717  
FXUS63 KUNR 261709  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
1109 AM MDT MON JUN 26 2017  
   
DISCUSSION
 
(TODAY THROUGH SUNDAY)  
ISSUED AT 142 AM MDT MON JUN 26 2017  
 
UPPER ANALYSIS SHOWS A LARGE RIDGE OVER THE WESTERN CONUS, WITH A  
90 KT JET OVER THE NORTHERN PLAINS IN NORTHWEST FLOW. SKIES ARE  
CLEAR ACROSS THE CWA. WITH A SURFACE HIGH OVER THE DAKOTAS, WINDS  
ARE LIGHT AND VARIABLE. TEMPERATURES AT 2 AM ARE IN THE MID 40S  
TO MID 50S.  
 
ANOTHER WARM AND DRY DAY IS EXPECTED, AS THE UPPER RIDGE SHIFTS OVER  
THE ROCKIES. HIGHS WILL BE IN THE MID 70S TO THE MID 80S, AND  
MINIMUM RELATIVE HUMIDITY VALUES WILL BE 15-20% ACROSS NORTHEASTERN  
WY. SOUTHERLY WINDS WILL BE AROUND 10 TO 15 MPH. WINDS WILL BECOME  
BREEZIER OVERNIGHT AS THE PRESSURE GRADIENT TIGHTENS, KEEPING LOWS  
IN THE 50S TO LOWER 60S.  
 
TUESDAY WILL BE HOT, WITH HIGHS AROUND 90, AS THE THERMAL RIDGE  
SHIFTS OVER THE AREA. GUSTY SOUTHERLY WINDS WILL CONTINUE,  
ESPECIALLY ACROSS SOUTH CENTRAL SD. THESE STRONG WINDS WILL ADVECT  
IN WARM, MOIST AIR, RESULTING IN DEW POINTS IN THE 50S. MODELS VARY  
ON THEIR ML CAPE FORECASTS FOR TUESDAY AFTERNOON, BUT ABOUT 1500 TO  
2000 J/KG IS EXPECTED ACROSS WESTERN SD BY 18Z. THE UPPER RIDGE WILL  
BREAK DOWN TUESDAY AS A WAVE PUSHES INTO THE REGION, AND CONVECTION  
WILL INITIATE ACROSS WESTERN SD DURING THE AFTERNOON. WITH 0-6 KM  
SHEAR AROUND 40 KTS, SUPERCELLS WILL BE POSSIBLE. THE TROUGH WILL  
QUICKLY PUSH INTO THE EASTERN DAKOTAS, AND MOST OF THE ACTIVITY WILL  
ALSO SHIFT EAST INTO CENTRAL SD BY EARLY EVENING. HOWEVER, SOME  
ADDITIONAL STORMS WILL POSSIBLE ACROSS WESTERN SD WITH THE COLD  
FRONT LATER TUESDAY EVENING.  
 
THE ACTIVE PATTERN WILL KEEP CHANCES FOR THUNDERSTORMS IN THE  
FORECAST THROUGH THE END OF THE WEEK, BUT INSTABILITY IS WEAK TO  
MARGINAL COMPARED TO TUESDAY. THE NEXT MAIN WAVE IS PROGGED TO MOVE  
THROUGH THURSDAY. HIGHS WILL BE IN THE 70S AND 80S, AND LOWS WILL BE  
IN THE 50S.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY)  
ISSUED AT 1104 AM MDT MON JUN 26 2017  
 
VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT. A LOW LEVEL JET  
DEVELOPING THIS EVENING AHEAD OF AN APPROACHING COLD FRONT MAY  
BRING SOME LOW LEVEL WIND SHEAR TO NORTHEAST WY AND WESTERN SD  
LATE THIS EVENING AND THROUGH THE NIGHT.  
 

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

 
 

 
 
DISCUSSION...POJORLIE  
AVIATION...JOHNSON  
 
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