776  
FXUS63 KUNR 272019  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
219 PM MDT MON MAR 27 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY NIGHT)  
ISSUED AT 142 PM MDT MON MAR 27 2017  
 
LATEST ANALYSIS SHOWS AND UPPER RIDGE OVER THE CENTRAL CONUS AND  
THE CANADIAN PRAIRIE PROVINCES WITH AN UPPER TROUGH OVER THE  
WESTERN CONUS AND BRITISH COLUMBIA. IT IS THIS UPPER TROUGH THAT  
WILL AFFECT THE WEATHER OVER THE FORECAST AREA OVER THE NEXT FEW  
DAYS. THE UPPER TROUGH WILL APPROACH THE FORECAST AREA TONIGHT AND  
ON TUESDAY WITH AN UPPER LOW DEVELOPING OVER THE FOUR CORNERS  
REGION TONIGHT AND MOVING SLOWLY INTO NORTHERN TEXAS ON  
WEDNESDAY AS IT SPLITS FROM THE NORTHERN STREAM ENERGY ON TUESDAY.  
 
TONIGHT THROUGH TUESDAY NIGHT, MOIST WAA ALOFT WILL INCREASE OVER  
THE FORECAST AREA AS THE UPPER TROUGH APPROACHES FROM THE WEST.  
AT THE SURFACE, AN INVERTED TROUGH WILL DEVELOP OVER EASTERN  
WYOMING TONIGHT MOVING INTO WESTERN SOUTH DAKOTA EARLY ON TUESDAY.  
THE PRESSURE GRADIENT ASSOCIATED WITH THE SFC TROUGH WILL DEVELOP  
INTO SOUTHEASTERLY UPSLOPE FLOW OVER THE FORECAST AREA. 850-650MB  
FRONTOGENESIS WILL STRENGTHEN AS THE JET STREAK MOVES THROUGH  
ALOFT, INCREASING SYNOPTIC SCALE LIFT. LATEST MODELS ARE SHOWING  
THE MORE WIDESPREAD PRECIPITATION DEVELOPING AROUND 6 HOURS LATER  
THAN IN PREVIOUS RUNS, SO EXPECT TO SEE THE PRECIPITATION BEGIN TO  
INCREASE IN COVERAGE LATE THIS EVENING INTO THE EARLY MORNING  
HOURS. THE PRECIPITATION WILL BECOME MOST WIDESPREAD DURING THE  
DAY ON TUESDAY THEN WILL MOVE OFF TO THE SOUTHEAST LATE TUESDAY  
NIGHT/EARLY WEDNESDAY MORNING. BENEFICIAL RAINS ARE PROBABLE WITH  
LIQUID EQUIVALENTS 1"+ OVER AND NEAR THE BLACK HILLS, PARTS OF  
NORTHEASTERN WYOMING AND OVER FAR SOUTHWESTERN SOUTH DAKOTA.  
 
PRECIPITATION TYPE AND THE TIMING FOR A RAIN/SNOW CHANGEOVER OVER  
THE HIGHER ELEVATIONS OF THE BLACK HILLS AND POSSIBLY OVER THE FAR  
SOUTHWESTERN CORNER OF CAMPBELL COUNTY IN NORTHEASTERN WYOMING IS  
THE MAIN FORECAST CONCERN TONIGHT THROUGH TUESDAY NIGHT. WET BULB  
ZERO VALUES IN THE FORECAST SOUNDINGS ARE MARGINAL FOR SNOW, BUT  
EXPECTED SUSTAINED PRECIPITATION RATES ARE EXPECTED TO SUPPORT  
SEVERAL INCHES OF SNOW OVER THE HIGHER BLACK HILLS IN A COUPLE OF  
BATCHES, ONE LATER TONIGHT/EARLY TUESDAY AND THEN LATER  
TUESDAY/TUESDAY NIGHT. WITH THE RELATIVELY HIGH FORECAST WET BULB  
ZEROS, SNOW OVER THE HIGHER ELEVATIONS MAY CHANGE BACK TO RAIN  
DURING THE DIURNAL HEATING CYCLE ON TUESDAY. ALTHOUGH NOT  
CURRENTLY INDICATED, IF SLIGHTLY DRIER AIR DEVELOPS IN THE COLUMN,  
SUBSTANTIAL SNOW ACCUMULATIONS MAY OCCUR ABOVE 5500 FEET.  
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 142 PM MDT MON MAR 27 2017  
 
LINGERING PRECIPITATION WILL END ON WEDNESDAY AS THE PRECIPITATION  
MOVES OFF TO THE SOUTHEAST. DRY WEATHER WILL OCCUR ON THURSDAY.  
ANOTHER SPLITTING UPPER TROUGH WILL BRING MAINLY RAIN FROM  
THURSDAY NIGHT INTO EARLY SATURDAY. TEMPERATURES WILL BE 2-12F  
ABOVE AVERAGE THROUGH THE PERIOD.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY)  
ISSUED AT 142 PM MDT MON MAR 27 2017  
 
LOCALIZED IFR FOG WL LINGER EAST OF BLK HLS THRU EARLY AFTN. A  
STORM SYSTEM WILL BRING MOISTURE INTO THE AREA OVERNIGHT, WITH  
INCREASING CLDS AND PRECIPITATION. EASTERLY WNDS ALONG BLK HLS  
WILL BRING LOWER CLDS ARND MIDNIGHT, WHILE IFR CIGS WL DVLP OVR  
NERN WY AS SFC TROF PASSES. PRECIP WL BE RAIN IN MOST AREAS, BUT  
SNOW WL MIX IN NERN WY AND HIGHER ELEVATIONS.  
 

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

 
 

 
 
SHORT TERM...10  
LONG TERM...10  
AVIATION...10  
 
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