991  
FXUS63 KUNR 291725  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
1125 AM MDT THU JUL 29 2021  
   
DISCUSSION
 
(TODAY THROUGH WEDNESDAY)  
ISSUED AT 234 AM MDT THU JUL 29 2021  
 
08Z SURFACE ANALYSIS HAD HIGH PRESSURE OVER ND HAD PUSHED COLD  
FRONT INTO SOUTHERN WY/NE. WATER VAPOUR LOOP SHOWED UPPER RIDGE  
OVER THE CENTRAL PLAINS WITH NOTABLE WAVE/MONSOONAL MOISTURE OVER  
THE FOUR CORNERS REGION, WRAPPING INTO THE NORTHERN ROCKIES.  
EASTERLY 850-700MB FLOW FEEDING WEAK CONVECTION OVER NORTHEAST WY  
INTO NORTHWEST SD PER THETA-E ADVECTION/WEAK MUCAPE. MAIN CONCERN  
THIS FORECAST REVOLVES AROUND FOUR CORNERS WAVE.  
 
TODAY THROUGH FRIDAY, WAVE FLATTENS UPPER RIDGE AS IT MOVES INTO THE  
NORTHERN PLAINS TONIGHT INTO FRIDAY. SURFACE HIGH DRIFTS SOUTHEAST  
MAINTAINING EASTERLY COMPONENT/LOW LEVEL UPSLOPE FLOW. UPPER WAVE  
WILL SUPPORT LEE TROUGH AS IT MOVES EASTWARD TONIGHT. 500-750J/KG  
MLCAPE DEVELOPS THIS AFTERNOON/EVENING ACROSS THE FAR SOUTHWEST  
SIXTH OF THE CWA AS 0-6KM BULK SHEAR SETTLES AROUND 35KTS.  
ISOLATED STRONGER STORMS MAY DEVELOP FOR THOSE AREAS DURING PEAK  
HEATING. CLUSTER OF SHOWERS/STORMS AHEAD OF WAVE WILL MOVE ACROSS  
THE CWA TONIGHT INTO FRIDAY. CURRENT THINKING IS BEST CHANCE FOR  
BENEFICIAL RAINS WILL BE FROM NORTHEAST WY INTO SOUTHERN SD. GIVEN  
PWATS 150-200% OF NORMAL, LOCALLY HEAVY RAINS MAY OCCUR. MAIN  
BAND OF PRECIPITATION DIMINISHES FRIDAY NIGHT. TEMPERATURES WILL  
BE NOTICEABLY COOLER, ESPECIALLY FRIDAY.  
 
FOR THE WEEKEND INTO THE FIRST HALF OF NEXT WEEK, UPPER RIDGE WILL  
CONTINUE TO DOMINATE THE WEATHER. NORTHWEST FLOW ALOFT OVER THE  
WEEKEND TRANSITIONS TO WEST/SOUTHWEST FLOW MID-WEEK. TEMPERATURES  
WILL BE SEASONABLE AS WEAK DISTURBANCES BRING TRANSIENT CHANCES  
FOR STORMS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)  
ISSUED AT 1125 AM MDT THU JUL 29 2021  
 
ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE ACROSS MUCH OF  
THE AREA THROUGH LATE AFTERNOON, WITH SHOWERS AND STORMS BECOMING  
MORE WIDESPREAD FROM NORTHEAST WY TO WESTERN SD TONIGHT. MVFR  
CONDITIONS COULD DEVELOP WITH HEAVIER SHOWERS AND AREAS OF MVFR  
CEILINGS ARE LIKELY LATER TONIGHT INTO FRIDAY MORNING. INCREASING  
SMOKE FROM WILDFIRES IN SOUTH CENTRAL CANADA WILL ALSO LIKELY  
REDUCE VSBYS AT TIMES IN MANY AREAS, ESPECIALLY TONIGHT INTO  
FRIDAY.  
 

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

 
 

 
 
DISCUSSION...HELGESON  
AVIATION...26  
 
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