Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 212245
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
345 PM MST FRI NOV 21 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 345 PM MST FRI NOV 21 2014

QUIET WEATHER IS QUICKLY COMING TO AN END AS WE TRANSITION INTO A
VERY ACTIVE PATTERN FOR THE SHORT TERM PERIOD. HIGHLIGHTS REVOLVE
AROUND POTENTIAL FOR VERY STRONG WINDS OVER SOUTHEAST WYOMING AND
POSSIBLY WESTERN NEBRASKA...AND MOUNTAIN SNOWS. LATEST WATER VAPOR
SATELLITE LOOP SHOWS A VIGOROUS UPPER-LEVEL SHORTWAVE JUST ABOUT TO
CRASH INTO THE PACIFIC NORTHWEST THIS EVE. OBJECTIVE UPPER ANALYSIS
SHOWS A STRONG 110+ KT JET CORE OFFSHORE AT 21Z. THIS WILL BE OUR
MAJOR WEATHER MAKER OVER THE NEXT COUPLE OF DAYS AS THE SYSTEM MOVES
RAPIDLY SOUTHEAST AND STRENGTHENS. NOT EXPECTING ANYTHING MAJOR IN
THE NEAR TERM THOUGH. SHOULD BE A QUIET EVENING WITH WINDS STARTING
TO RELAX AS MIXING DWINDLES WITH THE LOSS OF AFTN HEATING. A BROAD
AREA OF SURFACE HIGH PRESSURE WILL KEEP THINGS ON THE DRY SIDE.

THINGS CHANGE QUICKLY INTO TONIGHT. THE NAM H85 CAG-CPR GRADIENT IS
PROGGED TO CLIMB ABOVE 60 METERS BY ABOUT 09Z SAT. MODELED LLVL FLOW
IS IMPRESSIVE TO SAY THE LEAST WITH AN EXTENSIVE CORE OF 60 TO 70 KT
WINDS BETWEEN 700 AND 800 MILLIBARS OVER A GOOD CHUNK OF OUR WYOMING
ZONES BY SUNRISE. WITH EXCELLENT SUBSIDENCE OVER THE TRADITIONAL GAP
AREAS AND GOOD 6-HR PRESSURE FALLS ON THE ORDER OF 5-10 MB PER THE
GFS...CONFIDENCE IS HIGH IN A WIDESPREAD AND POTENTIALLY SIGNIFICANT
WIND EVENT. WENT AHEAD AND UPGRADED TO A HIGH WIND WARNING WITH ALL
ZONES STARTING AT 09Z. ARL AND BRX SHOULD HIT FIRST...WITH THE WIND
CORE ALOFT SPREADING INTO THE SOUTHERN LARAMIE RANGE/FOOTHILLS AT OR
AROUND SUNRISE. ADDED THE NORTHERN LARAMIE RANGE TO THE WARNING AS
WELL AS BOTH THE GFS AND NAM SHOW 65 KT WINDS AT H75 TO THE SOUTH OF
DEER CREEK IN WESTERN CONVERSE COUNTY. THIS MAY BE QUITE THE EVENT
WITH MULTIPLE GUSTS OVER 70 MPH. ANOTHER EVENTUAL CONCERN IS THE
POTENTIAL FOR LIGHT SNOW WEST OF THE LARAMIE RANGE LATER IN THE
AFTERNOON AND EVENING. WITH STRONG WINDS WILL COME THE POTENTIAL FOR
SIGNIFICANTLY REDUCED VISIBILITIES IN BLOWING SNOW EVEN THOUGH LOWER
ELEVATIONS SHOULD NOT SEE MUCH FOR ACCUMULATIONS. MADE IT A POINT TO
MENTION THIS IN THE NPW PRODUCT.

SOMEWHAT CONCERNED THAT SOME OF THE ADJACENT VALLEYS AND HIGH PLAINS
MAY GET IN ON SOME OF THE WINDY FUN TOMORROW AS WELL. THERE ARE SOME
KEY DIFFERENCES IN THE GFS AND NAM WHICH WILL HAVE A ROLE IN WHETHER
OR NOT WE SEE WARNING CRITERIA WINDS AT AREAS SUCH AS CHEYENNE AND
THE LARAMIE VALLEY. FORECAST SOUNDINGS FROM BOTH MODELS SHOW A BELT
OF VERY STRONG FLOW NOT FAR OFF THE SURFACE. THE DIFFERENCES ARE IN
THE MIXING. MAIN LIMITING FACTOR WILL BE CLOUD COVER...BUT BOTH THE
LOW AND MIDLVL RH FIELDS DO NOT SUGGEST ANYTHING THICK ENOUGH. COULD
EVENTUALLY SEE AN ABUNDANCE OF LENTICULARS EAST OF THE MOUNTAINS AS
MOUNTAIN WAVE ACTIVITY BECOMES INTENSE IN THE AFTN. IF THIS DOES NOT
IMPACT SURFACE HEATING...GFS SOUNDINGS SUGGEST 50-60 KTS AT THE TOP
OF THE MIXED LAYER AT LARAMIE AND CHEYENNE. THE NAM IS CONSIDERABLY
LESS...HOWEVER IT DOES SHOW SUBSIDENCE IN ITS OMEGA FIELDS SPREADING
SLOWLY ONTO THE PLAINS BETWEEN 18-00Z. DECIDED TO ISSUE A HIGH WIND
WATCH FOR LOWER ELEVATIONS IMMEDIATELY ADJACENT TO THE LARAMIE RANGE
AND FOOTHILLS. EVEN IF AFTERNOON MIXING IS NOT THE CULPRIT...MODELS
ARE IN GOOD AGREEMENT WITH A TRANSITION TO A BORA WIND EVENT ON SAT
NIGHT THROUGH EARLY SUN AS A COLD FRONT SWEEPS ACROSS THE CWA. COULD
SEE WIND GUSTS RAMP UP AGAIN FOR A FEW HOURS AROUND MIDNIGHT...WITH
A FEW GUSTS TO 60 MPH POSSIBLE OVERNIGHT.

SUNDAY WILL BE VERY WINDY OVER THE PLAINS OF SOUTHEAST WYOMING AND
THE WESTERN PANHANDLE. THE CWA WILL BE IN THE POST FRONTAL AIR MASS
AND THE MODELS SHOW A RIBBON OF 60 TO 70 KTS FROM NEAR LSK SOUTHEAST
TOWARD SNY AT 00Z MON. WILL LIKELY NEED MORE WIND HEADLINES FOR THIS
TIME FRAME...BUT WILL GET THROUGH THE SATURDAY EVENT FIRST. NOW THAT
THE WIND DISCUSSION IS OUT THE WAY...ONTO THE SNOW POTENTIAL. DIDNT
MAKE ANY CHANGES TO THE WINTER STORM WATCH FOR THE MOUNTAINS...BUT
IT STILL LOOKS GOOD. FIREHOSE OF AN UPPER JET WITH 150+ KT H25 CORE
IS PROGGED TO REMAIN ANCHORED OVER THE WESTERN US FOR SEVERAL DAYS
WITH OUR MOUNTAINS REMAINING IN THE FAVORED LEFT EXIT REGION. THIS
COMBINED WITH FAVORABLE OROGRAPHICS IN WEST-NORTHWEST FLOW AND AND
SEVERAL REINFORCING SHOTS OF 700-300 MILLIBAR MOISTURE EMBEDDED IN
THE ACTIVE FLOW ALOFT WILL SUPPORT PERIODS OF HEAVY SNOW. SHOULD SEE
ONE OR TWO FEET THROUGH MON WITH ADDITIONAL SNOW POSSIBLE IN THE
DAYS FOLLOWING. SHOULD BE PRIMARILY A MOUNTAIN EVENT WITH AREAS EAST
OF THE LARAMIE RANGE STAYING DRY IN DOWNSLOPING LLVL FLOW. MAY SEE A
FEW RAIN OR SNOW SHOWERS OVER THE NORTHERN PANHANDLE ON SUN AFTN AS
PVA OVERSPREADS THE AREA.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 345 PM MST FRI NOV 21 2014

BASED ON GFS/ECMWF MODEL SOLUTIONS...SHOULD SEE A BREAK IN SNOW
ACCUMULATIONS OVER SOUTHEAST WYOMING MOUNTAINS SUNDAY EVENING WITH
A SHORTWAVE RIDGE IN PLACE. THEN THE NEXT SHOT OF SNOW LIKELY TO
DEVELOP AFTER MIDNIGHT SUNDAY NIGHT. COULD SEE SOME LIGHT SNOW
INTO LOWER ELEVATIONS BUT MOST SNOW ACCUMULATIONS WILL GENERALLY
BE IN THE MOUNTAINS. VERY LITTLE CHANCE FOR ANY ACCUMULATIONS
EAST OF THE LARAMIE RANGE SUNDAY NIGHT THROUGH MONDAY. WINDS WILL
SUBSIDE ACROSS MOST OF THE AREA SUNDAY NIGHT BUT ANOTHER PUSH OF
STRONGER WINDS POSSIBLE MONDAY NIGHT AS ANOTHER STRONG UPPER LEVEL
JET MOVES OVER THE AREA. MAIN CONCERN FOR HIGH WINDS WILL BE OVER
THE FAVORED WIND PRONE LOCATIONS IN SOUTHEAST WYOMING SUCH AS
ARLINGTON...BORDEAUX AND THE SOUTHERN LARAMIE RANGE.

THE NEXT QUICK MOVING CLIPPER SYSTEM ALONG WITH THE UPPER JET
WILL BRING A CHANCE FOR LIGHT SNOW SHOWERS THROUGH TUESDAY
AFTERNOON...INCLUDING INTO THE NEBRASKA PANHANDLE. AT THIS TIME
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATIONS...IF ANY. MAINLY
LOOKING FOR LIGHT SNOW SHOWERS AND FLURRIES.

UNCERTAINTLY REMAINS FOR LATER PORTIONS OF THE WEEK AND HOLIDAY
WEEKEND GIVEN THE GFS AND ECMFW WERE COMPLETELY DIFFERENT IN
THEIR SOLUTIONS YESTERDAY. HOWEVER...BOTH MODLES TRENDED TOWARD
EACH OTHER TODAY AND HAVE RATHER SIMILAR SOLUTIONS. WOULD LIKE TO
SEE RUN OR TWO OF CONSISTENCY BUT BASED ON LATEST SOLUTIONS IT
WOULD WARM BOTH THURSDAY AND FRIDAY WITH A FLATTENING RIDGE OVER
THE NORTHERN ROCKIES PRODUCING DOWNSLOPE WARMING. INTO THE
WEEKEND THE MODLES SUGGEST A FAST MOVING BUT RELATIVELY WEAK WAVE
MOVING ACROSS THE AREA...SO NO BIG HAZARDOUS WEATHER THREAT
EXPECTED AT THIS TIME.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 234 PM MST FRI NOV 21 2014

AVIATION CONCERNS TO MAINLY FOCUS ON WINDS LATE TONIGHT AND INTO
TOMORROW AND SNOW WHICH WILL DEVELOP OVER THE MOUNTAINS TOMORROW
AFTERNOON. STRONG WINDS WITH FREQUENT GUSTS TO 50 KTS AND GREATER
WILL DEVELOP IN THE ARLINGTON AREA AND INTO THE BORDEAUX AREA
LATE TONIGHT. THESE STRONG WEST TO SOUTHWEST WINDS WILL THEN
SPREAD INTO THE SOUTHERN AND NORTHERN LARAMIE RANGES TOWARD
SUNRISE SATURDAY. GUSTY WINDS WILL ALSO SPREAD INTO LOWER
ELEVATIONS AND INTO THE PLAINS OF SOUTHEAST WYOMING SATURDAY
AFTERNOON WITH GUSTS OF 30 TO 40 KTS BEING COMMON. WINDS WILL NOT
BE AS STRONG INTO THE NEBRASKA PANHANDLE BUT STILL BREEZY TO WINDY
SATURDAY AFTERNOON.

MOUNTAINS WILL BE OBSCURED DUE TO FALLING AND BLOWING SNOW
SATURDAY AFTERNOON...ESPECIALLY INTO THE SNOWY AND SIERRA MADRE
RANGES WHERE A WINTER STORM WATCH IS CURRENTLY IN EFFECT. PERIODS
OF SNOW WILL CONTINUE INTO MONDAY ACROSS THESE MOUNTAINS.

STRONG NORTHWEST WINDS EXPECTED OVER THE NEBRASKA PANHANDLE SUNDAY
WITH STRONGER WINDS ALSO POSSIBLE INTO SOUTHEAST WYOMING.

&&

.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 WARNING FROM 2 AM SATURDAY TO 5 AM MST SUNDAY FOR
     WYZ103>106-110-116-117.

     HIGH WIND WATCH FROM SATURDAY MORNING THROUGH LATE SATURDAY
     NIGHT FOR WYZ101-107-115-118.

NE...NONE.

&&

$$

SHORT TERM...CLH
LONG TERM...SML
AVIATION...SML
FIRE WEATHER...RJM


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