Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 182207
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
308 PM MST THU DEC 18 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 300 PM MST THU DEC 18 2014

FAIRLY QUIET WEATHER EXPECTED OVERALL THE NEXT COUPLE DAYS WITH
JUST SOME SNOW SHOWERS OVER THE HIGHER MTNS AT TIMES AS A COUPLE
WEAK SHORTWAVES PASS BY. ONE WILL SCOOT ACROSS EARLY FRIDAY WHILE
ANOTHER SWINGS ACROSS LATER SATURDAY. THESE WILL ENHANCE SNOW
SHOWERS OVER THE HIGHER MTNS AS WELL AS WINDS AROUND THE MTNS.
TEMPS WILL REMAIN ON THE COOL SIDE...BUT CLOSE TO SEASONAL
AVERAGES. ONE DIFFICULTY WILL STILL BE EFFECTS FROM GOOD SNOW
COVER OVER THE PANHANDLE...WHERE COLD AIR TRAPPING IN THE NORTH
PLATTE RIVER VALLEY KEPT TEMPS IN THE 20S TODAY. COULD BE SOME
FOG THERE AGAIN TONIGHT THOUGH A LIGHT DOWNSLOPE BREEZE WILL
HOPEFULLY LIMIT ITS THICKNESS SOME. WENT ON THE COOL SIDE FOR MAXS
THERE ON SATURDAY.

.LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 300 PM MST THU DEC 18 2014

SUNDAY...WINDY DAY PER PROGGED SURFACE THROUGH 700 MB GRADIENTS AND
DEEP UNIDIRECTIONAL NORTHWEST FLOW ALOFT. LONG DURATION HEAVY
SNOWFALL EVENT WILL CRANK UP OVER OUR SNOWY AND SIERRA MADRE
RANGES...AND TO A LESSER EXTENT OVER THE NORTHERN LARAMIE RANGE
BASED ON DECENT LOW AND MID LEVEL MOISTURE TRANSPORT WITH
OROGRAPHICS. WE WILL LIKELY BE ISSUING WINTER STORM WARNINGS FOR
LONG DURATION SNOWFALL EVENT OVER OUR SNOWY AND SIERRA MADRES...AND
POSSIBLY OVER THE NORTHERN LARAMIE RANGE.

MONDAY...COLD FRONT MOVES THROUGH IN STRONG NORTHWEST FLOW
ALOFT...WITH WINDY CONDITIONS PER PROGGED SURFACE THROUGH 700 MB
GRADIENTS...AND THE LONG DURATION OROGRAPHIC SNOWS WILL CONTINUE
ACROSS OUR NORTHERN LARAMIE...SNOWY AND SIERRA MADRE RANGES.
ISOLATED TO SCATTERED SNOW SHOWERS ELSEWHERE IN COLD AIR ADVECTION
ALOFT.

TUESDAY...FLOW ALOFT TURNS MORE NORTHERLY WITH OROGRAPHIC SNOWS
DECREASING TO ONLY OVER THE MOUNTAINS...AND DRY ELSEWHERE DUE TO
LIMITED LOW AND MID LEVEL MOISTURE. DECENT TRAVEL PERIOD FOR
CHRISTMAS TRAVEL WITH RESPECT TO SNOWFALL ONLY OVER THE
MOUNTAINS...ALBEIT WITH TYPICALLY BRISK WINDS PRODUCING OUR TYPICAL
WINDY SEASON WINDS.

CHRISTMAS EVE DAY (WEDNESDAY)...CHANCES FOR A WHITE CHRISTMAS
EVE...AND CHRISTMAS...ARE LOOKING INCREASINGLY LIKELY...ESPECIALLY
WITH A PREFERENCE FOR THE ECMWF SOLUTION SHOWING NEXT DECENT
SHORTWAVE TROUGH ALOFT CARVING OUT OVER IDAHO WITH THE ASSOCIATED
BAND OF SNOWFALL EXTENDING ACROSS THE SOUTHERN HALF OF WYOMING BY
THE EVENING OF CHRISTMAS EVE. QPF SOLUTION ON THE GFS LOOKS TOO FAR
NORTH...AND ESPECIALLY WITH THE TYPICAL GFS DRY BIAS IN THE WINTER.

CHRISTMAS DAY...IF YOU LOVE SNOW ON CHRISTMAS DAY...YOU WILL LOVE
THE FACT THAT THE GFS AND ECMWF ARE STRIKINGLY SIMILAR IN DEPICTING
A WELL PRONOUNCED SHORTWAVE TROUGH ALOFT OVER SOUTHWEST WYOMING WITH
BOTH MODELS SHOWING A DECENT BAND OF LIGHT TO MODERATE SNOW
EXTENDING ACROSS SOUTHERN WYOMING AND NORTHERN COLORADO...WITH THE
ECMWF SLIGHTLY FURTHER NORTH WITH THE SNOW BAND OVER OUR
COUNTIES...THUS FEEL CONFIDENT ENOUGH WITH EXPERIENCE AND BOTH
MODELS CONGRUITY...TO BOOST OUR SNOWFALL POPS INTO THE 30 TO 70
PERCENT RANGE SOUTH OF A DOUGLAS TO KIMBALL LINE. IF ALL COMES
TOGETHER AS THE MODELS INDICATE...WE WILL SEE ACCUMULATING SNOW DUE
TO THE BAROCLINIC BAND...UPSLOPE AND CYCLONIC CURVATURE LIFTING
FEATURES...WITH SNOWFALL DECREASING IN AREAL COVERAGE CHRISTMAS
AFTERNOON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY MORNING)
ISSUED AT 1045 AM MST THU DEC 18 2014

VFR EXPECTED OVERALL THROUGH THE PERIOD WITH LIGHT WINDS. SOME
FOG MAY REDEVELOP IN THE NORTH PLATTE RIVER VALLEY TONIGHT BUT A
MORE DOWNSLOPE BREEZE SHOULD LIMIT ITS EXTENT OR DENSITY.

&&

.FIRE WEATHER...
ISSUED AT 300 PM MST THU DEC 18 2014

NO CONCERNS SEEN THROUGH THE WEEKEND WITH MOSTLY NON-CRITICAL
CONDITIONS. WINDS WILL INCREASE OVER THE WEEKEND BUT OTHERWISE
COOL TEMPERATURES WILL PREVAIL WITH MTN SNOW SHOWERS AT TIMES.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

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


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