700  
FXUS63 KUNR 210938  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
238 AM MST TUE NOV 21 2017  
   
DISCUSSION
 
(TODAY THROUGH MONDAY)  
ISSUED AT 216 AM MST TUE NOV 21 2017  
 
WATER VAPOR SHOWS TROF AXIS MOVING FROM THE DAKOTAS INTO THE UPPER  
MIDWEST, AND UPPER RIDGE OVER THE WESTERN CONUS. SHORT WAVE AT THE  
BASE OF TROF RESULTING IN BAND OF LIGHT SNOW SHIFTING SOUTHWARD  
THROUGH THE CWFA. AT THE SURFACE, HIGH PRESSURE BUILDING INTO THE  
NORTHERN PLAINS EARLY THIS MORNING WITH BRISK NORTHWEST WINDS AND  
MUCH COLDER TEMPS.  
 
LIGHT SNOW WILL QUICKLY SHIFT SOUTH OF THE REGION AROUND DAYBREAK,  
WITH CLEARING SKIES AS MUCH DRIER AIR WORKS IN FROM THE NORTH.  
TEMPS TODAY WILL BE MUCH COLDER THAN YESTERDAY, BUT STILL VERY  
CLOSE TO AVERAGE. GUSTY NORTHWEST WINDS WILL DIMINISH LATER THIS  
AFTERNOON WITH CANADIAN HIGH MOVING INTO THE CENTRAL DAKOTAS.  
 
WARM ADVECTION WILL RETURN IN EARNEST TONIGHT AS LEE TROF QUICKLY  
ADVANCES INTO EASTERN MT/WY. MUCH WARMER TEMPS AND DRY CONDITIONS  
THEN EXPECTED WEDNESDAY AND THANKSGIVING AS UPPER RIDGE AXIS  
SHIFTS EASTWARD ACROSS THE NORTHERN ROCKIES/PLAINS. TEMPS WELL  
INTO THE 60S EXPECTED WEDNESDAY, WITH SOME LOWER 70S ON  
THANKSGIVING DAY. WILL PROBABLY SEE SOME RECORD HIGHS SET ON  
THANKSGIVING.  
 
NEXT UPPER TROF WILL ARRIVE ON FRIDAY, BRINGING GUSTY NORTHWEST  
WINDS AND COOLER TEMPS, ALONG WITH SOME LIGHT PCPN. HAVE TRENDED  
WINDS UPWARD FROM GUIDANCE GIVE THE STRENGTH OF UPPER TROF AND  
COLD ADVECTION.  
 
UPPER RIDGE THEN REBUILDS FOR THE WEEKEND INTO EARLY NEXT WEEK  
FOR MORE DRY AND VERY MILD CONDITIONS. WOULD NOT BE SURPRISED TO  
SEE MORE RECORD HIGHS BY NEXT SUNDAY OR MONDAY AS THERMAL RIDGE  
AXIS PASSES OVERHEAD.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)  
ISSUED AT 1033 PM MST MON NOV 20 2017  
 
VFR CONDITIONS CONTINUE ACROSS TAF SITES FOR NOW. HOWEVER, IFR  
CIGS AND/OR VSBYS ARE ONGOING ACROSS NORTHEAST WY AND THE NORTHERN  
BLACK HILLS AND SHOULD CONTINUE THROUGH MOST OF THE OVERNIGHT.  
EXPECT GCC TO FALL TO MVFR BY 06Z AS LOWER CIGS UPSTREAM  
APPROACH. SHOULD ALSO BEGIN TO SEE SUFFICIENT MOISTENING FOR SNOW  
TO REACH THE GROUND AROUND THIS TIME. NOT CURRENTLY EXPECTING IFR  
CIGS/VSBYS AT GCC, BUT IT IS PLAUSIBLE THAT IFR CONDITIONS COULD  
BRIEFLY OCCUR THROUGH 10Z. SNOW SHOULD END BY 12Z AS MID AND UPPER  
LEVELS DRY RAPIDLY, BUT LOW CIGS WILL CONTINUE INTO TUESDAY  
AFTERNOON. WESTERN SD (OUTSIDE OF THE BLACK HILLS) MAY TEMPORARILY  
DROP TO MVFR CIGS/VSBYS WITH LIGHT RAIN/SNOW SHOWERS TONIGHT, BUT  
CONDITIONS SHOULD IMPROVE TO VFR FOR MOST OF TUESDAY.  
 

 
   
UNR WATCHES/WARNINGS/ADVISORIES
 
 
SD...NONE.  
WY...NONE.  

 
 

 
 
DISCUSSION...JOHNSON  
AVIATION...CALDERON  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SD Page
The Nexlab WY Page Main Text Page