601  
FXUS65 KCYS 200604  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1104 PM MST FRI DEC 19 2014  
   
UPDATE
 
 
ISSUED AT 852 PM MST FRI DEC 19 2014  
 
NO CHANGES TO THE FORECAST THIS EVENING AND NO BIG WEATHER  
CONCERNS THROUGH TONIGHT. GUSTY WINDS WILL BE FOUND ALONG THE  
LARAMIE RANGE AND NORTHERN SNOWY RANGE FOOTHILLS. GUSTS OF 40 TO  
50 MPH WILL BE COMMON BUT NOT EXPECTING HIGH WIND CRITERIA. THE  
STRONG WINDS WILL HOLD OFF UNTIL TOMORROW NIGHT AND CONTINUE INTO  
SUNDAY NIGHT.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH SUNDAY)  
ISSUED AT 300 PM MST FRI DEC 19 2014  
 
GENERALLY QUIET WEATHER EXPECTED TONIGHT AND SATURDAY WITH JUST  
SOME SNOW SHOWERS OCCURRING OVER THE HIGHER MTNS AT TIMES AS WEAK  
RIPPLES IN GENERALLY WNWLY FLOW PASS BY WITH ACCOMPANYING ENHANCED  
MOISTURE RIDING UP WEST-FACING SLOPES. CHANGES ENSUE ON SUNDAY AS  
JET ENERGY RIDES OFF THE PACIFIC NW AND TURNS SE OVER THE REGION  
WHILE SFC PRESSURE FALLS OCCUR OVER THE HIGH PLAINS...SETTING UP A  
FAVORABLE WIND PATTERN IN WIND-PRONE AREAS. AT THE SAME TIME  
INCREASING MOISTURE WILL RIDE UP THE MOUNTAINS LATE SUNDAY  
INCREASING SNOWFALL. AS A RESULT CURRENT HILITES LOOK TO BE IN  
GOOD SHAPE AND WILL NOT ALTER AT THIS TIME. MILD TEMPS OVER THE  
PLAINS SUNDAY WITH DOWNSLOPING FLOW WITH MAXS APPROACHING 50F IN A  
FEW AREAS.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH FRIDAY)  
ISSUED AT 300 PM MST FRI DEC 19 2014  
 
SUNDAY NIGHT...POTENT SHORTWAVE TROUGH...ALBERTA CLIPPER  
SYSTEM...MOVES SOUTHEAST ACROSS THE DAKOTAS...SENDING A COLD FRONT  
ACROSS OUR COUNTIES AND CRANKING UP OUR WINDS. DEEP MOISTURE IN  
NORTHWEST FLOW ALOFT WILL KEEP THE OROGRAPHIC SNOW MACHINE CRANKING  
ACROSS THE SNOWY AND SIERRA MADRE RANGES WITH A CHANCE OF SNOW  
ELSEWHERE IN CYCLONIC FLOW ALOFT.  
 
MONDAY...IF YOU LOVE WINDY...COLD WEATHER...YOU WILL ENJOY THIS DAY  
AS BRISK NORTHWEST FLOW FROM THE SURFACE TO 500 MB PREVAILS. BASED  
ON THE 700 MB GRADIENTS AND DEEP COLD AIR ADVECTION...WE MAY NEED  
HIGH WIND WARNINGS ACROSS MUCH OF SOUTHEAST WYOMING...ESPECIALLY  
OVER OUR WIND PRONE LOCALES SUCH AS ARLINGTON...VEDAUWOO AND THE  
SUMMIT OF INTERSTATE 80...ALONG WITH WIND ADVISORIES OVER WESTERN  
NEBRASKA. OROGRAPHIC SNOWS WILL DECREASE IN COVERAGE OVER THE SNOWY  
AND SIERRA MADRE RANGES AS MOISTURE WANES SLIGHTLY.  
 
TUESDAY...WILL BE A GOOD TRAVEL DAY FOR THE PRE CHRISTMAS TRAVEL  
PERIOD. PRIMARY ISSUE WILL BE WINDS AS THE 700 MB GRADIENTS SUGGEST  
A TYPICALLY WINDY DAY...WITH PERHAPS OUR WIND PRONE LOCALES SUCH AS  
ARLINGTON...VEDAUWOO...BORDEAUX AND THE INTERSTATE 80 SUMMIT  
APPROACHING HIGH WIND CRITERIA. ONLY SNOW EXPECTED WILL BE OVER THE  
SNOWY AND SIERRA MADRE RANGES...AND ONLY SCATTERED SNOW  
SHOWERS...DRY ELSEWHERE.  
 
CHRISTMAS EVE DAY...ANOTHER GOOD TRAVEL DAY FOR THE PRE CHRISTMAS  
TRAVEL AS THE FLOW ALOFT BACKS TO NORTHWEST WITH A TRANSITORY FAST  
MOVING SHORTWAVE RIDGE OVERHEAD. ASIDE FROM A FEW MOUNTAIN SNOW  
SHOWERS OVER THE SNOWY...SIERRA MADRE AND NORTHERN LARAMIE  
RANGES...NO PRECIPITATION EXPECTED. WILL BE A WARMER AND WINDY DAY  
BASED ON PROJECTED GRADIENTS...BUT MINIMAL TRAVEL ISSUES.  
 
CHRISTMAS...IF YOU LOVE SEEING SNOW ON CHRISTMAS DAY...YOU MAY BE  
PLEASED. WHILE THE TYPICALLY DRIER GFS KEEPS CHRISTMAS EVE MORNING  
DRY WITH THE APPROACHING SHORTWAVE TROUGH OVER IDAHO...THE  
ECMWF...TYPICALLY PERFORMING BETTER IN THE WINTER...SHOWS A MORE  
WELL PRONOUNCED SHORTWAVE TROUGH ALOFT APPROACHING FROM IDAHO WITH  
SNOW SPREADING INTO OUR WESTERN COUNTIES WEST OF A DOUGLAS TO  
LARAMIE LINE BY CHRISTMAS DAY DAWN...AND WILL GO WITH THIS SOLUTION  
WHICH BLENDS WELL WITH OUR SURROUNDING OFFICES.  
 
FOR THE DAYLIGHT HOURS ON CHRISTMAS...THE ECMWF CONTINUES TO MOVE  
THE WELL PRONOUNCED SHORTWAVE TROUGH ALOFT OVER WYOMING WITH A  
DECENT ARCTIC INTRUSION COLD FRONT AND WIDESPREAD SNOW BY LATE  
AFTERNOON WEST OF A CHEYENNE TO CHADRON LINE...WHEREAS THE GFS IS  
LESS BULLISH WITH QPF AND SNOWFALL AND BRINGS THE COLD FRONT IN  
LATER IN THE DAY. SINCE THE ECMWF TYPICALLY OUTPERFORMS THE MORE  
OFTEN DRIER GFS IN THE WINTER...AND SINCE THE ECMWF SOLUTION IS  
CLOSE TO THE ONE FROM YESTERDAY...ALBEIT A TAD SLOWER...WILL SIDE  
WITH OUR SURROUNDING OFFICES AND PAINT AT LEAST A CHANCE OF  
AFTERNOON SNOW ACROSS MOST OF OUR COUNTIES...WITH WIDESPREAD  
OROGRAPHIC SNOWS ACROSS OUR NORTHERN LARAMIE...SNOWY AND SIERRA  
MADRE RANGES.  
 
FRIDAY...LOOKS LIKE ANOTHER DECENT TRAVEL DAY AS BOTH THE GFS AND  
ECMWF SHOW THE SHORTWAVE TROUGH ALOFT MOVING TO THE EAST OF OUR  
FORECAST AREA...WITH DECREASING CHANCES FOR SNOW...AND WINDY AND  
COLD CONDITIONS PER PROGGED GRADIENTS AND THICKNESSES.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)  
ISSUED AT 1102 PM MST FRI DEC 19 2014  
 
VFR OVER A VAST MAJORITY OF THE FORECAST AREA THROUGH THE TAF  
PERIOD...BUT MOUNTAIN TOPS WILL BE OBSCURED OVER SOUTH CENTRAL  
WYOMING. A FEW SNOW SHOWERS POSSIBLE INTO THE SNOWY AND SIERRA  
MADRE RANGES LATE TONIGHT INTO SATURDAY BUT SNOW WILL BECOME  
PERSISTENT WITH MOUNTAINS OBSCURRED SATURDAY NIGHT THROUGH SUNDAY  
NIGHT WITH PERIODS OF HEAVY SNOW A GOOD POSSIBILITY. STRONG WINDS  
TO DEVELOP OVER SOUTHEAST WYOMING LATE SATURDAY NIGHT THROUGH  
SUNDAY...ESPECIALLY IN THE TYPICALLY WIND PRONE AREAS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 300 PM MST FRI DEC 19 2014  
 
INCREASING WINDS AROUND THE MOUNTAINS WILL BE THE MAIN CONCERN  
OVER THE WEEKEND BUT OTHER FACTORS EXPECTED TO BE NON-CRITICAL.  
SNOW SHOWERS WILL INCREASE OVER THE MTNS BEGINNING SUNDAY AND  
PERSIST INTO EARLY NEXT WEEK. ELSEWHERE MAINLY DRY AND COOL  
WEATHER WILL CONTINUE.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY  
AFTERNOON FOR WYZ112-114.  
 
HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY EVENING  
FOR WYZ106-110.  
 
HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR  
WYZ116-117.  
 
NE...NONE.  
 

 
 

 
 
UPDATE...SML  
SHORT TERM...RE  
LONG TERM...RUBIN  
AVIATION...SML  
FIRE WEATHER...RE  
 
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