Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 151821
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1221 PM MDT WED APR 15 2015

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 419 AM MDT WED APR 15 2015

VERY ACTIVE SHORT TERM WITH THE POTENTIAL FOR SIGNIFICANT PRECIP
AMOUNTS. UPPER TROUGH AXIS IS CURRENTLY OVER UTAH AND IS BEGINNING
TO CLOSE OFF OVER NORTHERN UTAH. THE MODELS ARE IN GOOD AGREEMENT
AT SHOWING THE CLOSED LOW MOVING TO NEAR THE FOUR CORNERS AREA BY
THURSDAY MORNING. UPPER LEVEL DIFFLUENCE AND LARGE SCALE ASCENT
WILL INCREASE THIS AFTN AND EVENING...ESPECIALLY STRETCHING FROM
CENTRAL CARBON COUNTY INTO THE NORTHERN NEBRASKA PANHANDLE. TEMPS
BEHIND THE FRONT WILL BE COLD ENOUGH FOR SNOW AT ELEVATIONS ABOVE
5000-5500 FT. WITH THE HIGH SUN ANGLE AND RECENT STRETCH OF WARM
TEMPS...THINKING IS THAT SNOW WILL HAVE DIFFICULTY ACCUMULATING ON
ROADS THROUGH EARLY THIS EVENING. ISSUED A WINTER WEATHER ADVISORY
FOR PORTIONS OF CARBON COUNTY INTO THE SHIRLEY BASIN STARTING AT
19Z...THEN OVER THE NORTHERN LARAMIE RANGE AND LOWER ELEVATIONS OF
CONVERSE COUNTY STARTING AT 00Z. QPF AMOUNTS THROUGH THURS MORNING
ARE GENERALLY LOWER STRETCHING ALONG INTERSTATE 80 FROM LARAMIE
TO CHEYENNE...SO CONFIDENCE WAS NOT HIGH ENOUGH TO ISSUE ANY
WINTER HIGHLIGHTS AT THIS TIME. WITH SFC WET BULB TEMPS TONIGHT
JUST ABOVE FREEZING (33-40F) FROM NIOBRARA COUNTY INTO THE
NORTHERN NEBRASKA PANHANDLE...PRECIP WILL LIKELY FALL AS A MIX OF
RAIN/SNOW OR ENTIRELY AS COLD RAIN. MOST OF THE MODELS (WITH THE
EXCEPTION OF THE GFS) INDICATE PRECIP TAPERING OFF BY LATE THURS
MORNING.

PROBABLY THE BIGGEST CHANGE IN THE MODELS OVER THE PAST FEW RUNS
IS SEEN BY LATE THURS NIGHT INTO FRI. THERE IS SURPRISINGLY GOOD
AGREEMENT BETWEEN THE MODELS IN SHOWING WIDESPREAD HIGH QPF
AMOUNTS OVER THE SOUTHERN HALF OF THE CWA FROM AROUND 06Z FRI
THROUGH 00Z SAT. THE GFS AND ECMWF ARE BOTH INDICATING 0.75-2.00
INCHES OVER THIS PERIOD FROM LARAMIE INTO THE SOUTHERN PANHANDLE.
THE BIG QUESTION WILL BE WHAT PRECIP TYPE WILL OCCUR. SOUNDINGS AT
CHEYENNE SHOW SFC TEMPS JUST ABOVE FREEZING (35-38F) AND 700MB
TEMPS ARE -2C TO -4C OVER SOUTHEAST WY. THUS...THE BEST CHANCE OF
SIGNIFICANT SNOW COULD BE ACROSS THE SOUTH LARAMIE RANG AND SNOWY
RANGE...GENERALLY ABOVE 7500 FT. WOULD LIKE TO SEE AT LEAST ONE
MORE SET OF MODEL RUNS BEFORE COMPLETELY COMMITTING INTO THE IDEA
OF SIGNIFICANT QPF...BUT DID INCREASE POPS TO AROUND 50 PERCENT.
THIS IS DEFINITELY SOMETHING THAT FUTURE SHIFTS WILL HAVE TO
CONSIDER...THE POSSIBILITY OF WINTER HIGHLIGHTS STARTING THURS
NIGHT ALONG INTERSTATE 80 IN SOUTHEAST WY.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 419 AM MDT WED APR 15 2015

A COOL AND SHOWERY PERIOD EXPECTED THIS WEEKEND AND EARLY NEXT WEEK.
THE UPPER-LOW THAT WILL BRING WIDESPREAD PRECIP TO THE AREA FOR THE
LATTER HALF OF THE WEEK WILL FILL AS IT PHASES WITH THE NRN STREAM
THIS WEEKEND. BEFORE IT DOES SO...MEDIUM RANGE GUIDANCE CONTINUES TO
SUGGEST A FAIRLY HEALTHY SWATH OF PRECIPITATION ONGOING NORTH OF THE
UPPER LOW FRIDAY NIGHT. H7 TEMPERATURE PROGS ARE AROUND -2C...WHICH
WOULD KEEP THE PRECIP RAIN FOR MOST POPULOUS LOWER ELEVATIONS
EVENING FRIDAY NT. MAY MIX WITH SNOW ABOVE AROUND 8 KFT. THE UPPER
LOW BEGINS TO PHASE WITH NRN STREAM SHORTWAVE ENERGY ON SATURDAY
TAKING IT TOWARDS THE CENTRAL PLAINS. THE NRN STREAM SHORTWAVE
WILL DRAG A FRONT NORTH TO SOUTH ON SATURDAY RESULTING IN THE COOL
AND SHOWER ACTIVITY PERSISTING PERHAPS EVEN INTO SATURDAY NIGHT.
BY SUNDAY THE CWFA WILL BE ENTRENCHED IN NW FLOW...A PATTERN THAT
WILL PERSIST THRU THE FIRST HALF OF NEXT WEEK AS WELL. PRECIP
CHANCES WILL DECREASE SUNDAY AND SUNDAY NT...THOUGH KEPT LIGHT
SHOWER CHANCES CONTINUING. WOULD NOT BE SURPRISED IF THESE NEED TO
BE REMOVED WITH TIME. DRY NORTHWEST FLOW WILL PREVAIL INTO EARLY
NEXT WEEK. PERSISTENT NORTHWEST FLOW WILL HOLD HIGH TEMPS
GENERALLY IN THE 50S AND LOW 60S THRU THE PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1210 PM MDT WED APR 15 2015

RAIN AND SNOW WILL BECOME MORE WIDESPREAD TODAY AND TONIGHT AS AN
AREA OF LOW PRESSURE REMAINS NEARLY STATIONARY OVER THE 4 CORNERS
REGION. SNOW WILL MOST LIKELY OCCUR ALONG AND WEST OF THE LARAMIE
RANGE WHERE TEMPERATURES WILL BE COOLER THAN FARTHER EAST. PERIODS
OF MVFR TO IFR CIGS/VSBYS WILL OCCUR FOR KRWL/KLAR THROUGH THE
DAY. RAIN IS EXPECTED INITIALLY AT KCYS WITH A CHANGEOVER TO SNOW
LATE TONIGHT...AT WHICH POINT IFR CONDITIONS WILL BE POSSIBLE. A
FEW RUMBLES OF THUNDER CANNOT BE RULED OUT ACROSS MUCH OF THE AREA
THIS AFTERNOON AND EVENING. LOW CIGS ARE EXPECTED TO DEVELOP OVER
ALL TERMINALS BY LATE TONIGHT WITH IFR OR LOW MVFR CIGS
PREVAILING.

&&

.FIRE WEATHER...
ISSUED AT 419 AM MDT WED APR 15 2015

NO FIRE WEATHER CONCERNS OVER THE NEXT FEW DAYS.  A TRANSITION TO A
MUCH COOLER AND WETTER PATTERN WILL TAKE PLACE TODAY.  WIDESPREAD
PRECIPITATION WILL LIKELY OCCUR THIS AFTERNOON THROUGH FRIDAY
ASSOCIATED WITH A SLOW MOVING STORM SYSTEM MOVING ACROSS COLORADO.
MINIMUM RELATIVE HUMIDITY VALUES WILL GENERALLY BE ABOVE 40-50
PERCENT THROUGH FRIDAY WITH BELOW NORMAL TEMPERATURES.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL 9 AM MDT THURSDAY FOR WYZ104-105-
     109-110.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 9 AM MDT
     THURSDAY FOR WYZ101-103-106.

NE...NONE.
&&

$$

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


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