388  
FXUS63 KUNR 251111  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
511 AM MDT MON OCT 25 2021  
   
DISCUSSION
 
(TODAY THROUGH SUNDAY)  
ISSUED AT 206 AM MDT MON OCT 25 2021  
 
DEEP WESTERN CONUS UPPER TROUGH WILL BEGIN TO CROSS THE ROCKIES  
TODAY, SHIFTING THE LEE SIDE TROUGH EAST AND BRINGING WARM CONDS  
TO MUCH OF THE FA. FLOW HAS RESPONDED TO THE ONGOING PRESSURE  
FALLS, WITH GUSTY SE WINDS DEVELOPING OVER THE REGION. POCKET OF  
LL MOISTURE HAS ADVECTED BACK WEST AND INTERSECTED HIGHER TERRAIN,  
LEADING TO DENSE FOG OVER PORTIONS OF WEST CENTRAL AND NW SD.  
HIRES MODELS DO INDICATE THAT DRY SW FLOW ALOFT WILL BEGIN TO  
ERODE THE WESTERN PORTION OF THIS FOG BANK OVERNIGHT, WITH FOG  
EXPECTED TO RETREAT WEST-EAST. DID OPT FOR A DENSE FOG ADV THROUGH  
12Z GIVEN CURRENT OBS AND EXPECTED EVOLUTION OF FOG. WILL RE-  
ASSESS THROUGH THE NIGHT. WAA WILL SPREAD EAST TODAY PER SW ALOFT,  
SUPPORTING A WARM DAY FOR THE SW HALF OF THE FA. HIGHS WILL HINGE  
ON THE DETAILS OF THE LL FLOW AS WELL AS THE EROSION OF  
FOG/STRATUS. DID INCREASE HIGHS OVER SW SD GIVEN HIRES MODEL  
TRENDS. BREEZY SE WINDS WILL INCREASE THROUGH THE DAY, ESP OVER  
PORTIONS OF NW SD WHERE NEAR WIND ADV SPEEDS COULD DEVELOP. DEEP  
WESTERN UPPER TROUGH WILL SHIFT EAST, WITH THE NORTHERN EDGE OF  
THIS SYSTEM SUPPORTING A GOOD CHANCE FOR SHOWERS TUE INTO WED,  
ALONG WITH A PERIOD OF BREEZY NW WINDS, AS THE ASSOCIATED COLD  
FRONT ADVECTS INTO THE REGION TUE MORNING. WARM THERMAL PROFILES  
WILL SUPPORT ALL RAIN WITH THIS SYSTEM, EXCEPT PERHAPS THE HIGHEST  
PORTIONS OF THE BLACK HILLS WHERE SOME SNOW MAY MIX IN LATER TUES  
AFTERNOON AND EVENING. ANOTHER WEAKER COOL FRONT LOOKS TO ARRIVE  
WED NIGHT INTO THUR, WITH NO PRECIP EXPECTED WITH THIS SYSTEM.  
THIS WILL SUPPORT SLIGHT COOLER BUT STILL MILD TEMPS THUR ALONG  
WITH BREEZY NW WINDS. MEAN RIDGING WILL THEN PREVAIL FRI/SAT WITH  
DRY WEATHER AND AVERAGE TO SLIGHTLY ABOVE AVERAGE TEMPS BEFORE A  
STRONG COLD FRONT CROSSES THE PLAINS SUNDAY, SUPPORTING MUCH  
COOLER WEATHER AND MAYBE SOME CHANCES FOR LIGHT SNOW.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 509 AM MDT MON OCT 25 2021  
 
LOW STRATUS CLOUDS AND DENSE FOG WILL PERSIST ACROSS MUCH OF THE  
WESTERN SD PLAINS THIS MORNING. CIGS/VSBY WILL REMAIN IFR/LIFR  
THROUGH AROUND 14-18Z, BEFORE IMPROVING TO VFR. NE WY WILL REMAIN  
VFR THROUGH THE FORECAST PERIOD, WITH GUSTY SOUTHERLY WINDS  
PERSISTING ACROSS NE WY AND WESTERN SD.  
 

 
   
UNR WATCHES/WARNINGS/ADVISORIES
 
 
SD...DENSE FOG ADVISORY UNTIL 9 AM MDT THIS MORNING FOR SDZ001-002-  
012-013-026-030-031-072-073.  
 
WY...DENSE FOG ADVISORY UNTIL 9 AM MDT THIS MORNING FOR WYZ071.  
 

 
 

 
 
DISCUSSION...JC  
AVIATION...EAGAN  
 
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