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000
FXUS65 KCYS 030554
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1054 PM MST MON DEC 2 2013

.UPDATE...
ISSUED AT 1045 PM MST MON DEC 2 2013

WINDS HAVE CONTINUED TO DECREASE ACROSS THE CWFA...SO HAVE
CANCELLED THE HIGH WIND WARNING FOR THE ENTIRE AREA. ARCTIC
BOUNDARY IS ROUGHLY LOCATED FROM JEFFREY CITY TO JUST NORTH OF
CASPER TO NORTH OF WRIGHT. MANY OBSERVATION SITES ACROSS NORTHERN
WYOMING ARE ALREADY SNOWING. EXPECT THIS TREND TO CONTINUE AS THE
FRONT CONTINUES TO TRECK SOUTH THROUGH THE OVERNIGHT HOURS.

UPDATE ISSUED AT 635 PM MST MON DEC 2 2013

WINDS HAVE DECREASED IN LOWER ELEVATIONS OF CARBON COUNTY AND THE
LARAMIE VALLEY EARLY THIS EVENING. SO HAVE CANCELLED THE HIGH WIND
WARNING FOR THESE AREAS. THE CAMP CREEK OBSERVATION NEAR MUDDY GAP WAS
GUSTING TO 70 MPH AT LAST CHECK...SO WILL LEAVE THIS PORTION GOING
THROUGH 11 PM. OTHERWISE...STRONGEST WINDS WILL BE CONFINED TO THE
USUALLY WIND PRONE AREAS AROUND ARLINGTON...BORDEAUX AND OVER THE
SOUTHERN LARAMIE RANGE THIS EVENING.

UPDATE ISSUED AT 506 PM MST MON DEC 2 2013

ALLOWED HIGH WIND WARNINGS/WIND ADVISORY FOR THE SOUTHEAST WYOMING
PLAINS AND THE WESTERN NEBRASKA PLAINS TO EXPIRE ON TIME AT 5 PM.
WILL LIKELY NEED TO CANX LOWER ELEVATIONS OF CARBON COUNTY AND
ALBANY COUNTIES AS WELL HERE SHORTLY...BUT WANT TO KEEP AN EYE ON
TRENDS OVER THE NEXT HOUR OR SO BEFORE DECIDING.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 213 PM MST MON DEC 2 2013

WINDS HAVE ALREADY STARTED TO DECREASE OUTSIDE OF WIND PRONE AREAS.
MUCH OF THE HIGH WIND WARNING AND THE WIND ADVISORY FOR THE
NEBRASKA PANHANDLE WILL BE ALLOWED TO EXPIRE AT 5 PM MST. WINDS
MAY CONTINUE IN THE WIND PRONE AREA THROUGH AT LEAST MIDNIGHT.
COLD FRONT WILL REACH NORTHERN PORTIONS OF THE FORECAST AREA
SHORTLY AFTER MIDNIGHT. CURRENTLY THE FRONT HAS REACHED SOUTHEAST
AND CENTRAL MONTANA. EXPECT FALLING TEMPERATURES THROUGH THE DAY
TOMORROW FRIGID AIR CONTINUES TO SPREAD SOUTHWARD.

SNOW IS EXPECTED TO DEVELOP NEAR THE LEADING EDGE OF THE COLD
FRONT IN NORTHERN CONVERSE COUNTY TONIGHT. UPPER LEVEL ENERGY
ALONG WITH THE LOW LEVEL FORCING AND STEEP LAPSE RATES SHOULD
PRODUCE AT LEAST SOME LIGHT SNOW ACCUMULATION OVER CONVERSE
COUNTY AND INTO THE NORTHERN LARAMIE RANGE TONIGHT...BUT AS THE
FRONT PUSHES SOUTH THE UPPER DYNAMIC WILL BECOME LESS FAVORABLE
AS ENERGY FROM THE PACIFIC STORM SYSTEM LIFTS NORTH. THEREFORE NOT
EXPECTING MUCH IN THE WAY OF SNOW ALONG THE ARCTIC FRONT AS IT
REACHES SOUTHERN FORECAST AREA. ALSO SHOULD SEE A BREAK IN THE
SNOW OVER CONVERSE COUNTY STARTING LATE TUESDAY MORN INTO TUESDAY
EVENING. DID ISSUE A WINTER WEATHER ADVISORY FOR CONVERSE COUNTY
AND INTO THE NORTHERN LARAMIE RANGE BUT DO EXPECT A 6 TO 12 HOUR
BREAK IN THE SNOW...GIVEN SUBSIDENCE BETWEEN THE TWO PIECES OF
SPLIT UPPER LEVEL ENERGY

THE SOUTHERN PORTIONS OF THE SPLIT WILL BE THE MAIN INFLUENCE ON
SNOW AMOUNTS ACROSS THE AREA TUESDAY AND WEDNESDAY. THE MAIN UPPER
LEVEL FORCING FROM PVA AND JET DYNAMICS WILL OCCUR TUESDAY NIGHT
THROUGH WEDNESDAY MORNING. THIS IS WHEN THE BULK OF THE SNOW WILL
OCCUR. WITH UPSLOPE WESTERLY FLOW...SNOW WILL OCCUR ON AN OFF IN THE
SNOWY AND SIERRA MADRES RANGES TONIGHT WITH PERSISTENT LIGHT TO
MODERATE SNOW TUESDAY THROUGH WEDNESDAY. STARTED THE WINTER STORM
WARNING EFFECTIVE NOW FOR THOSE AREAS AND EXPECTING 12 TO 24
INCHES OF SNOW THROUGH WEDNESDAY AFTERNOON.

INTO LOWER ELEVATIONS IT IS A BIT MORE TRICKY. MODELS DO INDICATE
A GOOD DEAL OF LOWER TO MID LEVEL INSTABILITY FOR FAR SOUTHERN
PORTIONS OF THE FORECAST AREA TUESDAY...INCLUDING ALONG MUCH OF
INTERSTATE 80. MOISTURE IS A BIT LIMITED BUT WITH INCREASING
FRONTOGENESIS COULD SEE SOME BANDED SNOW SET IN EARLIER IN THE
DAY...BEFORE THE MAIN UPPER FORCING MOVES IN. A WINTER STORM WATCH
IS IN EFFECT FOR THIS AREA STARTING AT NOON TUESDAY...BUT SNOW
COULD DEVELOP ANYWHERE FROM TUESDAY MORNING TO TUESDAY EVENING
DEPENDING ON LOCATION AND INSTABILITY. FOR SNOW AMOUNTS WENT
CLOSER TO THE GFS WHICH IS BASICALLY MIDDLE OF THE ROAD WHEN
COMPARED TO THE MUCH WETTER ECMWF AND DRIER NAM. CONFIDENCE IN
AMOUNTS IS LOW AT THIS TIME BUT VERY CONFIDENT LOCATIONS IN THE
WATCH AREA WILL SEE AT LEAST SOME SNOW. SNOW RATIOS ALSO LEND TO
THE UNCERTAINTY. BY TUESDAY NIGHT THE SNOW FORMATION ZONE WILL BE
QUITE ELEVATED...LIKELY IN THE 600 TO 500 MB WARM ADVECTION ZONE
WHERE TEMPERATURES WILL BE 15 TO 25 DEGREES BELOW ZERO. THIS
MOSTLY LIKELY WOULD MEAN LOWER SNOW RATIOS WITH THE FAVORED ICE
CRYSTAL TYPE BEING NEEDLES AND PLATES.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 310 PM MST MON DEC 2 2013

NO SIGNIFICANT CHANGES TO THE PREVIOUS EXTENDED FORECAST WITH THE
MAIN CHANGES TO TEMPERATURES. WITH SNOW ACCUMULATION AND A SNOW
PACK LOOKING MORE LIKELY ACROSS THE AREA...LOWERED TEMPERATURES
EVEN FURTHER INTO THIS WEEKEND. THE MORE SIGNIFICANT SNOWFALL
APPEARS TO BE OVER SOUTHEAST WYOMING...SO MAINLY LOWERED
TEMPERATURES IN THESE AREAS THROUGH THE WEEKEND.

A LONG DURATION OF BITTER COLD TEMPERATURES ARE EXPECTED ACROSS
THE WHOLE FORECAST AREA THROUGH THE PERIOD AS A LARGE ARCTIC
AIRMASS SETTLES OVER THE WESTERN UNITED STATES AND NORTHERN HALF
OF THE EASTERN UNITED STATES. THE UPPER LEVEL TROUGH AND SLOW
MOVING DISTURBANCE ALOFT WILL BEGIN TO MOVE EASTWARD AND WEAKEN
WEDNESDAY NIGHT WITH ACCUMULATING SNOWFALL FINALLY COMING TO AN
END AROUND MIDNIGHT OR EARLY THURSDAY MORNING. TEMPERATURES WILL
RESPOND TO THE SNOW PACK AND PARTIALLY CLEARING SKIES...WITH LOWS
WELL BELOW ZERO ACROSS THE AREA. IN FACT...LOWERED MIN
TEMPERATURES BETWEEN 25 BELOW TO 15 BELOW ACROSS MOST OF SOUTHEAST
WYOMING AND BETWEEN 15 BELOW TO 5 BELOW ACROSS WESTERN NEBRASKA.
GIVEN RECENT MODEL TRENDS...THESE TEMPERATURES MAY BE A BIT TOO
HIGH IF ANYTHING. EVEN WITH WINDS BETWEEN 5 TO 10
KNOTS...DANGEROUS WIND CHILL VALUES BETWEEN 45 BELOW TO 30 BELOW
ARE POSSIBLE. HIGHS ON THURSDAY WILL LIKELY BE A LITTLE COLDER
COMPARED TO WEDNESDAY...MAINLY IN THE SINGLE DIGITS ABOVE AND
BELOW ZERO ACROSS SOUTHEAST WYOMING. MIGHT SEE A LITTLE MORE SUN
EARLY THURSDAY BEFORE THE NEXT UPPER LEVEL SHORTWAVE AND SECOND
SHOT OF ARCTIC AIR MOVES ACROSS THE ROCKYS.

CONDITIONS WILL NOT CHANGE SIGNIFICANTLY INTO THE WEEKEND. WIND
CHILLS WILL REMAIN BETWEEN 40 BELOW TO TO 20 BELOW ZERO AT NIGHT
WITH WIND CHILL VALUES BETWEEN 15 BELOW TO AROUND ZERO DURING THE
DAY. INCREASED TEMPERATURES A FEW DEGREES EACH DAY...BUT NOT VERY
CONFIDENT MOST OF SOUTHEAST WYOMING WILL WARM INTO THE TEENS AT
ALL THROUGH THE WEEKEND. MODELS IN BETTER AGREEMENT FOR
SATURDAY...SHOWING ANOTHER UPPER LEVEL TROUGH PUSHING ACROSS THE
AREA. STILL SOME MINOR TIMING DIFFERENCES...BUT THE GFS AND ECMWF
SHOW SOME LIGHT SNOW ACROSS THE AREA WITH ADDITIONAL ACCUMULATIONS
POSSIBLE. AFTER THE TROUGH QUICKLY MOVES EASTWARD...A PERIOD OF
ZONAL FLOW IS EXPECTED WHICH MAY RESULT IN INCREASING TEMPERATURES
ACROSS THE AREA. HOWEVER...WITH 700MB TEMPERATURES BETWEEN -8 TO
-15 AND A SNOW PACK ACROSS THE AREA...HIGHS WILL STRUGGLE TO REACH
THE LOW 20S ON MONDAY. IN ADDITION...MODELS SHOW ANOTHER STRONG
ARCTIC FRONT MOVING SOUTHWARD ALONG THE FRONT RANGE...WITH
TEMPERATURES POSSIBLY DROPPING BACK INTO THE SINGLE DIGITS EARLY
THROUGH THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY EVENING)
ISSUED AT 1045 PM MST MON DEC 2 2013

THIS PERIOD WILL FEATURE DETERIORATING AVIATION CONDITIONS AS A
POTENT ARCTIC AIR MASS PLOWS THROUGH THE REGION. AS OF 06Z...FRONT
WAS GENERALLY LOCATED ACROSS CENTRAL WYOMING PUSHING SOUTH. -SN
AND MVFR/IFR CIGS HAVE BEEN REPORTED IN THE POST-FRONTAL AIR MASS
ACROSS MUCH OF THE NORTHERN PORTIONS OF THE STATE. -SN WILL SPREAD
FIRST INTO SE WYOMING TERMINALS THIS MORNING AND THEN INTO THE
WESTERN NEBRASKA PANHANDLE DURING THE AFTERNOON HOURS. MOUNTAINS
WILL BE OBSCURED OVER THE NEXT 24 HOURS AS WELL...WHILE THIS
SYSTEM TRACKS ACROSS THE AREA.

&&

.FIRE WEATHER...
ISSUED AT 431 AM MST MON DEC 2 2013

MILD TEMPERATURES AND STRONG WINDS WILL AFFECT THE CWA TODAY ALONG
WITH PERIODS OF SNOW OVER THE SNOWY AND SIERRA MADRE RANGES.
MINIMUM RELATIVE HUMIDITY VALUES WILL BE THE LOWEST TO THE EAST
OF THE LARAMIE RANGE TODAY AND WILL BE BETWEEN 25 AND 35 PERCENT.
THEN COLD TEMPERATURES WILL BE OVER THE REGION TUESDAY THROUGH THE
WEEKEND BEHIND A COLD FRONT WHICH MOVES ACROSS THE CWA TONIGHT.
PERIODS OF SNOW WILL ALSO AFFECT THE REGION TUESDAY THROUGH
THURSDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
     AFTERNOON FOR WYZ104>106-109>111-113-115>118.

     WINTER WEATHER ADVISORY UNTIL 6 PM MST WEDNESDAY FOR WYZ101-103.

     WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR WYZ112-114.

NE...NONE.
&&

$$

UPDATE...HAHN
SHORT TERM...LIEBL
LONG TERM...TJT
AVIATION...HAHN
FIRE WEATHER...LIEBL