510  
FXUS63 KUNR 210440  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
1040 PM MDT FRI APR 20 2018  
   
DISCUSSION
 
(THIS EVENING THROUGH FRIDAY)  
ISSUED AT 155 PM MDT FRI APR 20 2018  
 
THE UPPER LOW SPINS OVER THE FOUR CORNERS REGION, PUSHING RAIN  
NORTHWARD INTO THE NORTHERN PLAINS. RADAR SHOWS RAIN EXPANDING  
ACROSS SOUTHERN SD. SOMEWHAT TIGHT PRESSURE GRADIENT EXISTS  
BETWEEN THE SURFACE HIGH TO THE EAST AND LOW TO THE WEST, CREATING  
SOME BREEZY SOUTHERLY WINDS THIS AFTERNOON. TEMPERATURES ARE IN  
THE 40S AND LOWER 50S.  
 
RAIN WILL CONTINUE TONIGHT, ESPECIALLY ACROSS THE SOUTHERN HALF OF  
THE CWA. RAIN WILL CHANGE TO SNOW OVER THE HILLS, RESULTING IN AN  
INCH OR TWO OF SNOWFALL BY SATURDAY MORNING. AS THE LOW SHIFTS  
EASTWARD, PRECIPITATION WILL END SATURDAY. SKIES WILL REMAIN MOSTLY  
CLOUDY DURING THE DAY, AND HIGHS WILL BE IN THE 50S.  
 
BRIEF UPPER RIDGING WILL ALLOW FOR A MILD AND DRY DAY SUNDAY, WITH  
HIGHS IN THE 60S. HOWEVER, RAIN RETURNS MONDAY AS A SHORTWAVE PUSHES  
THROUGH THE REGION. THE CANADIAN IS NOW ALIGNING MORE WITH THE ECMWF  
AND GFS, HOLDING OFF RAIN UNTIL MONDAY AFTERNOON. THE ECMWF IS THE  
SLOWEST OF THE THREE, SHOWING PRECIP LINGERING INTO TUESDAY  
AFTERNOON. ISOLATED THUNDERSTORMS WILL BE POSSIBLE MONDAY AFTERNOON  
AND EVENING, AND THEN RAIN WILL CHANGE TO SNOW ACROSS NORTHEASTERN  
WY AND THE BLACK HILLS MONDAY NIGHT. ONE OR TWO INCHES OF SNOW WILL  
BE POSSIBLE IN THOSE PLACES. A HALF TO THREE-QUARTERS OF AN INCH OF  
RAIN WILL BE POSSIBLE ACROSS PARTS OF THE AREA; MODELS ARE CURRENTLY  
INDICATING NORTHWESTERN SD AND FAR NORTHEASTERN WY WILL RECEIVE THE  
MOST.  
 
UPPER RIDGING SHOULD KEEP WEATHER DRY AND MILD MUCH OF NEXT WEEK.  
THE ECMWF AND GFS ARE HINTING AT A FAST-MOVING CANADIAN SHORTWAVE  
DIVING INTO THE NORTHERN PLAINS WEDNESDAY NIGHT, BUT THE FORECAST  
REMAINS DRY AT THIS TIME.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)  
ISSUED AT 1040 PM MDT FRI APR 20 2018  
 
IFR/LIFR CIGS WILL CONTINUE OVER THE BLACK HILLS AND NEAR THE  
EASTERN/SOUTHERN FOOTHILLS OVERNIGHT, INCLUDING AT KRAP. HIGHER  
ELEVATIONS WILL ALSO EXPERIENCE IFR/LIFR VSBYS IN FG. SURROUNDING  
THIS AREA, MVFR CIGS ARE EXPECTED OVER SOUTHWESTERN SD AND  
PORTIONS OF NORTHEASTERN WY. MVFR CIGS COULD TEMPORARILY IMPACT  
KGCC THROUGH ABOUT 10Z, BUT VFR CONDITIONS SHOULD PREVAIL.  
 
MVFR CIGS MAY LINGER OVER PORTIONS OF SOUTHWESTERN/SOUTH CENTRAL  
SD THROUGH EARLY SATURDAY AFTERNOON. OTHERWISE, VFR CONDITIONS ARE  
EXPECTED ACROSS THE AREA AFTER DAYBREAK.  
 

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

 
 

 
 
DISCUSSION...POJORLIE  
AVIATION...SHERBURN  
 
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