105  
FXUS63 KUNR 201116  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
516 AM MDT SUN AUG 20 2017  
   
DISCUSSION
 
(TODAY THROUGH SATURDAY)  
ISSUED AT 203 AM MDT SUN AUG 20 2017  
 
A WEAK UPPER WAVE PUSHING THROUGH MT IS CREATING SOME  
SHOWERS AND THUNDERSTORMS ACROSS NORTHWESTERN SD AND FAR  
NORTHEASTERN WY. AT THE SURFACE, HIGH PRESSURE IS MOVING INTO THE  
NORTHERN PLAINS BEHIND THE COLD FRONT, AND A LOW SITS OVER CENTRAL  
SD. WINDS ACROSS THE NORTHWESTERN 2/3 OF THE CWA ARE NORTHERLY  
AROUND 10 KTS, WITH SOUTHERLY WINDS ACROSS SOUTH CENTRAL SD.  
TEMPERATURES ARE FALLING INTO THE 60S.  
 
SHOWERS AND THUNDERSTORMS WILL GRADUALLY DISSIPATE AND MOVE OUT OF  
THE CWA THIS MORNING. AS THE SURFACE HIGH SLIDES THROUGH ND,  
EAST/SOUTHEAST WINDS WILL BECOME A LITTLE BREEZY. MODELS CONTINUE TO  
SHOW LESS CAPE ACROSS THE CWA, AS WELL AS PLENTY OF CIN, ALTHOUGH  
THERE COULD BE A FEW STORMS THAT CLIP SOUTH CENTRAL SD THIS  
EVENING. LOW-LEVEL JET AHEAD OF AN APPROACHING TROUGH WILL RESULT  
IN INCREASED INSTABILITY ACROSS NORTHEASTERN WY AND PORTIONS OF  
WESTERN SD OVERNIGHT, AND THE CAP MAY WEAKEN ENOUGH ACROSS  
NORTHWESTERN SD FOR A FEW THUNDERSTORMS TO DEVELOP; HOWEVER, CAMS  
ARE NOT IN AGREEMENT ABOUT THAT. SHEAR AROUND 50 KTS COULD SUPPORT  
AN ISOLATED SEVERE STORM. HIGHS TODAY WILL BE IN THE 80S, WITH  
LOWS TONIGHT IN THE UPPER 50S.  
 
OVERNIGHT SHOWERS AND THUNDERSTORMS MAY CONTINUE INTO MONDAY MORNING  
ACROSS PARTS OF WESTERN SD. THE GFS AND ECMWF ARE MORE EXCITED ABOUT  
MORNING PRECIPITATION THAN THE CANADIAN, NAM, AND MANY OF THE CAMS.  
IT'S STILL LOOKING LIKE THERE WILL BE CLOUDS AROUND DURING THE  
ECLIPSE, MORE SO ACROSS WESTERN SD THAN NORTHEASTERN WY. HOWEVER,  
MODELS ARE HINTING AT SOME CLEARING MORE THAN THEY WERE YESTERDAY.  
 
UPPER RIDGE WILL BRING WARM AND DRY WEATHER FOR TUESDAY AND  
WEDNESDAY, WITH HIGHS IN THE 80S. CHANCES FOR PRECIPITATION WILL  
RETURN TOWARDS THE END OF THE WEEK, AS A TROUGH BEGINS TO BREAK DOWN  
THE RIDGE AND PLACES THE AREA IN MORE ACTIVE SOUTHWEST FLOW.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 514 AM MDT SUN AUG 20 2017  
 
ISOLATED SHOWERS AND THUNDERSTORMS WILL END EARLY THIS MORNING  
ACROSS NORTHWEST SOUTH DAKOTA. ADDITIONAL THUNDERSTORMS WILL  
DEVELOP LATE THIS AFTERNOON, WITH COVERAGE INCREASING ACROSS  
WESTERN SOUTH DAKOTA THIS EVENING/OVERNIGHT. MVFR/LOCAL IFR  
CONDITIONS WITH THE THUNDERSTORMS, ESPECIALLY TONIGHT. OTHERWISE,  
VFR CONDITIONS EXPECTED.  
 

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

 
 

 
 
DISCUSSION...POJORLIE  
AVIATION...7  
 
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