Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 251944
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1244 PM MST TUE NOV 25 2014

.UPDATE...
ISSUED AT 1244 PM MST TUE NOV 25 2014

STRONG WINDS HAVE DEVELOPED THIS MORNING AS EXPECTED ACROSS
PORTIONS OF SOUTHEAST WYOMING. HIGHEST WINDS RECORDED SO FAR
OCCURRED IN THE ARLINGTON AREA BETWEEN 4 AND 8 AM...WITH GUSTS
RANGING FROM 65 TO 80 MPH. 55 TO 65 MPH GUSTS WERE COMMON
ELSEWHERE WITHIN THE WARNING. ALSO NOTICED KSAA APPROACHING HIGH
WIND CRITERIA...SO ADDED IN THE UPPER NORTH PLATTE RIVER VALLEY TO
THE HIGH WIND WARNING. WINDS HAVE SETTLED A BIT SINCE EARLIER
ON WITH SPEEDS AVERAGING MORE 55 TO 65 MPH. SHOULD SEE THESE
SPEEDS CONTINUE THROUGH THE EVENING AS FULL MIXING POTENTIAL IS
REALIZED...WITH PERHAPS A SLIGHT BUMP UP IN SPEEDS EARLY THIS
EVENING AS THE COLD FRONT APPROACHES FROM THE NORTH. THE COLD
FRONT WILL PASS SOUTH THROUGH THE PLAINS BY 03Z AND WILL STALL
ALONG THE LARAMIE RANGE...RELAXING THE GRADIENT SUFFICIENTLY TO
DIMINISH WINDS ACROSS THE AREA. HOWEVER...THINK THE LULL IN SPEEDS
WILL BE BRIEF OUT AT ARLINGTON AND EXPECT SPEEDS TO INCREASE ONCE
AGAIN AS SUNRISE APPROACHES. IN ADDITION...THE FRONT WILL SHIFT
EAST THROUGH THE MORNING AND WILL RESTRENGTHEN THE LLVL PRESSURE
GRADIENT...WHICH IS FAVORABLE FOR GAP WINDS TO REDEVELOP IN THIS
AREA. SO WENT AHEAD AND EXTENDED THE HIGH WIND WARNING FOR THE
ARLINGTON AREA THROUGH TOMORROW AFTERNOON. MAY HAVE TO REVISIT
WIND HIGHLIGHTS FOR THE SOUTHERN LARAMIE RANGE AND BORDEAUX AS
WELL...BUT CONFIDENCE IS NOT HIGH ENOUGH THAT HIGH WINDS WILL BE
REALIZED AT THIS TIME.

SURFACE AND RADAR TRENDS OVER THE PAST FEW HOURS OVER NORTHERN
WYOMING SYNC UP FAIRLY WELL WITH GUIDANCE REGARDING SNOW
POTENTIAL FOR THIS EVENING AND OVERNIGHT PERIOD ACROSS THE EASTERN
PLAINS. BASED ON CONSISTENT PROGS FOR FRONTOGENESIS AND NEGATIVE
EPV ABOVE THE FRONTOGENESIS BAND...UPSLOPE FLOW BEHIND THE
FRONT...AND SUFFICIENT MOISTURE LINING UP NW-SE FROM THE SOUTHERN
LARAMIE RANGE TO EASTERN LARAMIE COUNTY...FEEL CONFIDENT IN THE
POTENTIAL FOR NW-SE ORIENTED SNOW BANDS TO DEVELOP AFTER AROUND
02Z THIS EVENING AND PERSISTING OVERNIGHT IN THIS AREA. INITIAL
DEEP OMEGA AS THE FRONTOGENESIS BAND INTENSIFIES WILL WANE
OVERNIGHT AS SUBSIDENCE IN THE RFQ OF THE UPPER JET MOVES
OVERHEAD...SO WILL LIMIT SNOW ACCUMULATIONS TO 2 TO 5 INCHES ON
AVERAGE WITH LOCALLY HIGHER AMOUNTS DEPENDING ON WHERE EXACTLY THE
BAND SETTLES. THUS...WENT AHEAD WITH A WINTER WEATHER ADVISORY FOR
SOUTHERN PLATTE COUNTY...CENTRAL AND EASTERN LARAMIE COUNTIES.
CURRENT PROGS EVENTUALLY SETTLE THE SNOW BAND SOUTH OF GOSHEN
COUNTY SO WILL KEEP IT OUT OF THE ADVISORY FOR NOW.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY NIGHT)
ISSUED AT 410 AM MST TUE NOV 25 2014

AN ACTIVE PERIOD TAKING ACROSS THE CWA BEGINNING WITH A PERIOD OF
VERY STRONG WINDS ACROSS SOUTHEAST WYOMING TODAY FOLLOWED BY SOME
LIGHT TO MODERATE SNOW TONIGHT. LETS FIRST FOCUS ON HIGH WINDS
TODAY. 10Z SFC ANALYSIS SHOWS LOW 1006MB LOW PRESSURE LOCATED OVR
SW SASKATCHEWAN WITH AN AMPLIFYING PRESSURE TROUGH EXTENDING SOUTH
ALONG THE FRONT RANGE. KCAG-KCPR GRADIENT ALREADY AT AROUND 13MB
AT THIS HOUR. WINDS HAVE COME UP IN THE ARLINGTON AREA RIGHT ON
TIME BETWEEN 08-09Z WHERE GUSTS HAVE BEEN HOVERING AROUND 60 MPH.
MEANWHILE AT H3...THE FAVORABLE SUBSIDING RFQ OF 160 KNOT
ANTICYCLONIC JET WAS JUST ENTERING WRN ZONES EARLY THIS MORNING.
SUBSIDENCE COMBINED WITH H7 PROGS OF 50-70 KNOTS AND KCAG-KCPR
LLVL HEIGHT GRADIENTS OF 60-90 METERS WILL BE MORE THAN ENOUGH FOR
WIDESPREAD GUSTS OF 60+ MPH GUSTS TODAY. THE ONE LIMITING FACTOR
MAY BE JUST HOW MUCH THICKER CLOUD COVER LESSENS LLVL MIXING.
MORNING SATELLITE PIX SHOWS A THICK SLUG OF MOISTURE DROPPING
SOUTHEAST INTO THE AREA. SUSPECT THAT THE TYPICAL WIND PRONE AREAS
WILL HAVE NO PROBLEM SEEING THESE WINDS. HOWEVER...WOULD NOT BE
SURPRISED IF ERN LARAMIE COUNTY STRUGGLES A BIT TO GET THERE.
ALTHOUGH LLVL GRADIENTS DROP OFF SOMEWHAT TONIGHT...THEY STILL
REMAIN ABOVE 60 METERS THRU MIDDAY WEDNESDAY. WOULD NOT BE
SURPRISED IF THE HIGH WIND WARNING NEEDS TO BE EXTENDED INTO
WEDNESDAY MORNING AT LEAST FOR THE ARLINGTON AREA.

THE OTHER FORECAST FOCUS IS THE POTENTIAL FOR SNOW TODAY MAINLY
WEST OF THE LARAMIE RANGE AND TONIGHT ON THE ERN PLAINS OF SE
WYOMING. THE CULPRIT IS A CLIPPER SYSTEM THAT WAS DIVING SOUTHEAST
OUT OF ALBERTA THIS MORNING AND IS PROGD TO REACH THE DAKOTAS BY
SUNSET. AS IT DOES SO...COLD FRONT WILL DROP SOUTH LATE TODAY AND
BECOME STATIONARY ALONG THE LARAMIE RANGE TONIGHT. AREA OF
NEGATIVE EPV BECOMES CO-LOCATED JUST ABOVE THE LLVL SFC FRONT TO
BECOME FAVORABLE FOR THE DEVELOPMENT OF NW/SE ORIENTED SNOW BAND
TONIGHT. HAVE BOOSTED SNOW CHANCES TO ACCOUNT FOR THE INCREASED
CONFIDENCE IN SNOW BANDING TONIGHT. MOST AREAS OF THE SOUTHEAST
WYOMING PLAINS WILL SEE 1 TO 3 INCHES TONIGHT...WITH LOCALLY UP TO
4 OR 5 INCHES POSSIBLE PENDING WHERE THE SNOW BAND SETS UP...WHICH
MODELS HAVE NOW ACROSS LARAMIE COUNTY. THINK THAT AN ADVISORY WILL
BE NECESSARY WHEREVER THIS BAND SETS UP...BUT WILL LET THE DAY
SHIFT TAKE ONE MORE LOOK AT 12Z DATA BEFORE MAKING THAT CALL.
OTHERWISE...THE HEAVY SNOW WILL CONTINUE INTO THE SNOWY/SIERRA
MADRE RANGES THRU TONIGHT WITH AN ADDL FOOT OF SNOW EXPECTED
THERE. WILL KEEP THE WINTER STORM WARNING GOING AS INHERITED.

A LESS EVENTFUL DAY IN STORE ON WEDNESDAY...THOUGH BREEZY TO LOCALLY
WINDY CONDITIONS WILL CONTINUE WEST OF THE LARAMIE RANGE. COLD
FRONT WILL RETREAT EAST DURING THE DAY...BUT NOT BEFORE AREAS EAST
OF A LUSK TO BRIDGEPORT LINE ONLY REACH THE 30S FOR HIGHS.
ELSEWHERE EXPECT HIGH TEMPERATURES TO REACH THE 40S ON WEDNESDAY.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 410 AM MST TUE NOV 25 2014

TEMPS WILL BE QUITE WARM FOR LATE NOV FROM THANKSGIVING THROUGH
SATURDAY. A LEE TROUGH WILL PROMOTE GOOD DOWNSLOPE FLOW IN THE
LLVLS AND COMBINE WITH 700MB TEMPS OF 1-3C. MOS GUIDANCE HAS THE
WARMEST TEMPS ON FRI WHEN MANY AREAS TO THE EAST OF THE LARAMIE
RANGE WILL BE IN THE UPPER 50S TO LOW 60S. THE CAG-CPR GRADIENT
WILL REMAIN BETWEEN 50 AND 60 METERS FROM THURS INTO MIDDAY SAT
SO WINDY CONDITIONS WILL PERSIST OVER SOUTHEAST WY AND ESPECIALLY
THE WIND PRONE AREAS. COULD SEE A PROLONGED PERIOD OF TWO DAYS
WHERE PLACES LIKE ARLINGTON WILL BE BOUNCING AROUND HIGH WIND
CRITERIA. SHORTWAVE PUSHES SOUTHWARD TO ALONG THE CANADIAN BORDER
ON SAT WITH A SFC HIGH MOVING INTO MONTANA. HIGHER PRESSURES
ACROSS THE PLAINS WILL EFFECTIVELY END THE HIGH WIND THREAT OVER
SOUTHEAST WY BY LATE SAT.  THE GFS SHOWS A COLD FRONT BACKING
ACROSS THE PLAINS ON SAT NIGHT WHEREAS THE ECMWF IS HAS A STRONGER
FRONTAL PUSH AND ASSOCIATED COLD AIR ADVECTION. WENT WITH ABOUT A
15 DEGREE COOLDOWN FOR SUN...BUT THE COLDER ECMWF WOULD JUSTIFY A
BIGGER DROP. CHANCES FOR PRECIP WILL BE MINIMAL BEHIND THE FRONT
AS UPPER LEVEL SUPPORT IS LACKING. TEMPS WILL LIKELY BEGIN TO
MODERATE ON MON AS A TROUGH AMPLIFIES ALONG THE WEST COAST.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1029 AM MST TUE NOV 25 2014

STRONG WEST WINDS WILL CONTINUE TO BE THE MAIN AVIATION HAZARD
ACROSS SOUTHEAST WYOMING THROUGH THE AFTERNOON. WINDS COULD GUST
AS HIGH AS 55 KTS OVER THE NEXT SEVERAL HOURS WITH MOUNTAIN WAVE
ACTIVITY RESULTING IN POTENTIALLY SEVERE LOW-LEVEL TURBULENCE. A
HIGH WIND WARNING IS IN EFFECT. AREAS OF BLOWING SNOW WILL ALSO BE
POSSIBLE THROUGH THE DAY. SNOW WILL DEVELOP AFTER 23Z AND CONTINUE
THROUGH THE NIGHT...MAINLY ALONG AND SOUTHWEST OF A LINE FROM DGW
TO BFF. IFR VSBYS CAN BE EXPECTED IN -SN AND BLSN.

&&

.FIRE WEATHER...
ISSUED AT 410 AM MST TUE NOV 25 2014

MINIMAL FIRE WEATHER CONCERNS IN THE FORESEEABLE FUTURE. A BREEZY
TO LOCALLY WINDY DAY AHEAD ACROSS THE DISTRICTS TODAY WITH WIND
GUSTS OF 60 TO 70 MPH EXPECTED ACROSS MUCH OF SOUTHEAST WYOMING. A
PERIOD OF SNOW WILL FALL TONIGHT WITH ACCUMULATIONS OF 1 TO 3
INCHES EXPECTED ACROSS LOWER ELEVATIONS IN SOUTHEAST WYOMING. THE
SNOWY AND SIERRA MADRE RANGES WILL SEE UP TO ANOTHER FOOT OF SNOW
THROUGH TONIGHT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 7 AM MST WEDNESDAY FOR WYZ112-114.

     HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING FOR WYZ104>106-
     109-116-117.

     HIGH WIND WARNING UNTIL 2 PM MST WEDNESDAY FOR WYZ110.

     WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM MST
     WEDNESDAY FOR WYZ106-107-117>119.

     HIGH WIND WARNING UNTIL 7 PM MST THIS EVENING FOR WYZ107-113-115-
     118-119.

NE...NONE.
&&

$$

UPDATE...RJM
SHORT TERM...CAH
LONG TERM...ZF
AVIATION...CLH
FIRE WEATHER...CAH



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