807  
FXUS63 KUNR 310443  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
1043 PM MDT SAT MAY 30 2020  
   
DISCUSSION
 
(THIS EVENING THROUGH SATURDAY)  
ISSUED AT 157 PM MDT SAT MAY 30 2020  
 
19Z SURFACE ANALYSIS HAD HIGH FROM EASTERN ND INTO MO. LEE  
TROUGH/WARM FRONT FROM CENTRAL MT INTO NORTHEAST CO. FAIRLY TIGHT  
GRADIENT BRINGING GUSTY SOUTHEASTERLY WINDS AT TIMES, UPSLOPE  
FLOW, AND SLOW INCREASE IN MOISTURE. THERMAL RIDGE OVER TOPPING  
CLOUD COOLED AIR PRODUCING 100-150J/KG MLCIN OVER NORTHEAST WY  
WITH ABOUT 500J/KG MLCAPE. 0.5KM VISIBLE LOOP SHOWED STABLE  
STRATUS/STRATOCU OVER WESTERN SD AND CLEAR SKIES OVER NORTHEAST  
WY. BIG HORNS CU HAVING TROUBLE DEVELOPING. SHORTWAVE IS SUGGESTED  
BY WATER VAPOUR OVER WESTERN WY, WHICH WILL HEAD NORTHEAST  
TONIGHT. IT'S GOING TO BE TOUGH TO INITIATE CONVECTION OVER  
NORTHEAST WY, BUT IT'S CONCEIVABLE STORMS THAT FIRE OVER THE  
TERRAIN FROM NORTH CENTRAL TO CENTRAL WY MIGRATES INTO CAMPBELL  
COUNTY THIS EVENING WITH ENOUGH SHEAR TO BE WATCHABLE. BRIEF  
TCU/TS OVER THE HIGHEST TERRAIN OF THE BLACK HILLS ALSO POSSIBLE  
EARLY. CONTINUED SOUTHEAST BOUNDARY LAYER FLOW WILL CREATE STRATUS-  
FEST OVER THE SD PLAINS TONIGHT. TEMPERATURES WILL BE NEAR GUIDANCE.  
 
SUNDAY, UPPER/THERMAL RIDGE BUILDS INTO THE CWA. STRATUS ON THE  
WESTERN SD PLAINS WILL ERODE IN THE AFTERNOON AS SOLAR INSOLATION  
TAKES HOLD ALONG EASTWARD MOVING WARM FRONT. IF THE WARM FRONT  
DOESN'T HEAD EAST, COULD BE A HUGE BUST IN HIGH TEMPERATURES EAST OF  
THE BLACK HILLS. 2KJ/KG SBCAPE FORECAST FROM THE NORTHERN BLACK  
HILLS INTO NORTHWEST SD LATER SUNDAY AFTERNOON, BUT 50-100J/KG  
SBCIN. INITIATING SURFACE-BASED CONVECTION WILL AGAIN BE TOUGH,  
BUT DO EXPECT TSRA TO DEVELOP IN MT, WHICH WILL TRANSLATE EASTWARD  
LATE AFTERNOON. IF WELL-DEFINED COLD POOL CAN DEVELOP, IT MIGHT  
BE ENOUGH FOR UPSCALE GROWTH LATE IN THE DAY OVER NORTHWEST SD WITH  
SEVERE WIND THREAT. CAMS INSISTENT ON THIS SCENARIO, BUT PARAMETERS  
NOT SO MUCH. TEMPERATURES WILL BE NEAR GUIDANCE IF CLOUDS GO AWAY.  
 
MONDAY THROUGH TUESDAY AFTERNOON, UPPER RIDGE SLIDES EAST AS THERMAL  
RIDGE PEAKS OVER THE CWA MONDAY - THE WARMEST DAY OF THE UPCOMING  
WEEK MOST LIKELY. CAN'T RULE OUT A STRAY STORM, BUT MOST AREAS WILL  
BE DRY.  
 
TUESDAY NIGHT THROUGH THE END OF NEXT WEEK, ACTIVE WEST/SOUTHWEST  
FLOW EXPECTED AS A SERIES OF WAVES PUSH FRONTAL BOUNDARIES ACROSS  
THE CWA. ACTIVE SEVERE WEATHER POSSIBLE GIVEN PATTERN. TEMPERATURES  
WILL BE 10-15F ABOVE NORMAL.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)  
ISSUED AT 1038 PM MDT SAT MAY 30 2020  
 
OVER WESTERN SD, AREAS OF MVFR/IFR CONDITIONS EXPECTED DUE TO  
STRATUS OVERNIGHT, ESPECIALLY IN/NEAR THE BLACK HILLS WHERE SOME  
LIFR CONDITIONS/FOG WILL OCCUR. OVER NORTHEASTERN WY PLAINS,  
MAINLY VFR CONDITIONS EXPECTED WITH GUSTY SOUTHERLY WINDS. SOME  
MVFR CIGS ARE POSSIBLE EXTENDING OUT FROM THE HILLS. CONDITIONS  
WILL IMPROVE FROM WEST TO EAST SUNDAY MORNING, AS A WARM FRONT  
MOVES THROUGH THE AREA.  
 

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

 
 

 
 
DISCUSSION...HELGESON  
AVIATION...MLS  
 
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