984  
FXUS63 KFSD 221718  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
1218 PM CDT FRI OCT 22 2021  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 305 AM CDT FRI OCT 22 2021  
 
LATEST WATER VAPOR LOOP SHOWS A WELL DEFINED WAVE MOVING INTO  
WESTERN ND WITH A FAIRLY STRONG UPPER LEVEL JET DIVING INTO CENTRAL  
AND EASTERN SD. THIS IS PRODUCING WEAK RETURNS ON RADAR OVER CENTRAL  
AND NORTHERN SD EARLY THIS MORNING, BUT MODEL SOUNDINGS ARE SHOWING  
A BIT OF A STRUGGLE TO SATURATE IN THE LOWER LEVELS. HOWEVER  
COMPARED TO YESTERDAYS MODEL RUNS THE LOWER LEVELS ARE NOT NEARLY AS  
DRY, SO PRECIPITATION CHANCES WILL BE A BIT HIGHER THAN PREVIOUSLY  
THOUGHT. FORCING IN THE DENDRITIC LAYER MAXIMIZES ACROSS THE AREA,  
ESPECIALLY SOUTHEAST SD, THIS MORNING. FOR THE MOST PART IT APPEARS  
THAT RAIN SHOWERS WILL BE THE PREDOMINANT WEATHER TYPE, BUT A FEW  
SNOWFLAKES ARE NOT IMPOSSIBLE. THE WET BULB TEMPERATURE NOT QUITE  
COLD ENOUGH TO SUPPORT SNOW WHERE THE STRONGEST FORCING IS, BUT  
PARTS OF SOUTHWEST MN WOULD HAVE THE BETTER CHANCE IF PRECIPITATION  
ENDS UP BEING A LITTLE FARTHER NORTH AND EARLY THIS MORNING IN PARTS  
OF SOUTHEAST SD BEFORE A TOUCH OF WARMING DEVELOPS. MOST OF THE  
PRECIPITATION WILL BE OUT OF THE AREA BY MORNING, POSSIBLY LINGERING  
IN NORTHWEST IA THROUGH EARLY AFTERNOON. COOL EASTERLY FLOW IN THE  
WAKE OF THIS WAVE WILL LEAVE THE AREA WITH HIGHS AGAIN IN THE UPPER  
40S TO MID 50S. BUT WITH LIGHTER WINDS THIS WILL NOT FEEL TOO BAD.  
 
MID AND UPPER LEVEL RIDGING WILL BUILD ACROSS THE AREA TONIGHT SO  
EXPECT EAST TO SOUTHEAST FLOW TO SLOWLY INCREASE. STILL SOME  
QUESTION ON LOWS BUT SHOULD SEE QUITE A FEW AREAS AROUND OR A COUPLE  
OF DEGREES BELOW FREEZING, ESPECIALLY EAST OF THE JAMES RIVER. THIS  
SHOULD ALLOW SOME FROST TO DEVELOP. SUSPECT THAT THERE COULD BE A  
LITTLE FOG AS WELL WITH A RELATIVELY WET GROUND AND LIGHT WINDS.  
   
LONG TERM
 
(SATURDAY THROUGH THURSDAY)  
ISSUED AT 305 AM CDT FRI OCT 22 2021  
 
AS A STRONG UPPER LEVEL TROUGH DEVELOPS OVER THE WEST COAST AND  
SHIFTS EAST INTO THE ROCKIES ON SATURDAY, SOUTHEAST FLOW WILL  
INCREASE WITH MARGINALLY BREEZY CONDITIONS EXPECTED. CLOUDS WILL  
INCREASE LATE IN THE DAY AS THE TROUGH APPROACHES THE WESTERN HIGH  
PLAINS. THE LOW LEVEL THERMAL FIELD NOT OVERLY WARM, BUT SHOULD  
SUPPORT MOST LOCATIONS REACHING THE LOW TO MID 50S. ALL IN ALL A BIT  
OF A CHILLY DAY.  
 
LATE SATURDAY NIGHT INTO SUNDAY A STRONG TROUGH WILL SPREAD ACROSS  
THE PLAINS WITH WARM ADVECTION INCREASING SIGNIFICANTLY. THE MAIN  
CHALLENGE FOR PRECIPITATION IN THE AREA WILL BE THE POTENTIAL FOR  
CONVECTION SOUTH OF INTERSTATE 80 REDIRECTING THE STRONG LOW TO MID  
LEVEL MOISTURE ADVECTION. WHILE THIS MAY BE A PROBLEM STILL BELIEVE  
THAT MOST LOCATIONS ALONG AND EAST OF INTERSTATE 29 WILL SEE SOME  
RAINFALL. THE GFS IS A BIT OF A NORTHERN OUTLIER WHILE THE ECMWF AND  
CANADIAN SUPPORT A BIT MORE OF A SOUTHERN TRACK. ALL MODELS FAIRLY  
AGREEABLE ON A STRONG DEEPENING LOW PRESSURE WHICH SHOULD ALLOW FOR  
SOME EASTERLY WRAP AROUND IN THE LOW TO MID LEVELS. STILL APPEARS TO  
BE THE CHANCE FOR SOME THUNDER IN MAINLY NORTHWEST IA BUT NOT  
ANTICIPATING SEVERE. LOWS WILL BE MORE MILD SUNDAY MORNING, MOSTLY  
UPPER 30S TO LOWER 40S, BUT DAYTIME TEMPERATURES LIKELY TO NOT RISE  
MUCH SO LOWERED HIGHS A TOUCH, AND ONLY EXPECT ABOUT A 5 TO 8 DEGREE  
DIURNAL RISE.  
 
MONDAY INTO MONDAY NIGHT WILL SEE UPPER LEVEL RIDGING BRING DRY  
CONDITIONS AS THE NEXT STRONG PIECE OF ENERGY MOVES INTO THE  
ROCKIES. HIGHS WILL BE ON THE COOL SIDE, MOSTLY UPPER 40S TO LOWER  
50S, WITH TUESDAY MORNING LOWS IN THE MID 30S TO LOWER 40S. IF THE  
TIMING PANS OUT COULD SEE SOME DRIZZLE DEVELOP MONDAY NIGHT INTO  
TUESDAY MORNING AS THE DENDRITIC LAYER APPEARS TOO DRY TO SUPPORT  
RAIN, BUT A POTENTIALLY DEEP SURFACE TO 4-5 KFT SATURATED LAYER  
COULD DEVELOP.  
 
TUESDAY INTO WEDNESDAY MORNING WILL BE A GOOD CHANCE FOR RAINFALL AS  
THE TROUGH MOVES THROUGH. CONFIDENCE NOT OVERLY HIGH AS THE MODELS  
ARE TRYING TO RESOLVE WHAT ALL OF THIS ENERGY MOVING ON TO THE WEST  
COAST IS GOING TO DO, BUT IF THE WAVE DOES MOVE OUT OF THE AREA  
WEDNESDAY MORNING IT APPEARS THAT IT WILL BE A BIT WINDY WEDNESDAY  
AND THURSDAY WITH NEAR NORMAL TEMPERATURES.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1214 PM CDT FRI OCT 22 2021  
 
SHOWERS CONTINUE SLIDING TO THE SOUTHEAST THIS AFTERNOON ACROSS  
FAR SOUTHEASTERN SD, NORTHEASTERN NE, AND NORTHWESTERN IA. EXPECT  
THESE TO CONTINUE TO MOVE OUT OF THE AREA BY 20Z, WITH CEILINGS  
AND VISIBILITY IMPROVING FROM MVFR TO VFR AS WELL.  
 
SKIES ARE CLEARING BEHIND THIS PRECIPITATION, LEADING TO VFR  
CONDITIONS. VFR IS EXPECTED THROUGH THE REST OF THE PERIOD. SOME  
MODEL GUIDANCE LATE THIS MORNING/EARLY THIS AFTERNOON CONTINUES TO  
HINT AT FOG/STRATUS DEVELOPMENT AGAIN TONIGHT; HOWEVER, CONFIDENCE  
IS TOO LOW AT THIS TIME TO INCLUDE AT ANY SITE.  
 

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

 
 

 
 
SHORT TERM...08  
LONG TERM...08  
AVIATION...SG  
 
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