Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 161805
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1205 PM MDT THU APR 16 2015

.SHORT TERM...(TODAY THROUGH FRIDAY NIGHT)
ISSUED AT 435 AM MDT THU APR 16 2015

SIGNIFICANT STORM STILL EXPECTED TO IMPACT THE HIGHER ELEVATIONS
FROM LATE THIS AFTERNOON THROUGH MIDDAY FRIDAY. WATER VAPOR
IMAGERY SHOWS THE CLOSED UPPER LOW SPINNING JUST WEST OF THE FOUR
CORNERS REGION. WE ARE GETTING A BREAK IN THE PRECIP...HOWEVER
THIS WILL LIKELY BE SHORT LIVED (ONLY THROUGH THIS MORNING) AS
CLOUD TOPS ARE COOLING IN COLORADO. THE MODELS CONTINUE TO
INDICATE EXCELLENT LARGE SCALE LIFT DEVELOPING IN AREAS ALONG THE
COLORADO BORDER BY LATE THIS AFTN. UPWARD VERTICAL MOTION IS
MAXIMIZED FROM 21Z THIS AFTN THROUGH 12Z FRI IN THE SOUTHERN HALF
OF THE CWA. THIS IS DUE TO EXCELLENT UPPER LEVEL DIFFLUENCE AND
ISENTROPIC LIFT. WHILE WIDESPREAD SUBSTANTIAL QPF AMOUNTS ARE
VERY LIKELY...THE TRICKIER PART OF THIS FCST INVOLVED THE SNOW
LEVEL AND ASSOCIATED SNOW ACCUMULATIONS.

THE 00Z GUIDANCE CAME IN A BIT WARMER THAN YESTERDAY WITH RESPECT
TO SFC TEMPS FROM LATE THIS AFTN THROUGH FRIDAY MORNING. WARM AIR
ADVECTION IS OCCURRING AS 700MB TEMPS AT CHEYENNE RISE FROM -4C
THIS MORNING TO -1C BY FRI MORNING. THE CYS SOUNDING FROM BOTH THE
NAM AND GFS SHOW SFC TEMPS OF 2-3C WITH COMPLETE SATURATION
THROUGH TONIGHT. THUS...DESPITE THE STRONG LLVL LIFT...THINKING
IS THAT A MIX OF RAIN/SNOW OR ALL RAIN WILL OCCUR BETWEEN
ELEVATIONS OF 6250-5500 FT WITH THIS EVENT. DECIDED TO CANCEL THE
WINTER STORM WATCH FOR CENTRAL LARAMIE COUNTY AND EAST PLATTE
COUNTY WITH THIS REASONING...AND WILL LET DAY SHIFT SEE IF THE 12Z
GUIDANCE COMES IN ANY COOLER OR IF ANY DRIER AIR COULD CAUSE SOME
WET-BULBING. THE PRECIP WILL START OUT AS ALL SNOW AT ELEVATIONS
ABOVE 6500 FT THIS AFTN AND EARLY EVENING...WITH THE SNOW LEVEL
POSSIBLY RISING TO AROUND 7500 FT BY FRI MORNING. THE WINTER STORM
WATCH WAS UPGRADED TO A WARNING FROM JUST WEST OF CHEYENNE TO
ARLINGTON AND ALSO FOR THE SNOWY RANGE.  WHILE TRAVEL WILL BE
AFFECTED ALONG INTERSTATE 80 FROM CHEYENNE TO ARLINGTON...THE
BIGGEST IMPACTS WILL LIKELY BE OVER THE FROM BUFORD TO THE
INTERSTATE 80 SUMMIT WHERE UP TO A FOOT OF SNOW IS FCSTED.

BY FRI AFTN THE UPPER LOW WILL HAVE MOVED INTO CENTRAL COLORADO.
THE MODELS SHOW VERY GOOD LIFT AND WIDESPREAD PRECIP ACROSS THE
CWA THROUGH THE AFTN. DECIDED TO END THE WINTER STORM HIGHLIGHTS
AT 18Z FRI AS SFC TEMPS WILL LIKELY BE ABOVE FREEZING ACROSS ALL
ZONES EXPECT MAYBE THE HIGHER ELEVATIONS OF THE SNOWY RANGE. THE
BAND OF PRECIP IS PROGGED TO SHIFT NORTHWARD FROM NORTHERN CARBON
TO THE NORTHERN NEBRASKA PANHANDLE BY FRI EVENING. IT IS AT THIS
TIME THAT DRIER AIR WILL WORK INTO THE SOUTHERN HALF OF THE CWA
AND PRECIP WILL DIMINISH. WITH MOST OF THE MODELS INDICATING QPF
AMOUNTS OF 1.25-2.0 INCHES FROM THIS AFTERNOON THROUGH FRIDAY
NIGHT FOR AREAS ALONG AND EAST OF THE LARAMIE RANGE...CONFIDENCE
IS HIGH THAT THIS SYSTEM WILL BRING WELL NEEDED MOISTURE TO THE
REGION.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 435 AM MDT THU APR 16 2015

A COOL AND SHOWERY PERIOD STILL EXPECTED ACROSS THE CWFA THIS
WEEKEND AND EARLY NEXT WEEK AS NORTHWEST FLOW PREVAILS. REMNANTS
OF THE UPPER LOW THAT WILL HAVE WOBBLED AROUND COLORADO FOR THE
BETTER PART OF 3 DAYS LATE THIS WEEK...WILL CARRY LINGERING
IMPACTS ACROSS THE REGION EVEN INTO SATURDAY. 00Z MEDIUM RANGE
GUIDANCE ARE CONSISTENT IN PINWHEELING A FINAL VORT LOBE SOUTH TO
NORTH THRU THE AREA ON SATURDAY. MODELS TARGET WRN AND NRN ZONES
WITH THE BEST AXIS OF PRECIP ON SATURDAY...THOUGH COOL MID-LEVEL
TEMPS WILL BE ENOUGH TO PRODUCE THE POSSIBILITY OF SHOWERS
EVERYWHERE. FINALLY...THE UPPER-LOW WILL FULLY PHASE INTO THE NRN
STREAM BY SUNDAY. 00Z MODELS HAVE TRENDED DEEPER/STRONGER WITH
KICKER SYSTEM HOWEVER. THIS WILL RE-ENFORCE PRECIP CHANCES FOR
SUNDAY. IT LOOKS SOMEWHAT DRIER MON-TUE...THOUGH STILL CANT
COMPLETELY RULE OUT SOME LIGHT SHOWER ACTIVITY ESPECIALLY IN AND
AROUND THE HIER TERRAIN. ANOTHER WEAK SHORTWAVE MAY BRING ADDL
SHOWER CHANCES TO THE AREA WED-THU. NONE OF THESE SHOWER CHANCES
WILL AMOUNT TO MUCH THO. TEMPS WILL BE THE COOLEST THIS WEEKEND
WITH HIGHS ONLY REACHING THE UPPER 40S TO NR 50 IN AND AROUND THE
MOUNTAINS WITH 50S TO NR 60 OUT ON THE ERN PLAINS. THESE SHOULD
WARM BACK INTO THE 50S AND MID 60S MON-WED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1156 AM MDT THU APR 16 2015

IFR/LIFR CIGS AND VSBYS ARE ALREADY OCCURRING WITH WIDESPREAD
MODERATE TO HEAVY SNOW ALONG AND SOUTH OF I80 IN WY. THIS WILL
CONTINUE THROUGH THE DAY WITH SNOW POSSIBLY MIXING WITH RAIN AT
ELEVATIONS BELOW 7000 FEET BY LATE AFTN. KLAR AND KRWL WILL SEE
ALL SNOW THROUGH THE TAF PERIOD...WITH BETTER CHANCES FOR MIXED
PRECIPITATION AT TIMES FOR KCYS. RAIN IS EXPECTED FOR PANHANDLE
TERMINALS. A FEW LIGHTNING STRIKES COULD OCCUR OVER SOUTHEAST WY
AND THE SOUTHERN NE PANHANDLE THIS AFTN AND EVE. RAIN/SNOW RATES
SHOULD DIMINISH OVERNIGHT...BUT ANOTHER ROUND OF HEAVY PRECIP IS
LIKELY ALONG THE I80 CORRIDOR AFTER 09Z FRI. WIDESPREAD IFR
CONDITIONS SHOULD PREVAIL.

&&

.FIRE WEATHER...
ISSUED AT 347 AM MDT THU APR 16 2015

NO FIRE WEATHER CONCERNS THROUGH THE WEEKEND. A COOL AND VERY WET
PATTERN WILL BE IN PLACE THROUGH FRIDAY. WIDESPREAD RAIN ACROSS
THE LOWER ELEVATIONS AND SNOW IN THE MOUNTAINS WILL OCCUR.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL NOON MDT FRIDAY FOR WYZ114>117.

     WINTER WEATHER ADVISORY UNTIL NOON MDT FRIDAY FOR WYZ112-118.

     WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO NOON MDT
     FRIDAY FOR WYZ103-105-106-110.

NE...NONE.
&&

$$

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



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