402  
FXUS63 KFSD 172100  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
300 PM CST WED JAN 17 2018  
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY)  
ISSUED AT 300 PM CST WED JAN 17 2018  
 
QUIET WEATHER IN THE SHORT-TERM. CONTINUED WESTERLY FLOW OVER THE  
NEXT 24 H WILL CONTINUE TO BRING WARMER AIR INTO THE AREA. WHILE THE  
FLOW IS NOT PERPENDICULAR TO THE BUFFALO RIDGE, THERE IS A STRONG  
ENOUGH CROSS-RIDGE COMPONENT AS WELL AS STRONG THERMAL INVERSION TO  
KEEP WIND GUSTING OVER 20 MPH THROUGH THURSDAY. WINDS WILL BECOME  
LIGHTER - ESPECIALLY IN VALLEY LOCATIONS - LATER TONIGHT. THIS WILL  
ALLOW LOW TEMPERATURES TO FALL INTO THE TEENS. ON THURSDAY, 925 MB  
TEMPERATURES WILL RANGE FROM 3 TO 10 C. WHILE THERE IS SOME SNOW ON  
THE GROUND, ITS IMPACT WILL NOT REAL SIGNIFICANT - MAYBE KEEP  
TEMPERATURES 3 TO 5 DEGREES COOLER THAN IF IT FULLY MIXED OUT. FOR  
THIS REASON, HAVE RAISED HIGHS INTO THE 40S EVERYWHERE WITH THE  
LOWER 50S IN SOUTH CENTRAL SOUTH DAKOTA.  
   
LONG TERM
 
(THURSDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 300 PM CST WED JAN 17 2018  
 
THE PRIMARY FOCUS IN THE LONG TERM IS THE WARM WEATHER ON FRIDAY  
AND THE POTENTIAL WINTER STORM FOR LATER SUNDAY INTO MONDAY.  
 
ON FRIDAY, A WEAK BOUNDARY IS FORECAST TO MOVE SLOWLY SOUTHWARD  
THROUGH THE AREA. AHEAD OF THE BOUNDARY 925 MB TEMPS ARE AROUND 10 C  
AND THEY ONLY SLOWLY COOL BEHIND THE BOUNDARY. AT LEAST SOME OF THE  
AREA WILL LOSE SNOWCOVER TOMORROW SO THAT MIXING COULD BE MORE  
EFFICIENT. BASED UPON CURRENT SATELLITE PICTURE THAT SEEMS MOST  
LIKELY WEST OF THE JAMES RIVER AND ALSO IN THE MISSOURI VALLEY.  
HOWEVER, THERE COULD ALSO BE MORE CIRRUS AROUND WHICH WOULD LIMIT  
SOLAR HEATING. FOR THIS REASON, LIMITED MIXING TO AROUND 3 C ABOVE  
925 MB TEMPERATURES. THAT STILL RESULTS IN HIGH TEMPERATURES WARMER  
THAN THURSDAY FROM THE MID 40S ALONG THE BUFFALO RIDGE TO THE MID  
50S IN THE MISSOURI VALLEY.  
 
NO SIGNIFICANT COOLING IS EXPECTED BEHIND THE FRONT AS LOWS WILL  
REMAIN IN THE 20S ON FRIDAY NIGHT. DESPITE MORE CLOUDS AND  
NORTHEASTERLY, TEMPERATURES ARE EXPECTED TO REMAIN ABOVE SEASONAL  
NORMALS FROM THE UPPER 30S IN SOUTHWESTERN MINNESOTA TO THE MID 40S  
AROUND YANKTON AND SIOUX CITY.  
 
A MORE SIGNIFICANT SYSTEM MAY IMPACT THE AREA SUNDAY AND MONDAY.  
INITIALLY, WE ARE EXPECTING A 700 MB FRONT TO SET UP OVER THE  
NORTHERN PLAINS AND INTERACT WITH THE ENTRANCE REGION OF AN UPPER  
LEVEL JET NEAR THE CANADIAN BORDER. THE EXACT LOCATION OF THE FRONT  
REMAINS VERY UNCERTAIN AT THIS TIME BUT THE MOST LIKELY AREA WOULD  
BE NORTH OF I90 AND IT COULD EVEN BE NORTH OF HWY 14. THIS WOULD  
BRING LIGHT SNOW FROM LATE SATURDAY NIGHT INTO SUNDAY. A MORE  
SIGNIFICANT UPPER LOW IS THEN EXPECTED TO MOVE NORTHEAST FROM THE  
ROCKIES INTO THE GREAT LAKES. MODEL SOLUTIONS ARE BECOMING MORE  
CERTAIN THAT THIS WILL IMPACT THE CENTRAL PLAINS INTO THE GREAT  
LAKES AND COULD BRING SIGNIFICANT SNOWFALL WITH STRONG WINDS.  
 
BOTH TIMING AND LOCATION REMAIN HIGHLY UNCERTAIN. IN TERMS OF  
TIMING, SNOWFALL COULD OCCUR ANYTIME FROM SUNDAY AFTERNOON INTO  
MONDAY EVENING. CURRENTLY THE GFS IS THE FASTEST SOLUTION - STARTING  
SUNDAY AFTERNOON AND ENDING SOMETIME MONDAY MORNING WHILE THE ECMWF  
AND CANADIAN HAVE THE HEAVIEST SNOWFALL ON MONDAY MORNING ENDING  
MONDAY EVENING. THE LOCATION IS STILL VARYING FROM CENTRAL AND  
NORTHERN IOWA TO AS FAR NORTH AS NORTHEASTERN SOUTH DAKOTA AND  
CENTRAL MINNESOTA. WHAT WE CAN SAY IS CONFIDENCE HAS INCREASED THAT  
MANY AREAS WILL SEE AT LEAST LIGHT SNOWFALL SOMETIME FROM LATE  
SUNDAY AFTERNOON INTO MONDAY MORNING. HOWEVER, WHETHER ANY ONE  
LOCATION WILL SEE HEAVY SNOWFALL REMAINS VERY UNCERTAIN. SO,  
ALTHOUGH BOTH THE 12Z GFS AND ECMWF DO SHOW HEAVY SNOW FOR THE TRI-  
STATE AREA, DO NOT FOCUS ON THE EXACT LOCATION OR AMOUNTS FROM ANY  
ONE MODEL. INSTEAD, BE AWARE THAT A WINTER STORM IS POSSIBLE BUT  
AREAS THAT COULD BE AFFECTED COULD STILL BE SOUTH OF SIOUX CITY AND  
SPENCER OR NORTH OF CHAMBERLAIN, BROOKINGS AND MARSHALL. IT REMAINS  
TOO EARLY TO SAY WITH ANY CONFIDENCE IF ANY ONE LOCATION WILL BE  
IMPACTED.  
 
FOLLOWING THE SYSTEM ON SUNDAY AND MONDAY - NEAR NORMAL TEMPERATURES  
ARE EXPECTED INTO THE MIDDLE OF NEXT WEEK.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 1104 AM CST WED JAN 17 2018  
 
VFR CONDITIONS EXPECTED THROUGH 18Z THURSDAY.  
 

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

 
 

 
 
SHORT TERM...SCHUMACHER  
LONG TERM...SCHUMACHER  
AVIATION...SCHUMACHER  
 
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