Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 270645
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1245 AM MDT MON APR 27 2015

.UPDATE...
ISSUED AT 1237 AM MDT MON APR 27 2015

UPDATED FORECAST TONIGHT TO LOWER SNOWLEVELS AS CHEYENNE HAS
ALREADY CHANGED TO SNOW...WHICH WAS NOT EXPECTED UNTIL A BIT
LATER INTO EARLY MONDAY MORNING. SNOWING HEAVILY AROUND CHEYENNE
WITH ONE HALF MILE VISIBILITY AND ONE INCH OF SNOW ON THE GROUND.
WILL NEED TO CLOSELY MONITOR SNOWFALL RATES SINCE CURRENT RADAR
LOOP SHOWS THE BAND OF PRECIPITATION EXTENDING SOUTH AND TRAINING
OVER THE SAME AREA JUST EAST OF THE LARAMIE RANGE. FOR
NOW...EXPECT AN INCH OR TWO OF SNOW...MAINLY ON THE GRASSY
SURFACES UNTIL DAWN. HOWEVER...IF THIS BAND TRAINS OVER THE SAME
AREA AROUND CHEYENNE FOR THE NEXT FEW HOURS...MAY NEED TO ADJUST
ACCUMULATIONS AND EXTEND THE WINTER WEATHER ADVISORY FURTHER EAST
THIS MORNING.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 410 PM MDT SUN APR 26 2015

CONVECTION HAS OVERSPREAD MUCH OF CARBON COUNTY AND THE CHEYENNE
RIDGE THIS AFTERNOON AS THE SHORTWAVE MOVES UP FROM COLORADO.
THUNDERSTORMS ARE MOST PROLIFIC OUT OVER SOUTHERN CARBON COUNTY AND
ARE QUITE THE LIGHTNING PRODUCERS. TEMPERATURES ARE HOLDING IN THE
UPPER 30S TO LOW 40S IN THE LOWER ELEVATIONS IN THIS AREA...WITH
LOW TO MID 30S IN THE MOUNTAINS AS STORMS MOVE OVERHEAD SO THINK
THAT SNOW LEVELS MAY BE A BIT HIGHER THAN 8000 FEET OVERALL. THE
STRENGTHENING INVERTED SFC TROUGH IS KEEPING THE COLD FRONT AT BAY
WHILE ALOFT...WATER VAPOR IMAGERY DEPICTS A SORT OF ZONAL
SHORTWAVE RIDGE OVERHEAD. IT WOULD APPEAR THAT BOTH FEATURES ARE
KEEPING THE SIGNIFICANTLY COLDER TEMPS FROM INVADING THE FORECAST
AREA FOR NOW. STILL EXPECT THE COLD FRONT TO DROP SOUTH LATE
TONIGHT THROUGH MONDAY MORNING WHILE THE UPPER LEVEL DEFORMATION
ZONE MOVES OVERHEAD...WHICH WILL BRING IN COLDER AIR AND MAINTAIN
PRECIP CHANCES ACROSS THE FORECAST AREA THROUGH TONIGHT ESPECIALLY
ALONGTHE LARAMIE RANGE AND WYO PLAINS. WILL SEE SNOW IN THE
HIGHER ELEVATIONS ABOVE 7500 FEET THIS EVENING DROPPING TO 6500
FEET OVERNIGHT...AND SHOULD MIX DOWN EVEN LOWER AS THE COLD FRONT
MOVES NORTH TO SOUTH OVERNIGHT. WILL LEAVE THE WINTER WEATHER
ADVISORY FOR NOW AS THERE IS PLENTY OF TIME FOR CONVECTION AND
DEFORMATION BAND TO ACCUMULATE SNOW IN THE SOUTHERN LARAMIE AND
SNOWY RANGES THROUGH TONIGHT. WITH THE COMBINATION DEFORMATION
BAND AND ALSO SOME MERIDIONAL JET ENERGY SNEAKING IN FROM THE WEST
OVERNIGHT...COULD ALSO SEE UP TO 5 INCHES IN THE SIERRA MADRE AND
NORTHERN LARAMIE RANGE MOUNTAINS TONIGHT...WITH AN INCH OR LESS OF
ACCUMULATION POSSIBLE IN THE LOWER ELEVATIONS OF S/E WYO WITH THE
COLD FRONT BY MONDAY MORNING. LIKELY TO SEE FOG OVERSPREAD THE
PLAINS IN THIS PATTERN AGAIN AS WELL...SO WILL KEEP MENTION OF
WIDESPREAD AREAS OF FOG IN THE FORECAST THROUGH MONDAY MORNING.

FOR MONDAY...THE UPPER JET WILL WEAKEN AS IT SHIFTS NORTH WITH THE
MIDLEVEL TROUGH MOVING OVERHEAD. WILL SEE SHOWERS CONTINUE ON AND
OFF THROUGH THE DAY WITH THE FAVORED LOCATIONS ALONG NORTHEAST
FACING SLOPES OF TERRAIN FEATURES. NOT LOOKING AT SIGNIFICANT CAA
BEHIND THE COLD FRONT OVERNIGHT SO TEMPS SHOULD MODERATE WITH
DAYTIME HEATING ENOUGH TO KEEP SNOW CONFINED TO THE MOUNTAINS. IT
IS NOT OUT OF THE QUESTION TO SEE SNOW MIX WITH RAIN AT TIMES
THOUGH EVEN ACROSS THE PLAINS AS 700MB TEMPS WILL BE AROUND MINUS
4C THROUGH THE DAY.

CONDITIONS WILL DRY OUT MONDAY NIGHT THROUGH TUESDAY AS THE UPPER
LEVEL RIDGE MOVES IN FROM THE WEST IN THE WAKE OF THE DEPARTING
UPPER LOW. HIGHS SHOULD RETURN TO THE 50S/60S BY TUESDAY.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 PM MDT SUN APR 26 2015

UPPER RIDGE BUILDING INTO THE AREA TUESDAY NIGHT WITH DRIER
CONDITIONS CONTINUING. LOOKS LIKE DRY WEATHER SHOULD STAY WITH US
THROUGH THURSDAY BEFORE ANOTHER SHORTWAVE MOVES INTO THE AREA FROM
THE NORTHWEST. PRETTY WARM TEMPERATURES EXPECTED AS 700MB
TEMPERATURES CLIMB TO AROUND +6C THURSDAY AFTERNOON.

NEXT CHANCE FOR PRECIP LOOKS TO BE THURSDAY NIGHT INTO FRIDAY AS
AN UPPER SHORTWAVE AND ASSOCIATED COLD FRONT MOVES INTO THE AREA.
BOTH THE GFS AND ECMWF BRING THE FRONT INTO THE AREA AROUND 06Z
FRIDAY (THURSDAY NIGHT) WITH SHOWERS DEVELOPING OVER THE SNOWY AND
SIERRA MADRE RANGES.

FRONTAL BOUNDARY LOOKS TO STALL NEAR THE WYOMING/COLORADO BORDER
FRIDAY AND PERSISTS INTO THE WEEKEND. BOTH THE GFS AND ECMWF
PAINTING FAIRLY WIDESPREAD QPF ALONG THE NORTH SIDE OF THIS FRONT
OVER SOUTHERN WYOMING SATURDAY INTO SUNDAY. FREEZING LINE WELL
NORTH ACROSS NORTHERN WYOMING...SO DO THINK MOST OF THIS
PRECIPITATION WILL FALL AS RAIN NEXT WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1131 PM MDT SUN APR 26 2015

ABUNDANT AVAILABLE MOISTURE ALONG WITH PERSISTENT EASTERLY UPSLOPE
FLOW WILL CONTINUE TO PRODUCE POOR AVIATION CONDITIONS AT MOST
TERMINALS THRU AT LEAST THE MORNING HOURS. WIDESPREAD LIFR/IFR
CONDITIONS ANTICIPATED AT SOUTHEAST WYOMING TERMINALS THRU 18Z.
STRATUS SHOULD LIFT SOME BY MIDDAY...BUT DID ADD SOME ADDITIONAL
-SHRA AFTER 18Z. CONDITIONS WILL BE SLIGHTLY BETTER AT WRN
NEBRASKA SITES WHERE SOME MVFR CONDITIONS CAN BE EXPECTED. THE ONE
EXCEPTION MAY BE KCDR...WHERE SOME LOWER CONDITIONS MAY SNEAK IN
AROUND DAYBREAK. EXPECT LITTLE IF ANY CHANCE FOR SHOWER
DEVELOPMENT AT THESE SITES ON MONDAY...SO HAVE LIFTED THEM BACK TO
VFR BETWEEN 16-18Z. MOUNTAINS WILL BE OBSCURED THROUGH MUCH OF
MONDAY.


&&

.FIRE WEATHER...
ISSUED AT 410 PM MDT SUN APR 26 2015

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THIS WEEK AS A
PERIOD OF UNSETTLED WEATHER WILL CONTINUE ACROSS SOUTHEAST WYOMING
AND WESTERN NEBRASKA. PERIODS OF RAIN SHOWERS AND HIGH ELEVATION
SNOW ARE EXPECTED INTO MONDAY. MUCH DRIER CONDITIONS WILL RETURN
BY MIDWEEK WITH DAYTIME RELATIVE HUMIDITIES TRENDING LOWER TOWARDS
THE 20 PERCENT RANGE ON WEDNESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL 6 AM MDT EARLY THIS MORNING FOR
     WYZ114-116.

NE...NONE.
&&

$$

UPDATE...TJT
SHORT TERM...RJM
LONG TERM...GCC
AVIATION...CAH
FIRE WEATHER...RJM


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