Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 221226
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
526 AM MST MON DEC 22 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 525 AM MST MON DEC 22 2014

SNOW AND HIGH WINDS CONTINUE TO BE OUR MAJOR CONCERNS OVER THE NEXT
24 TO 36 HOURS. LIGHT TO MODERATE SNOW SHOWERS HAVE BEEN ONGOING FOR
MUCH OF THE NIGHT ALONG AND EAST OF THE LARAMIE RANGE. ACCUMULATIONS
HAVE NOT BEEN SIGNIFICANT...BUT IT IS CAUSING A FEW TRAVEL HAZARDS
WITH SLICK ROADS AND LOCALLY REDUCED VISIBILITY. SNOW SHOWERS SHOULD
PERSIST TODAY IN THE FAVORED LEFT EXIT REGION OF A 160-180 KT JET AT
H25. NOT SO SURPRISINGLY...THIS PATTERN IS CONTRIBUTING TO QUITE THE
DUMPING OF SNOW IN THE MOUNTAINS. RECENT ANALYSIS OF AREA SNOTEL OBS
ESTIMATES OVER 30 INCHES OVER THE PAST 24 HOURS IN THE SNOWIES USING
A 15 TO 1 RATIO. EXPECT ANOTHER FOOT OR SO WILL FALL THROUGH EARLY
TUESDAY MORNING WITH MOST MODELS PAINTING SEVERAL TENTHS OF AN INCH
OF QPF IN A VERY FAVORABLE PATTERN FOR MOIST OROGRAPHICS AND EXTREME
DIVERGENCE ALOFT. WINTER STORM WARNING FOR THE MOUNTAINS IS IN GREAT
SHAPE...SO NO CHANGES NECESSARY THERE. WINDS SHOULD BECOME NORTHWEST
ACROSS ALL AREAS IN THE POST FRONTAL AIR MASS...SO ACCUMULATING SNOW
SHOULD END OVER SOUTHWEST CARBON COUNTY WITH THE LOSS OF FAVORABLE
LOW LEVEL UPSLOPE. LATEST HIGHWAY OBSERVATIONS INDICATE LESS THAN 30
MPH WINDS AT ARLINGTON AS WELL. AS SUCH...BELIEVE WE WILL BE ABLE TO
LET THOSE WINTER STORM WARNINGS EXPIRE AT 8 AM.

IT WILL BE WINDY YET AGAIN ACROSS MUCH OF THE AREA TODAY. COLD FRONT
SWEPT ACROSS THE AREA LAST EVENING AND WAS DRAPED ACROSS CENTRAL NE
INTO NORTHWESTERN KS AT 09Z. EXCELLENT COLD ADVECTION IS OCCURRING
ALOFT WITH H7 TEMPS PLUNGING SEVERAL DEG C OVER THE PAST FEW HOURS
PER LAPS SOUNDINGS. THIS IS KEEPING THINGS WELL-MIXED AND IS ALREADY
GIVING WAY TO GUSTS AROUND 40 MPH AT CHADRON. BOTH NAM/GFS FORECAST
SOUNDINGS SHOW AROUND 45 KT AVAILABLE TO MIX THROUGH THE DAY OVER
MOST OF THE PANHANDLE...SO WILL KEEP THE ADVISORY GOING. THINK
WINDS ALOFT ARE NOT QUITE HIGH ENOUGH TO JUSTIFY A WARNING...BUT
WE COULD SEE SOME GUSTS TO 55 MPH IN THE AFTERNOON. BIGGER WIND
CONCERNS ARE FOR THIS EVENING AND OVERNIGHT. THE MODELS STILL
CLOSE OFF THE UPPER LOW OVER THE CENTRAL PLAINS AFTER 00Z WITH
FAST NORTHWESTERLY FLOW ALOFT REMAINING IN PLACE OVER THE CWA. THE
GFS SHOWS A 995 MILLIBAR SURFACE LOW OVER IOWA AT 06Z
TONIGHT...RESULTING IN A STRONG SURFACE PRESSURE GRADIENT ALONG
AND EAST OF THE LARAMIE RANGE. GFS/NAM/ECMWF ALL BRING A BROAD
SWATH OF 55 TO 65 KT FLOW AT H7-H8 DURING THE LATE EVENING AND
OVERNIGHT HOURS. DOWNWARD MOMENTUM TRANSFER IS POSSIBLE AS MODELED
SOUNDINGS SUGGEST A VERY WELL-MIXED BOUNDARY LAYER OWING TO
CONTINUOUS CAA JUST OFF THE SURFACE. BUFKIT SOUNDINGS SUGGEST 30
TO 40 KT SUSTAINED AT THE LOWEST LEVEL AT CHEYENNE AND A FEW
OTHER SITES AROUND 06-08Z...WITH UPWARDS OF 65 KT AT THE TOP OF
THE MIXED LAYER. WILL HOIST A HIGH WIND WATCH STARTING AT 03Z FOR
ALL AREAS ALONG AND EAST OF THE LARAMIE RANGE. EXPECT WINDS WILL
SLOWLY RELAX BY TUESDAY AFTERNOON.

STILL EXPECT SOME ACCUMULATING SNOW OVER PARTS OF THE PANHANDLE THIS
EVENING AND OVERNIGHT WITH A DEVELOPING DEFORMATION AXIS AND MODEST
WRAP-AROUND MOISTURE. STILL LOOKS LIKE THE BEST SUPPORT WILL BE JUST
EAST OF THE CWA THOUGH...SO AMOUNTS WILL MOST LIKELY BE SUB ADVISORY
EXCEPT AT HIGHER ELEVATIONS ALONG THE PINE RIDGE. LATER SHIFTS WILL
NEED TO WATCH HOW THIS INTERACTS WITH HIGH WINDS THOUGH...AS TRAVEL
CONDITIONS MAY GET VERY NASTY. WINTER WEATHER ADVISORIES OR POSSIBLY
WINTER STORM WARNINGS MAY NEED TO BE CONSIDERED LATER ON IF IT LOOKS
LIKE WIDESPREAD SIGNIFICANT BLOWING SNOW WILL BE AN ISSUE. DAWES AND
BOX BUTTE COUNTIES WOULD PROBABLY SEE THE WORST CONDITIONS BASED ON
THE LATEST DATA. NOT THINKING PERSISTENT SNOW WILL BEGIN UNTIL AFTER
00Z TUE...SO WILL LET THE DAY SHIFT DECIDE HOW TO HANDLE THIS.

BROAD UPPER-LEVEL RIDGING IS FORECAST TO BUILD INTO THE AREA THROUGH
THE LATTER PART OF THE SHORT TERM PERIOD. DOWNSLOPE FLOW IS POSSIBLE
EAST OF THE LARAMIE RANGE ON WEDNESDAY WITH H7 TEMPS INCREASING TO
NEAR 0 DEG C. DESPITE THAT...WENT A FEW DEGREES BELOW GUIDANCE FOR
HIGHS AS SOME OF THE ENERGY WILL GO TOWARD MELTING SNOW. OBSERVED
TEMPERATURES WILL HEAVILY DEPEND ON HOW MUCH SNOW FALLS LATE TONIGHT
AND TUESDAY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 335 AM MST MON DEC 22 2014

FORECAST CHALLENGES WILL FOCUS ON POTENTIAL WINTER STORM SYSTEMS
IMPACTING THE CWA CHRISTMAS DAY/NIGHT AND LATE NEXT WEEKEND.

THE 00Z/06Z DETERMINISTIC MODEL GUIDANCE DEPICTS A SHORTWAVE RIDGE
QUICKLY TRANSLATING EAST FROM THE FRONT RANGE INTO THE GREAT PLAINS
WEDNESDAY NIGHT. THE NEXT PACIFIC TROUGH TRACKS EAST FROM THE
GREAT BASIN ACROSS THE ROCKIES LATE THURSDAY/EARLY FRIDAY. MODEL
DIFFERENCES BECOME APPARENT FRIDAY AS THE ECMWF AND CANADIAN GEM
HANG THE TROUGH FURTHER WEST WHILE THE GFS IS MORE PROGRESSIVE.
PRECIPITATION IS MORE WIDESPREAD WITH THE ECMWF WHILE THE GFS
LIMITS QPF OVER THE SOUTHEAST WY PLAINS AND SOUTHERN NE PANHANDLE
DUE TO THE DOWNSLOPE. MAINTAINED LIKELY POPS ALONG/WEST OF THE
LARAMIE RANGE WITH CHANCE POPS TO THE EAST. WINDS WILL BE
STRONGEST ALONG/WEST OF THE LARAMIE RANGE PRIOR TO FROPA WEDNESDAY
NIGHT/THURSDAY MORNING...THEN DECREASE DURING THE AFTERNOON. SNOW
ACCUMULATIONS WILL BE FAIRLY GENEROUS WITH THIS SYSTEM OVER THE
WEST...WITH UPWARDS OF A HALF FOOT FOR THE SNOWY/SIERRA MADRE AND
NORTH LARAMIE RANGES WITH 2 TO 4 INCHES LOWER ELEVATIONS.

AFTER THIS SYSTEM DEPARTS TO THE EAST...WEAK SHORTWAVE ENERGY AND
OROGRAPHICS WILL KEEP CHANCES FOR SNOW SHOWERS CONFINED TO THE
SOUTHERN MOUNTAINS FRIDAY/FRIDAY EVENING. SATURDAY WILL BE A
TRANSITION DAY WITH THE PASSAGE OF A SHORTWAVE RIDGE.
PRECIPITATION WILL SPREAD EAST INTO CENTRAL AND SOUTHERN WYOMING
/WEST OF A DOUGLAS TO LARAMIE LINE/ SUNDAY WITH THE ARRIVAL OF
ANOTHER PACIFIC TROUGH AND COLD FRONT.

HIGH TEMPERATURES CHRISTMAS DAY WILL RANGE FROM THE 20S AND 30S
NORTH AND WEST TO THE LOWER 40S SOUTHEAST. FRIDAY WILL BE COLDER
WITH HIGHS IN THE TEENS AND 20S. TEMPERATURES MODERATE SLIGHTLY
NEXT WEEKEND WITH 20S AND 30S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 335 AM MST MON DEC 22 2014

ACTIVE WINTER WEATHER PATTERN WILL CONTINUE THROUGH THE FORECAST
PERIOD. OCCASIONAL MVFR CEILINGS WILL BE POSSIBLE EAST OF THE
LARAMIE RANGE THIS MORNING...OTHERWISE EXPECT VFR CEILINGS AOA
5000 FT AGL. ALONG AND WEST OF THE LARAMIE RANGE WILL BE PERIODIC
MVFR TO IFR CEILINGS/VISIBILITIES IN SNOW SHOWERS. THE MOUNTAINS
WILL BE OBSCURED. GUSTY NORTHWEST WINDS OF 35 TO 45 KT WILL BE
COMMON TODAY AND TONIGHT...WITH AREAS OF BLOWING/DRIFTING SNOW
LIMITING VISIBILITIES AT TIMES IN THE VICINITY OF THE MOUNTAINS
AND HIGH VALLEYS. THERE IS A CHANCE FOR LIGHT SNOW TONIGHT ALONG
WITH OCCASIONAL MVFR CEILINGS/VISIBILITIES.

&&

.FIRE WEATHER...
ISSUED AT 429 AM MST MON DEC 22 2014

NO CRITICAL FIRE WEATHER OVER THE NEXT FEW DAYS. MOUNTAIN SNOW WILL
CONTINUE THROUGH TUESDAY WITH 2 TO 4 FEET OF TOTAL SNOW ACCUMULATION
IN THE SNOWIES AND SIERRA MADRES. WINDY CONDITIONS ARE EXPECTED EAST
OF THE LARAMIE RANGE TODAY...WITH STRONGER WINDS POSSIBLE LATE THIS
EVENING THROUGH TUESDAY MORNING. A WIND ADVISORY AND HIGH WIND WATCH
HAVE BEEN ISSUED FOR PARTS OF THE AREA. LIGHT SNOWFALL ACCUMULATIONS
ARE EXPECTED OVER THE PLAINS TONIGHT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ101-102-106>108-116>119.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST THIS MORNING FOR WYZ113-
     115.

     WINTER STORM WARNING UNTIL 8 AM MST THIS MORNING FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM THIS MORNING TO 5 PM MST THIS AFTERNOON
     FOR NEZ002-003-019>021-054-055-095-096.

     HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     NEZ019>021-054-055-095-096.

&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...MJ
FIRE WEATHER...CLH



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