Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 012143
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
243 PM MST SUN FEB 1 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 243 PM MST SUN FEB 1 2015

PROGRESSIVE NORTHWEST FLOW EMBEDDED WITH A SERIES OF WEAK
SHORTWAVES AND ASSOCIATED JET STREAKS WILL DOMINATE THE FIRST HALF
OF THE WEEK. IMPACTS FROM THIS WILL BE A RETURN TO WINDY
CONDITIONS ACROSS THE SE WY WIND CORRIDOR ALONG WITH A LONG
DURATION MAINLY LIGHT SNOW EVENT FOR THE SNOWY AND SIERRA MADRE
RANGES. LETS LOOK AT A RETURN TO HIGH WINDS FOR PORTIONS OF SE WY
FIRST. TWO DISTINCT HIGH WIND EVENTS SETTING UP...THE FIRST MORE
MARGINAL EVENT WILL BE TONIGHT. LLVL KCAG-KCPR GRADIENTS PEAK
50-60 METERS 03-18Z. WIND CORRIDOR CROSS-SECTIONS DEPICTS
DESCENDING STABLE LAYER LATE TONIGHT AS WELL AND WITH 50 KNOT
WINDS BENEATH IT...CONFIDENCE IS GROWING THAT LOCATIONS AT LEAST
IN THE ARLINGTON AREA WILL REACH CRITERIA. SO HAVE OPTED TO HOIST
A HIGH WIND WARNING 04-19Z. WOULD LIKE TO SEE H85 GRADIENTS A BIT
HIGHER TO INCLUDE SW PLATTE COUNTY...SO WILL HOLD OFF FOR NOW.
GRADIENTS STEP BACK MONDAY AFTERNOON AND EARLY EVENING AS PBL
MIXING EFFECTIVELY BROADEN MOMENTUM TRANSFER. THE SECOND HIGH
WIND EVENT TAKES SHAPE LATE MONDAY NT THRU TUESDAY MORNING. LLVL
KCAG-KCPR GRADIENTS AGAIN INCREASE TO CRITICAL THRESHOLDS...THOUGH
SLIGHTLY LESS THAN 00Z RUNS. THESE STRONG GRADIENTS COMBINE WITH
AN APPROACHING ANTICYCLONIC JET STREAK TO SFC THESE STRONGER
WINDS. THE INHERITED HIGH WIND WATCH IS ON TRACK MONDAY
NT/TUESDAY. AREAS AWAY FROM THE WIND CORRIDOR WILL TURN BREEZY AS
WELL...WHICH WILL RESULT IN EFFECTIVE ADIABATIC DOWNSLOPE WARMING
OVR THE ERN PLAINS MON-TUE. HIGH TEMPS WILL WARM INTO UPPER 40S
AND LOW 50S EACH DAY AS A RESULT.

THE OTHER CONCERN IS THE LIKELIHOOD OF A LONG DURATION LIGHT SNOW
EVENT FOR THE SNOWY/SIERRA MADRE RANGES. FAVORABLE OROGRAPHIC FLOW
H8/H7 LAYER OF AROUND 30 KNOTS COMBINED WITH A SERIES OF
SHORTWAVES EACH EMBEDDED WITH MID-LEVEL MOISTURE ADVECTION WILL
KEEP THE SNOW MACHINE GOING IN THE MOUNTAINS. SNOWFALL RATES DO
NOT LOOK TO BE HIGH ENOUGH TO WARRANT A HIGHLIGHT. HOWEVER...WITH
1-2 INCHES EXPECTED DURING EACH 6-HOUR PERIOD...MAY SEE OVER A
FOOT OF NEW SNOW BETWEEN TONIGHT THROUGH TUESDAY NIGHT.

THE APPROACH OF A STRONG COLD FRONT TUESDAY NT WILL BRING THE NEXT
CHANCE OF SNOW TO LOWER ELEVATIONS. MODEL TIMING DIFFERENCES
REMAIN WITH THE GFS40 THE QUICKEST DROPPING SNOW SOUTH THRU THE
AREA LATE TUESDAY NT...WHILE THE NAM IS THE SLOWEST IN KEEPING BEST
SNOW CHANCES TO WEDNESDAY. HAVE INCREASED SNOW CHANCES SLIGHTLY
SOME TUESDAY NT...THOUGH STILL THINK THE GREATEST IMPACTS WILL BE
FELT ON WEDNESDAY.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 243 PM MST SUN FEB 1 2015

WEDNESDAY STILL LOOKING RATHER COLD WITH SNOW AS A SFC HIGH DROPS
INTO THE NORTHERN PLAINS AND CREATES A FAVORABLE OVERRUNNING
PATTERN ACROSS THE CWA. GFS A BIT FASTER WITH THE SYSTEM BUT
MODELS IN OVERALL GOOD AGREEMENT. SHOULD SEE AT LEAST A FEW
INCHES OF SNOWFALL OVER MANY AREAS. SNOW WILL END FROM NORTH TO
SOUTH WEDS AFTERNOON AND EVENING AS THE SFC HIGH SETTLES FARTHER
SOUTH INTO THE PLAINS AND THE SFC UPSLOPE FLOW OVER THE CWA
DIMINISHES. SOME SNOW SHOWERS SHOULD PERSIST OVER THE HIGHER MTNS
WEDS NIGHT. RETURN FLOW THURSDAY WILL RETURN WARMER TEMPS
BEGINNING THURSDAY WITH UPPER RIDGING MOVING TOWARDS THEN ACROSS
THE REGION THURSDAY AND FRIDAY. LOOKING LIKE A MILD BUT WINDIER
PATTERN FRIDAY THROUGH THE WEEKEND AS A MORE ZONAL FLOW SETS UP
WITH A COUPLE IMPULSES MOVING ACROSS BRINGING SOME MAINLY MTN SNOW
SHOWERS AS WELL AS STEEPENING THE SFC PRESSURE GRADIENT DUE TO
ENHANCED LEE TROFFING.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 243 PM MST SUN FEB 1 2015

VFR EXPECTED THIS EVENING WITH INCREASING HIGH CLOUDS. SFC WINDS
WILL ALSO INCREASE AROUND THE SE WY MTNS THIS EVENING AS WELL.
SNOW SHOWERS SHOULD INCREASE OVER THE HIGHER SE WY MTNS LATER
TONIGHT WITH MVFR/IFR CIGS AFFECTING THE KRWL VCTY LATER TONIGHT
INTO MONDAY.

&&

.FIRE WEATHER...
ISSUED AT 243 PM MST SUN FEB 1 2015

NO FIRE WEATHER CONCERNS INTO EARLY NEXT WEEK. HIGH TEMPERATURES
WILL RETURN TO THE 40S AND 50S FOR MONDAY AND TUESDAY. MOUNTAIN
SNOW ALONG WITH BREEZY TO LOCALLY WINDY CONDITIONS WILL RETURN
LATE TONIGHT THROUGH TUESDAY AS WELL. MINIMUM RELATIVE HUMIDITIES
WILL NOT DROP BELOW 30 PERCENT DURING THIS PERIOD.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING FROM 9 PM THIS EVENING TO NOON MST MONDAY FOR
     WYZ110.

     HIGH WIND WATCH FROM MONDAY EVENING THROUGH TUESDAY AFTERNOON
     FOR WYZ106-110-116-117.

NE...NONE.

&&

$$

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


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