Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 211259
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
559 AM MST FRI NOV 21 2014

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 559 AM MST FRI NOV 21 2014

AN ACTIVE PATTERN IS SHAPING UP FOR THE FORECAST AREA THIS
WEEKEND...WITH STRONG WINDS AND MOUNTAIN SNOWS THE MAIN FORECAST
CHALLENGES.

TODAY WILL BE ONE LAST RELATIVELY CALM WEATHER DAY AHEAD OF THE
MAIN PACIFIC STORM SYSTEM THAT WILL SLAM INTO THE PAC NW TODAY AND
MAKE A SOUTHEASTWARD TREK ACROSS THE ROCKIES THROUGH SUNDAY.
MILD...BREEZY AND DRY CONDITIONS WILL OCCUR TODAY IN THE WAKE OF A
WEAK SHORTWAVE TROUGH MOVING OVERHEAD THIS MORNING. FAIRLY STRONG
PRESSURE FALLS OF 4-8 MB/6 HR ARE PROGGED AHEAD OF THE PACIFIC
STORM SYSTEM TONIGHT...WHICH WILL RAPIDLY STRENGTHEN THE SFC
PRESSURE GRADIENT ACROSS SOUTHEAST WYOMING. THE CAG-CPR GRADIENT
LOOKS TO REACH THE MID 60 DAM READINGS BY SUNRISE...AND PEAK TO
MID 80 DAM VALUES BY MIDDAY SATURDAY. THE LLVL INVERSION LOOKS TO
RAPIDLY WEAKEN AND LIFT TO MOUNTAIN TOP LEVEL EARLY SATURDAY
MORNING AS WELL...SO FEEL CONFIDENT THAT THE HIGH WIND EVENT
WILL OCCUR FOR PORTIONS OF SOUTHEAST WYOMING. ISSUED A HIGH WIND
WATCH...STARTING FIRST IN THE ARLINGTON AND BORDEAUX ZONES BEFORE
SUNRISE WHICH ARE MOST SENSITIVE TO RAPID STRENGTHENING OF THE
GRADIENT AND DEVELOPMENT OF MOUNTAIN WAVE ACTIVITY...THEN
EXPANDING TO NORTHERN CARBON AND ALBANY COUNTIES AND THE SOUTHERN
LARAMIE RANGE. LOOKING AT THE POTENTIAL FOR 60 TO 70 MPH GUSTS FOR
THESE AREAS THROUGH THE DAY...WITH PERHAPS SLIGHTLY STRONGER GUSTS
IN THE MORE FAVORED GAP LOCATIONS OF ARLINGTON AND BORDEAUX.
THERE IS POTENTIAL FOR THE NEED TO EXPAND THIS HIGHLIGHT TO THE
NORTHERN LARAMIE RANGE AND WESTERN CONVERSE COUNTY AS WELL...AS
GUIDANCE IS SHOWING RATHER STRONG H7 WINDS IN EXCESS OF 65 KTS
OVER THE NORTHERN LARAMIES. CONFIDENCE IS A BIT LOWER IN THIS
SOLUTION...SO WILL HOLD OFF FOR NOW. THE PACIFIC FRONT WILL MOVE
WEST - EAST ACROSS THE FORECAST AREA AROUND SUNSET ON
SATURDAY...WITH STRONG BORA WINDS CONTINUING FOR A FEW MORE HOURS
BEFORE DIMINISHING OVERNIGHT. COULD SEE GUSTY NORTHWEST WINDS
EXPAND TO THE WYO/NEB PLAINS ON SUNDAY AFTERNOON...AND WILL NEED
TO MONITOR FOR FUTURE HIGHLIGHTS FOR THESE AREA OVER THE COMING
DAY. TEMPERATURES ON SATURDAY WILL BE QUITE MILD OVERALL IN THE
MID 40S TO UPPER 50S FROM WEST TO EAST WITH WAA AND DOWNSLOPE
WINDS IN PLACE...AND WILL COOL FOR SUNDAY BEHIND THE FRONT.

ALONG WITH THE STRONG WINDS...MODERATE TO HEAVY SNOW IS EXPECTED TO
DEVELOP IN THE MOUNTAINS OF SOUTHEAST WYOMING AS THE SYSTEM MOVES
THROUGH SATURDAY AFTERNOON THROUGH SUNDAY. LFQ JET DYNAMICS WILL
INCREASE SATURDAY AFTERNOON ALONG WITH MIDLEVEL PVA...PACIFIC
MOISTURE AND LLVL OROGRAPHIC EFFECTS WITH THE STRONG WINDS IN
PLACE. THE STRONGEST MIDLEVEL VORT MAX WILL TRAVERSE ACROSS THE
CWA SATURDAY NIGHT...WHILE THE JET DIVES SOUTH INTO AZ/NM. SO
EXPECT A HEAVY SNOW EVENT SATURDAY AFTERNOON AND NIGHT...WITH
ACCUMULATIONS AROUND ONE FOOT POSSIBLE IN THE SNOWY AND SIERRA
MADRES. COULD SEE A FEW INCHES AS WELL IN SURROUNDING VALLEYS.
BLOWING SNOW WILL BE A CONCERN WITH STRONG LLVL WINDS IN
PLACE...ALTHOUGH THEY WILL WEAKEN THROUGH THE NIGHT. THE MAIN JET
DYNAMICS WILL THEN REMAIN SOUTH OF OUR AREA ON SUNDAY AND MONDAY
ALTHOUGH MIDLEVEL ENERGY AND PACIFIC MOISTURE WILL CONTINUE TO
STREAM OVERHEAD THROUGH THIS TIME...SO EXPECT CONTINUED PERIODS OF
MODERATE TO HEAVY SNOW TO CONTINUE THROUGH SUNDAY AND MONDAY. WENT
AHEAD AND ISSUED A LONG DURATION WINTER STORM WATCH FOR THE
COMBINATION OF STEADY MODERATE/HEAVY SNOWFALL AND GUSTY WINDS THAT
ARE ANTICIPATED SATURDAY AFTERNOON THROUGH MONDAY FOR THE SNOWY
AND SIERRAS. THE HIGHEST SNOW TOTALS WILL BE ALONG WEST AND
NORTHWEST FACING SLOPES. FURTHER EAST...DOWNSLOPE WARMING AND
DRYING EFFECTS WILL SEVERELY LIMIT PRECIP CHANCES...ALTHOUGH CANT
RULE OUT A FEW SHOWERS IN THE LARAMIE RANGE AND EAST CENTRAL
WYOMING ESPECIALLY WITH THE MAIN PACIFIC FRONT SATURDAY NIGHT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 559 AM MST FRI NOV 21 2014

SUNDAY NIGHT/MONDAY...MOIST NORTHWEST FLOW ALOFT WILL PRODUCE
SCATTERED TO NUMEROUS SNOW SHOWERS OVER THE SNOWY AND SIERRA MADRE
RANGES...MAINLY DRY ELSEWHERE. WINDY PER PROGGED SURFACE THROUGH 700
MB GRADIENTS AND UNIDIRECTIONAL NORTHWEST WINDS.

TUESDAY...NORTHWEST FLOW ALOFT EVEN STRONGER...AND BASED ON
PROJECTED SURFACE THROUGH 700 MB HEIGHTS...SOME AREAS WILL LIKELY
SEE HIGH WIND CRITERIA. SLIGHT DECREASE IN MID LEVEL MOISTURE...THUS
SNOW COVERAGE ACROSS THE SNOWY AND SIERRA MADRE RANGES SHOULD BE
MORE LIMITED.

WEDNESDAY...ANOTHER QUITE WINDY DAY PER PROGGED SURFACE THROUGH 700
MB GRADIENTS. RELATIVELY MILD PER 850 MB AND 700 TEMPERATURES AND
DOWNSLOPE WARMING. ISOLATED TO SCATTERED SNOWS ACROSS OUR NORTHERN
COUNTIES FROM DOUGLAS TO LUSK TO CHADRON.

THANKSGIVING...THE MODELS ARE NOW SHOWING WEST NORTHWEST FLOW ALOFT
WITH OUR COUNTIES IN THE WARM SECTOR...ALONG WITH DOWNSLOPE WEST
WINDS. WILL BLEND WITH OUR NEIGHBORING OFFICE AND KEEP HIGH
TEMPERATURES DOWN...THOUGH LATER SHIFTS WILL NEED TO BETTER ASSESS
THE SITUATION.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 559 AM MST FRI NOV 21 2014

VFR PREVAILS. INCREASING CLOUD COVER THIS
AFTERNOON...WITH SCATTERED TO BROKEN CLOUDS AT OR ABOVE 9000 FEET
AGL.

&&

.FIRE WEATHER...
ISSUED AT 559 AM MST FRI NOV 21 2014

ONE LAST MILD...BREEZY AND DRY DAY IS EXPECTED FOR THE DISTRICT
TODAY. STRONG WINDS AND PERIODS OF SNOW WILL OCCUR IN AND NEAR THE
MOUNTAINS OF SOUTHEAST WYOMING THROUGH MIDDLE OF NEXT WEEK. WINDY
CONDITIONS WILL EXPAND TO THE PLAINS ON SUNDAY AND WILL CONTINUE
THROUGH MIDWEEK AS WELL

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY
     AFTERNOON FOR WYZ112-114.

     HIGH WIND WATCH FROM SATURDAY MORNING THROUGH SATURDAY EVENING
     FOR WYZ104-105-116-117.

     HIGH WIND WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING FOR
     WYZ106-110.

NE...NONE.
&&

$$

SHORT TERM...RJM
LONG TERM...SAR
AVIATION...SAR
FIRE WEATHER...RJM


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