
 
HIGH PRESSURE WILL BE THE DOMINANT FEATURE TONIGHT AS IT EXTENDS  
FROM SOUTH CENTRAL CANADA THROUGH THE EASTERN PLAINS. WINDS WILL BE  
LIGHT, AND WILL SHIFT TO AN EAST TO SOUTHEAST DIRECTION AS THE NIGHT  
PROGRESSES. THERE ARE TWO THINGS TO WATCH FOR, FIRST IS WHETHER  
CLOUDS WILL ERODE HEADING DEEPER INTO NORTHWEST IA. SECOND IS  
ANY FOG FORMATION. IT IS DOUBTFUL WHETHER THE STRATUS WILL  
COMPLETELY ERODE IN MUCH OF NORTHWEST IA. THAT SAID, THE BACK EDGE  
OF THE STRATUS WILL LIKELY DISSIPATE AROUND SUNSET ALONG HIGHWAY 60  
INCLUDING SIOUX CITY LEAVING A MAINLY CLEAR SKY THIS EVENING, WITH  
CLOUD COVER FURTHER EAST AROUND SPENCER AND STORM LAKE. AS THE  
BOUNDARY LAYER FLOW THEN SHIFTS TO THE EAST, AM CONCERNED THAT SOME  
THE STRATUS MAY REFORM OVER THE WESTERN SECTIONS OF NORTHWEST IA  
LATER TONIGHT AS IT BACKS IN FROM THE EAST. THE RAP13 900MB  
RELATIVE HUMIDITY HAS A GOOD HANDLE ON THE CURRENT STRATUS FIELD,  
AND WAS USED FOR THIS SCENARIO LATER TONIGHT AND EARLY TUESDAY.  
 
WITH THE LIGHT WINDS, AREAS OF FOG COULD ONCE AGAIN DEVELOP,  
ESPECIALLY FOR AREAS ALONG THE EDGE OF THE STRATUS FIELD IN OUR  
EASTERN ZONES, THEN EXPANDING INTO THE STRATUS AREAS HEADING INTO  
EARLY TUESDAY. SO SOME FOG COULD ENCOMPASS MANY OF OUR EASTERN ZONES  
BY LATE TONIGHT ESPECIALLY IN TERRAIN DRIVEN AREAS SUCH AS RIVER  
VALLEYS, AND ALSO IN SOUTH CENTRAL SD ALONG THE MO RIVER CORRIDOR  
WITH THE UPSLOPE FLOW IN THAT AREA.  
 
LOWS TONIGHT WILL BE SEASONABLY MILD WITH READINGS IN THE 30S. ANY  
FOG WILL LIKELY BE OF SHALLOW DEPTH AGAIN, BURNING OFF IN THE MID  
MORNING HOURS. BUT DEEPER MOISTURE WILL THEN MOVE INTO OUR AREA  
AHEAD OF THE NEXT UPPER LOW PRODUCING INCREASING CLOUD COVER FROM  
WEST TO EAST. HOWEVER WITH THE CONTINUED EAST TO SOUTHEAST FETCH OF  
LOW LEVEL AIR, THE LOWEST LAYERS MAY REMAIN A BIT DRY FOR MUCH OF  
OUR FORECAST AREA, SO PRECIP CHANCES WILL ERODE IN OUR WESTERN  
ZONES. ONLY HAVE MEASURABLE POPS FOR LIGHT RAINFALL BASICALLY IN  
GREGORY COUNTY IN THE AFTERNOON. HIGHS ON TUESDAY WILL GENERALLY  
RANGE FROM 55 TO 60.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH MONDAY)  
ISSUED AT 302 PM CDT MON MAR 27 2017  
 
WHILE THE PATTERN APPEARS TO BE A FAIRLY BUSY ONE WEDNESDAY THROUGH  
MONDAY MUCH OF THE ACTIVITY SHOULD STAY TO THE SOUTH ACROSS PARTS OF  
NEBRASKA, IOWA, KANSAS AND MISSOURI. AT THIS TIME OUR BETTER CHANCE  
FOR RAINFALL WILL COME TUESDAY NIGHT INTO WEDNESDAY AS LOW PRESSURE  
ALOFT MOVES THROUGH KANSAS INTO ILLINOIS. WHILE A LITTLE THUNDER  
IS NOT IMPOSSIBLE THE THREAT IS TOO LOW TO MENTION. THE BETTER  
CHANCES FOR RAINFALL WILL BE ALONG THE MISSOURI RIVER INTO  
NORTHWEST IOWA WHERE A QUARTER INCH OF RAIN WILL BE POSSIBLE. A  
SERIES OF WAVES MOVES THROUGH AFTER THIS BUT AT THIS TIME THE MAIN  
AFFECTS WILL BE TO THE SOUTH OF THE AREA. NOT TO MENTION SOME  
CONCERN WITH CONSISTENCY IN TIMING AND PLACEMENT OF THIS ENERGY.  
IN GENERAL LOOKING AT ABOVE NORMAL TEMPERATURES, NOT BY A LOT, BUT  
HIGHS IN THE 50S AND LOWS IN THE 30S. THERE ARE SOME HINTS THAT  
READINGS ANOTHER 5 TO 10 DEGREES WARMER WILL BE POSSIBLE BY SUNDAY  
AND MONDAY SO WILL MONITOR THOSE TRENDS THE NEXT FEW DAYS.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)  
ISSUED AT 621 PM CDT MON MAR 27 2017  
 
LOW STRATUS HAS RETREATED THIS AFTERNOON, HOWEVER THERE REMAINS  
SOME CONCERN THAT IT MAY CREEP BACK INTO NORTHWEST IOWA LATER  
TONIGHT INTO TUESDAY MORNING. WITH LIGHT WINDS IN PLACE, THERE  
WILL ALSO BE SOME CONCERN FOR AREAS OF FOG DEVELOPING ALONG AND  
EAST OF THE I-29 CORRIDOR LATE TONIGHT. HAVE MVFR CONDITIONS IN  
THE FSD AND SUX TAFS LATE TONIGHT THROUGH 15Z.  
 

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

 
 

 
 
SHORT TERM...MJ  
LONG TERM...08  
AVIATION...  
 
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