948  
FXUS63 KFSD 261108  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
608 AM CDT WED APR 26 2017  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 402 AM CDT WED APR 26 2017  
 
UPPER LEVEL LOW PRESSURE ACROSS NORTHERN SOUTH DAKOTA WILL CONTINUE  
TO WANDER EAST/NORTHEAST TODAY, SLOWLY INTENSIFYING AS IT MOVES INTO  
NORTHERN MINNESOTA BY THURSDAY MORNING. WHILE A BULK OF THE DEEPER  
FORCED PRECIPITATION HAS PULLED EAST OF THE AREA OTHER THAN ACROSS  
PARTS OF SOUTHWEST MN, THERE REMAINS AN ABUNDANCE OF LOW LEVEL  
MOISTURE WHICH CONTINUES TO PRODUCE SPOTTY DRIZZLE ACROSS SOUTHEAST  
SD INTO NORTHWEST IA AT 09Z. FORECAST CONCERNS LINE UP BEHIND  
PRECIPITATION TYPE INTO THE MORNING HOURS, SPECIFICALLY POTENTIAL  
FOR AREAS OF LIGHT FREEZING DRIZZLE TOWARD HIGHWAY 14. BECAUSE OF  
OUR LOCATION SOUTHEAST OF THE UPPER WAVE IN THE LARGER SCALE MID-  
LEVEL DRY SLOT, MOST MODEL THERMAL PROFILES INDICATE THAT SATURATION  
DEPTH DOES APPEAR TO BE AN ISSUE WITH LACK OF ICE PRODUCTION FOR  
MOST AREAS, PERHAPS BRIEFLY REACHING THE THRESHOLD AROUND KHON EARLY  
THIS MORNING. THERE WOULD BE THE CHANCE FOR SOME SPOTTY VERY LIGHT  
ICING NEAR HIGHWAY 14 THROUGH AROUND 14Z AS TEMPS DANCE CLOSE TO  
FREEZING AT THE SURFACE.  
 
DOES LOOK AS IF THERE COULD BE MULTIPLE ATTEMPTS FOR PRECIP IN LOW-  
TO MID-LEVEL DEFORMATION BAND TO WRAP BACK INTO THE HIGHWAY 14  
CORRIDOR DURING THE DAY, FIRST AND PERHAPS MOST AGGRESSIVELY THROUGH  
MID MORNING, BUT LARGER SCALE SUBSIDENCE WILL BE WORKING TO ERODE  
THE SOUTHERN END OF THE AREA AS IT PUSHES SOUTHWARD. ANOTHER  
ATTEMPT WILL BE MADE AROUND EARLY AFTERNOON, BUT BY THIS TIME TEMPS  
NEAR SURFACE WILL BE SOMEWHAT WARMER AND SHOULD SEE MAINLY LIQUID  
PRECIP.  
 
OTHERWISE, THE CYCLONIC ENVIRONMENT PROMISES TO KEEP A LOT OF  
CLOUDINESS IN PLACE ACROSS THE AREA, WITH PERHAPS A FEW BREAKS  
WORKING TOWARD THE WESTERN MISSOURI RIVER LATER IN THE DAY. TEMPS  
WILL MODERATE JUST A BIT TODAY, BUT GENERALLY WARM NO MORE THAN 5-10  
DEGREES FROM CURRENT READINGS.  
 
DESPITE THE CLOUDS AND CONTINUED NORTHERLY WINDS, TEMPERATURES  
TONIGHT DO APPEAR LIKELY TO DROP INTO THE UPPER 20S TO AROUND 30 FOR  
A GOOD PORTION OF THE AREA, BUT UNCERTAINTY LIES WITHIN TWO AREAS -  
1) HOW MANY CLOUDS WILL EITHER LINGER OR WRAPS SOUTHWARD INTO THE  
AREA OVERNIGHT TO IMPACT TEMPERATURE TRENDS, AND 2) IMPACT OF  
CONTINUED WINDS OVERNIGHT, WHICH WILL BECOME LIGHTEST NEAR RIDGE  
AXIS THROUGH CENTRAL SD. AS A RESULT OF THE SECOND, WIDESPREAD FROST  
DOES NOT APPEAR TO BE A VIABLE CONCERN FOR MOST AREAS, WITH  
EXCEPTION OF PERHAPS TOWARD LOWER BRULE AREAS. HOWEVER, IF CLOUDS  
BREAK WITH THE LIGHT WINDS, AN EVEN STRONGER TEMPERATURE FALL WILL  
MAKE FOR A SIGNIFICANT FREEZE AS WELL. A FREEZE WATCH WOULD SEEM TO  
BE THE MOST APPROPRIATE CHOICE AT THIS POINT CONSIDERING VEGETATION  
STATE AND EXPECTED TEMPERATURE/WIND. HOWEVER, THIS WOULD END UP  
BEING A CWA STAND-ALONE AND NOT PREPARED TO DO THIS GIVEN AT LEAST  
SOME UNCERTAINTY ON HOW LONG TEMPS WILL BE NEAR THE MINIMUM. WILL  
HIGHLIGHT THE SUB-FREEZING TEMPERATURES IN THE HWO AND SOCIAL MEDIA,  
FOR MANY AREAS, ESPECIALLY NEAR AND WEST OF I-29, WILL HAVE TO BE  
VERY WARY OF OVERNIGHT TEMPS.  
   
LONG TERM
 
(THURSDAY THROUGH TUESDAY)  
ISSUED AT 402 AM CDT WED APR 26 2017  
 
CERTAINLY THE TRENDS THROUGH THE MEDIUM AND EXTENDED PORTIONS OF THE  
FORECAST CONTINUE TO SHOW COOLER THAN NORMAL TEMPERATURES INTO EARLY  
MAY. THE BIGGEST STORY HOWEVER COULD BE A POTENTIAL STORM FOR THE  
UPCOMING WEEKEND AND IT'S IMPACT ON TEMPERATURES AND PRECIPITATION  
TYPES.  
 
THURSDAY AND FRIDAY CONTINUE TO TREND DRY WITH THE CWA STUCK  
IN BETWEEN TROUGHING OVER THE NORTHERN GREAT LAKES AND A  
SECONDARY OPEN WAVE MOVING THROUGH THE CENTRAL ROCKIES. HIGH  
PRESSURE WILL BE IN CONTROL OF THE LOCAL AREA, WITH THE BEST  
CHANCE FOR PRECIPITATION FOCUSED ACROSS NEBRASKA INTO SOUTHERN  
IOWA. TEMPERATURES WILL REMAIN ON THE COOL SIDE, WITH HIGHS IN THE  
LOWER 50S.  
 
FOCUS THEN TURNS TOWARD ENERGY THAT IS EXPECTED TO DIG INTO THE  
ROCKIES AND PIVOT NORTHEASTWARD THROUGH THE PLAINS AND INTO THE  
GREAT LAKES SUNDAY AND MONDAY. MODELS HAVE TRENDED DEEPER AND  
FURTHER NORTHWEST WITH THIS SYSTEM. WHICH LOOKS TO DEEPEN AS IT  
MOVES BY THE FORECAST AREA ON SUNDAY. OBVIOUSLY ALL KINDS OF MESS  
REGARDING THE THERMAL PROFILE AND EXPECTED WEATHER ELEMENTS THROUGH  
THE EVENT. PRECIPITATION MAY LIKELY BEGIN AS RAIN SATURDAY NIGHT,  
BUT AS THE SYSTEM PIVOTS NORTHWARD, DYNAMICAL COOLING COULD PUSH  
CRITICAL TEMPERATURES DOWNWARD AND MORE FAVORABLE FOR SNOW. AT THAT  
POINT IT BECOMES A MATTER OF THE WARMTH AND DEPTH OF THE SHALLOW  
WARM LAYER AT THE BOUNDARY LAYER TO DETERMINE IF PRECIPITATION WOULD  
FALL AS SNOW, RAIN/SNOW, OR RAIN IN THE AFTERNOON. GENERAL COOLING  
OF THE LOWEST 1000 FT WOULD FAVOR A FULL TRANSITION TO SNOW SUNDAY  
NIGHT. STILL 4-5 DAYS OUT FOR THIS SYSTEM, BUT WILL NEED TO KEEP A  
CLOSE EYE ON CRITICAL ELEMENTS SUCH AS TEMPERATURES. FOR NOW HAVE  
LOWERED TEMPERATURES ON SUNDAY ON AVERAGE OF 5 TO 8 DEGREES AND  
BLENDED IN COLDER CONSRAW GUIDANCE.  
 
LOW CONSISTENCY IN GUIDANCE BEHIND THIS SYSTEM LEADS TO FEW  
MODIFICATIONS TO THE FORECAST.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)  
ISSUED AT 607 AM CDT WED APR 26 2017  
 
WIDESPREAD IFR CONDITIONS WILL GRADUALLY LIFT TO MVFR THIS MORNING,  
WITH AREAS THROUGH THE MISSOURI RIVER VALLEY REACHING VFR DURING  
THE AFTERNOON OR EARLY EVENING. WILL LIKELY GET RENEWED AREA OF  
MVFR CEILINGS SPREADING SOUTHWARD THROUGH THE NIGHT INTO KFSD AND  
KHON. OTHERWISE, A LITTLE LIGHT FREEZING DRIZZLE WILL BE POSSIBLE  
THIS MORNING FOR MAINLY KHON AND EASTWARD TOWARD KBKX AS  
SATURATION INTO ICE BEARING LEVELS WILL BE DIFFICULT TO COME BY,  
EXCEPT PERHAPS FOR A BRIEF TIME AROUND KHON. ADDITIONAL MVFR  
VISIBILITIES IN DRIZZLE WILL REMAIN POSSIBLE MAINLY ALONG AND EAST  
OF I-29 THIS MORNING.  
 

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

 
 

 
 
SHORT TERM...CHAPMAN  
LONG TERM...DUX  
AVIATION...CHAPMAN  
 
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