424  
FXUS63 KFSD 211129  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
529 AM CST MON JAN 21 2019  
   
SHORT TERM
 
(TODAY THROUGH TUESDAY)  
ISSUED AT 308 AM CST MON JAN 21 2019  
 
EARLY THIS MORNING, WE'RE CONTINUING TO WATCH A NARROW BURST OF WARM  
ADVECTION SNOWS MOVE NORTHEAST ACROSS THE CWA. PERIODS OF 1-3 MILE  
SNOWS HAVE BEEN REPORTED WITH THIS BAND, AND IT WILL LIKELY BRING  
ANYWHERE FROM A DUSTING TO 1.5" OF SNOW TO PORTIONS OF THE CWA.  
HIGHEST SNOW TOTALS MAY BE FOUND ALONG THE HIGHWAY 14 CORRIDOR.  
 
OTHERWISE, BIGGEST CONCERN IN THE SHORT TERM PORTIONS OF THE  
FORECAST FOCUSES ON PRECIPITATION CHANCES LATER TODAY THROUGH  
TUESDAY. MODEL GUIDANCE STILL NOT IN GREAT AGREEMENT WITH THE  
PASSAGE OF A SHORTWAVE TROUGH THROUGH THE PLAINS TONIGHT AND  
TUESDAY. GFS/EC/CMC ALL MUCH STRONGER WITH THE MID-LEVEL WAVE  
MOVING ACROSS NEBRASKA AND INTO IOWA TUESDAY MORNING. NAM IS A BIT  
OF AN OUTLIER WITH THIS UPCOMING SYSTEM, BUT DOES SUGGEST A FEW  
AREAS WORTH MONITORING.  
 
AS WEAK LOW LEVEL WARM ADVECTION SPREADS NORTHWARD LATER THIS  
AFTERNOON AND EVENING, WE'LL BEGIN TO SEE THE DEVELOPMENT OF VERY  
LIGHT SNOW OR FREEZING DRIZZLE AHEAD OF AN INVERTED TROUGH  
STRETCHING NORTHWARD ACROSS CENTRAL NEBRASKA AND EAST CENTRAL SOUTH  
DAKOTA. SOUNDINGS SUGGEST THE GREATEST RISK FOR IMPACTFUL FREEZING  
DRIZZLE MAY FORM ALONG THE MISSOURI RIVER, WITH PROBABILITIES  
TRENDING LOWER TOWARDS I-90 AND THEN HIGHWAY 14.  
 
TO THE WEST, A MID-LEVEL BAND OF FRONTOGENESIS WILL AID IN  
DEVELOPING A LINEAR BAND OF SNOW ACROSS NORTHWEST AND CENTRAL  
SOUTH DAKOTA AFTER MIDNIGHT. THIS BAND OF SNOW WILL SLOWLY CREEP  
EASTWARD, ARRIVING IN OUR WESTERN ZONES BY DAYBREAK. WHERE  
UNCERTAINTY BUILDS IN THE FORECAST IS WITH THE PROGRESSION OF  
POTENTIAL INTENSIFICATION OF A MID-LEVEL VORTICITY MAXIMUM  
EJECTING OUT OF EASTERN COLORADO PRIOR TO DAYBREAK TUESDAY.  
EC/GFS/CMC ALL INDICATING THIS WAVE DEEPENS SUFFICIENTLY TO  
ENHANCE LIFT AND PRODUCE A NEW AREA OF FRONTAL BANDING IN AREAS  
FROM YANKTON TO SIOUX CITY AND SPENCER TUESDAY MORNING, WITH THE  
WESTERN BAND QUICKLY DECAYING AFTER DAYBREAK. THIS AREA OF SNOW  
WOULD THEN TRAVERSE ACROSS THE SOUTHEASTERN THIRD OF THE CWA  
THROUGH THE AFTERNOON HOURS.  
 
ACCUMULATION POTENTIAL: WHILE THERE MAY BE A BROAD AREA OF LIGHT  
SNOW ACROSS THE ENTIRE REGION (DUSTING - 2"), FEEL THERE COULD BE  
TWO DISTINCT AREAS OF SLIGHTLY MORE ENHANCED SNOWFALLS. FIRST AREA  
ASSOCIATED WITH INITIAL BANDING THROUGH CENTRAL SD AND INTO THE  
WESTERN THIRD OF THE CWA, AND A SECOND ENHANCED AREA ASSOCIATED WITH  
THE SECONDARY FRONTOGENESIS ACROSS NW IOWA AND NE NEBRASKA. SNOW  
AMOUNTS IN THESE ENHANCED AREAS COULD APPROACH 2-5". AS FAR AS  
ICING IS CONCERNED, MOST AREAS SHOULD REMAIN WITH A GLAZE. AN AREA  
TO WATCH WOULD BE FROM SIOUX CITY TO STORM LAKE AND SPENCER WHERE  
THERE COULD BE SOME POTENTIAL OF A CHANGE FROM FREEZING DRIZZLE  
TO CONVECTIVE FREEZING RAIN.  
 
HAZARDS: A DIFFICULT APPROACH TO HEADLINES, GIVEN MOST AREAS WILL  
SEE LIGHT SNOWS, BUT REMAINING UNDER ADVISORY CRITERIA. AT THIS  
POINT, FEEL MOST CONFIDENT ISSUING AN ADVISORY BASED ON THE  
COMBINATION OF FREEZING DRIZZLE AND LIGHT SNOW POTENTIAL, SEGMENTING  
AREAS OF NW IOWA WHERE TOTALS COULD BE SLIGHTLY HIGHER IF  
ENHANCED BANDING TAKES PLACE TUESDAY. THAT SAID, TRAVEL EVEN  
OUTSIDE ANY ADVISORY MAY BE IMPACTED FOR AN EXTENDED PERIOD GIVEN  
THE PROLONGED NATURE OF THE LIGHT SNOW.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 308 AM CST MON JAN 21 2019  
 
TUESDAY NIGHT: TEMPERATURES SHOULD FALL QUICKLY TUESDAY NIGHT, AS  
LIGHT WINDS AND SURFACE RIDGING MOVE THROUGH.  
 
WEDNESDAY: WARM ADVECTION AND A WEST TO SOUTHWEST SURFACE WIND WILL  
ALLOW TEMPERATURES TO WARM INTO THE 20S AGAIN ON WEDNESDAY. WE  
SHOULD SEE AN INCREASE IN CLOUD COVER AS WELL.  
 
WEDNESDAY NIGHT AND THURSDAY: A PERIOD OF CONCERN FOR THE MIDDLE OF  
THE WEEK, AS MODELS ARE ALL INDICATING AN ARCTIC FRONT WILL BLAST  
THROUGH THE REGION BY DAYBREAK THURSDAY. A BURST OF LIGHT TO  
MODERATE SNOW WILL ACCOMPANY THIS FRONT, AND COULD PRODUCE A QUICK 1-  
2" OF SNOW. THE BIGGEST CONCERN THOUGH WILL BE WITH WINDS. BEHIND  
THE ARCTIC FRONT, SOUNDINGS INDICATE NEARLY 40 KNOTS OF FLOW AT THE  
TOP OF THE MIXED LAYER THURSDAY MORNING. GIVEN THE VERY FLUFFY SNOW  
OVER MUCH OF THE AREA, SIGNIFICANT BLOWING AND DRIFTING OF THE SNOW  
COULD TAKE PLACE THROUGH DAY. IN OPEN AREAS, VISIBILITY COULD BE  
SIGNIFICANTLY IMPAIRED.  
 
FRIDAY-SUNDAY: AS A LARGE UPPER TROUGH BECOMES ESTABLISHED OVER THE  
EASTERN HALF OF THE CONUS, THE CWA WILL BE STUCK IN THE MORE ACTIVE  
SECTOR OF THE TROUGH, DEALING WITH SYSTEMS MOVING THROUGH THE  
NORTHWEST FLOW NEARLY EVERY OTHER DAY. THESE SYSTEM WILL ALSO  
BRING A PARADE OF COLD FRONTS ACROSS THE REGION THROUGH NEXT  
WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 527 AM CST MON JAN 21 2019  
 
MVFR TO IFR CEILINGS THROUGH THE DAYTIME HOURS TODAY. GUSTY WINDS  
WILL CONTINUE AT ALL TERMINALS.  
 
WILL WATCH FOR DEVELOPMENT OF LIGHT FREEZING DRIZZLE OR LIGHT SNOW  
THIS EVENING. FIRST IMPACTING SIOUX CITY AND THEN SIOUX FALLS.  
SOUNDINGS SUPPORT A PROLONGED PERIOD OF LIGHT FREEZING  
PRECIPITATION AT SIOUX CITY, WITH BETTER CHANCES FOR LIGHT SNOW IN  
SIOUX FALLS AND HURON OVERNIGHT. VISIBILITY MAY FALL UNDER 3 MILES  
AT TIMES, WITH LIGHT SNOW SPREADING IN MOST PLACES BY DAYBREAK  
TUESDAY.  
 

 
   
FSD WATCHES/WARNINGS/ADVISORIES
 
 
SD...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST  
TUESDAY FOR SDZ050-063>071.  
 
MN...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST  
TUESDAY FOR MNZ081-089-090.  
 
IA...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST  
TUESDAY FOR IAZ001-002-012.  
 
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT CST  
TUESDAY NIGHT FOR IAZ003-013-014-020>022-031-032.  
 
NE...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST  
TUESDAY FOR NEZ013.  
 
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT CST  
TUESDAY NIGHT FOR NEZ014.  
 

 
 

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