971  
FXUS63 KUNR 240450  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
1050 PM MDT SAT JUN 23 2018  
   
DISCUSSION
 
(THIS EVENING THROUGH SATURDAY)  
ISSUED AT 314 PM MDT SAT JUN 23 2018  
 
UPPER AIR ANALYSIS SHOWS AN UPPER LOW ACROSS THE NORTHERN ROCKIES  
SWINGING SOUTHEASTWARD INTO WESTERN WYOMING. WEAK UPPER RIDGING OVER  
THE AREA IS QUICKLY GIVING WAY TO MORE ACTIVE SOUTHWEST FLOW ALOFT,  
WITH A STRONG WAVE PUSHING THROUGH WYOMING. A SECOND WEAKER UPPER  
LOW IS ACROSS CENTRAL TO EASTERN DAKOTAS. SURFACE LOW PRESSURE  
HAS SET UP ACROSS ALONG THE WESTERN DAKOTAS, WITH NORTHERLY LOW  
LEVEL FLOW ACROSS THE REGION. THUNDERSTORMS ASSOCIATED WITH THE  
DAKOTA UPPER LOW WILL CONTINUE AFFECTING NW/CENTRAL SD OVER THE  
NEXT FEW HOURS BEFORE MOVING EAST OF THE CWA. AS UPPER FLOW  
BECOMES MORE SOUTHWESTERLY AND UPPER WAVE APPROACHES FROM THE  
WEST, STORMS WILL INCREASE IN COVERAGE LATE THIS AFTERNOON INTO  
TONIGHT...ESPECIALLY ACROSS NORTHEAST WYOMING, THE BLACK HILLS  
AREA, AND SOUTHWEST SD. MODELS ARE SHOWING MLCAPE OF 1000-1500  
J/KG, BUT SHEAR WILL BE QUITE WEAK. THE EXCEPTION MAY BE INCREASE  
EFFECTIVE BULK SHEAR ACROSS NORTHEAST WY/SW SD IN THE EVENING  
HOURS AHEAD OF THE APPROACHING UPPER WAVE. WILL CONTINUE TO SEE  
STRONG THUNDERSTORMS DEVELOP WITH PERHAPS ISOLATED SEVERE STORMS  
AS WELL. WITH SATURATED SOILS, FLOODING THREAT WILL CONTINUE WITH  
THIS SYSTEM ALL THE WAY THROUGH MONDAY AS THE UPPER LOW CROSSES  
THE REGION. SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH SUNDAY  
INTO SUNDAY EVENING. THE BULK OF THE RAINFALL WILL OCCUR DURING  
THIS PERIOD WITH MANY AREAS SEEING ANOTHER INCH OR TWO. LATEST  
MODELS HAVE SHIFTED QPF NORTHWARD INTO NORTHERN CAMPBELL COUNTY IN  
WY AND THE LAWRENCE/MEADE FOOTHILLS IN WESTERN SD, SO HAVE ADDED  
THESE ZONES TO THE FLOOD WATCH. THE UPPER LOW STALLS ACROSS  
SOUTHEASTERN SD MONDAY WITH WRAP AROUND PRECIP CONTINUING, BUT  
WITH DRIER AIR MIXING IN, POPS WON'T BE AS HIGH AS TONIGHT OR  
TOMORROW. UPPER RIDGING WILL BRING MUCH DRIER WEATHER TO THE AREA  
TUESDAY AND WEDNESDAY...BUT MODELS ARE SHOWING A SHORTWAVE  
CROSSING NW SD TUE NIGHT WHICH MIGHT BRING SOME SHOWERS AND  
STORMS. TOWARD THE SECOND HALF OF NEXT WEEK, IT'S LOOKING WET AND  
ACTIVE AGAIN AS ANOTHER UPPER LOW STALLS OUT OVER THE WESTERN  
CONUS.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)  
ISSUED AT 1050 PM MDT SAT JUN 23 2018  
 
COVERAGE OF SHRA AND POSSIBLY SOME TSRA WILL INCREASE OVERNIGHT  
ACROSS MOST OF NORTHEAST WY INTO THE BLACK HILLS AND SOUTHWESTERN  
SD. MVFR TO LOCALIZED IFR CONDITIONS ARE EXPECTED IN THESE  
SHRA/TSRA ACROSS NORTHEAST WY AND THE BLACK HILLS. MVFR CONDITIONS  
WILL GRADUALLY IMPROVE TO VFR ACROSS MOST OF THE AREA TOMORROW  
AFTERNOON, ALTHOUGH SHRA MAY CONTINUE ACROSS PORTIONS OF WESTERN  
SD FOR MUCH OF THE DAY.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 314 PM MDT SAT JUN 23 2018  
 
A LONG DURATION OF SHOWERS/STORMS IS EXPECTED TONIGHT INTO  
MONDAY. PWATS 125-150% OF NORMAL, SLOW STORM MOTION, AND ALREADY  
SATURATED SOILS SUGGEST THE POTENTIAL FOR FLOODING. MODELS  
ARE NOW SHOWING HIGHER QPF AMOUNTS OF 1-2 INCHES ACROSS NORTHEAST  
WYOMING INTO THE BLACK HILLS AREA, AND AREAS SOUTH AND EAST OF THE  
BLACK HILLS TO SOUTH CENTRAL SOUTH DAKOTA. HAVE ADDED NORTHERN  
CAMPBELL COUNTY IN WYOMING AND THE LAWRENCE/MEADE COUNTY FOOTHILLS  
IN WESTERN SOUTH DAKOTA TO THE FLOOD WATCH.  
 

 
   
UNR WATCHES/WARNINGS/ADVISORIES
 
 
SD...FLOOD WATCH THROUGH MONDAY AFTERNOON FOR SDZ024>032-041>044-046-  
047-049-072-074.  
 
WY...FLOOD WATCH THROUGH LATE SUNDAY NIGHT FOR WYZ054>058.  
 

 
 

 
 
DISCUSSION...13  
AVIATION...SHERBURN  
HYDROLOGY...13  
 
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