Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 191111
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
411 AM MST FRI DEC 19 2014

.SHORT TERM...(TODAY AND SUNDAY NIGHT)
ISSUED AT 400 MST FRI DEC 19 2014

SHORTWAVE ENERGY EMBEDDED WITHIN NORTHWEST FLOW MOVING THRU WYOMING
EARLY THIS MORNING HAS BEEN DOING LITTLE MORE THAN BOOSTING WIND
GUSTS TO 35-45 MPH THRU THE WIND CORRIDOR AND PRODUCING SOME LIGHT
SNOW IN THE SNOWY/SIERRA MADRES. THIS SHORTWAVE WILL DEPART THE AREA
BY EARLY AFTERNOON ALLOWING FOR A WEAKENING TRANSITORY RIDGE
TONIGHT. CLOUDS SHOULD REMAIN TUCKED CLOSE TO THE HIER TERRAIN
TODAY...WITH MOSTLY/PARTLY SUNNY SKIES ELSEWHERE. BREEZY CONDITIONS
WILL RETURN TODAY AS WELL IN AND AROUND THE SOUTHEAST WYOMING
MOUNTAINS AND ADJACENT PLAINS. THE GOOD NEWS IS THAT THESE WINDS
SHOULD BOOST TEMPS A FEW DEGREES IN THE IMMEDIATE LEE...LIKELY INTO
THE LOWER 40S TODAY.

THE PATTERN TURNS WEST/NORTHWEST AND STRENGTHENS ON SATURDAY AS A
180+ KNOT ZONAL JET PLOWS INTO THE PACNW. ALTHOUGH THE CWFA WILL
REMAIN GENERALLY DRY FOR SATURDAY...SNOW CHANCES WILL BEGIN RAMP UP
OVER THE SNOWY/SIERRA MADRES AS THE PACIFIC MOISTURE FETCH BEGINS TO
BE TAPPED. ANOTHER BREEZY DAY CAN BE EXPECTED ON SATURDAY...WHICH
WILL AGAIN HELP BOOST HIGHS INTO THE LOW/MID 40S OUT ON THE ERN
PLAINS.

IMPACTS WILL BEGIN TO BECOME MORE APPARENT LATE SATURDAY NIGHT AND
DURING THE DAY ON SUNDAY AS THE WIND MACHINE AND THE BEGINNING OF A
LONG DURATION MOUNTAIN SNOW EVENT ENSUES. LETS FOCUS ON THE WIND
IMPACTS FIRST. LLVL KCAG-KCPR GRADIENTS INCREASE ABOVE CRITICAL
THRESHOLDS BEGINNING AROUND 09Z SUNDAY CONTINUING THRU THE DAY.
PROGD AXIS OF LLVL SUBSIDENCE WILL IMPACT THE WIND CORRIDOR. SO HAVE
OPTED TO ISSUE A HIGH WIND WATCH EFFECTIVE FOR ARLINGTON/BORDEAUX
07Z 12/21 THRU 07Z 12/22. INCLUDED THE SRN LARAMIE RANGE 16Z 12/21
THRU 07Z 12/22. THE OTHER IMPACT THAT WILL BEGIN TO BE FELT LATE
SATURDAY NIGHT AND MORESO DURING THE DAY ON SUNDAY AND SUNDAY WILL
BE A SIGNIFICANT SNOW EVENT FOR THE WEST SLOPE. MODELS ARE VERY
CONSISTENT IN 40-50 KNOTS OF LLVL WEST FLOW ADVECTING COPIOUS
AMOUNTS OF PACIFIC MOISTURE INTO THE SNOWY/SIERRA MADRE RANGES.
WOULD NOT AT ALL BE SURPRISED TO SEE 1-2 FEET OR MORE OF SNOW IN
THOSE AREAS LATE SATURDAY NIGHT THROUGH THE DAY ON MONDAY. HIGH
TEMPERATURES WILL AGAIN IN THE 30S WEST OF THE LARAMIE RANGE ON
SUNDAY...WITH 40S EAST.

.LONG TERM...(MONDAY THROUGH THURSDAY)
ISSUED AT 400 AM MST FRI DEC 19 2014

WITH MOIST NORTHWESTERLY FLOW ALOFT IN PLACE ON MON AND THE UPPER
LEVEL JET TO THE WEST OF THE CWA...SNOW WILL CONTINUE ACROSS THE
SIERRA MADRE AND SNOWY RANGES. COULD ALSO SEE A BRIEF SHOT OF
LIGHT SNOW OVER LOWER ELEVATIONS BEHIND A MON MORNING COLD FRONT.
WINDY CONDITIONS WILL SPREAD ACROSS THE PLAINS INCLUDING THE
WESTERN NEBRASKA PANHANDLE ON MON WITH STEEPENING LLVL LAPSE RATES
AND COLD AIR ADVECTION. THE GFS IS STRONGER WITH THE WINDS ALOFT
BUT ALL MODELS SHOW GOOD LLVL MIXING. PRECIP WILL COME TO AN END
ACROSS THE MTNS BY TUES MORNING AS THE JET SHIFTS EASTWARD AND
DRYING OCCURS. TRANSITORY RIDGE MOVES OVERHEAD FOR WED.  IT WILL
BE CHILLY EARLY NEXT WEEK ESPECIALLY WHEN YOU FACTOR IN THE
WIND...WITH SLIGHT WARMING BY WED.

ATTENTION THEN TURNS TO THE LONGWAVE TROUGH THAT IS PROGGED TO
DROP SOUTHEASTWARD FROM THE PACIFIC NW INTO THE INTERMOUNTAIN WEST
BY LATE WED INTO THURS. THE GFS AND ECMWF ARE IN PRETTY GOOD
AGREEMENT AND SHOW THE TROUGH AXIS NEAR UTAH BY 18Z THURS. UPPER
LEVEL DIVERGENCE AND LARGE SCALE ASCENT WOULD SPREAD ACROSS THE
CWA BY THURS AFTN INTO THURS NIGHT. PRECIP DEVELOPS BEHIND THE
FROPA AND MODELS ARE CURRENTLY SHOWING WIDESPREAD QPF AMOUNTS OF
0.2-0.5 INCHES. IT IS A RATHER PROGRESSIVE SYSTEM WITH SNOW COMING
TO AN END BY FRI MORNING. WILL CONTINUE TO MONITOR THE EVOLUTION
OF THIS SYSTEM WITH THE HOLIDAY APPROACHING.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 400 AM MST FRI DEC 19 2014

VFR CONDITIONS THROUGH THE TAF PERIOD. WEST WINDS WILL INCREASE BY
LATE MORNING ACROSS SOUTHEAST WY AND WILL REMAIN BREEZY THROUGH
THE AFTERNOON WITH OCCASIONAL GUSTS TO 25-30 MPH. THE WINDS WILL
THEN COME DOWN SOMEWHAT AFTER SUNSET. CLOUD COVER WILL BE LIMITED
TO MAINLY PASSING HIGH CLOUDS.

&&

.FIRE WEATHER...
ISSUED AT 350 AM MST FRI DEC 19 2014

NO FIRE WEATHER CONCERNS THROUGH THE PERIOD. BREEZY BUT GENERALLY
DRY CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS TODAY AND
TOMORROW. HIGH TEMPERATURES WILL REACH THE 30S AT MOST PLACES WITH
SOME 40S OUT ON THE EASTERN PLAINS. WINDY CONDITIONS AND
SIGNIFICANT MOUNTAIN SNOW ACCUMULATIONS RETURN BEGINNING SATURDAY
NIGHT AND CONTINUING INTO EARLY NEXT WEEK. HIGH WIND WATCHES HAVE
BEEN POSTED FOR PORTIONS OF SOUTHEAST WYOMING. MEANWHILE...WINTER
STORM WATCHES HAVE BEEN ISSUED FOR THE SNOWY AND SIERRA MADRE
RANGES WHERE 1 TO 2 FEET OF SNOW WILL BE POSSIBLE.

&&

.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.
&&

$$

SHORT TERM...CAH
LONG TERM...ZF
AVIATION...ZF
FIRE WEATHER...CAH



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