Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 281010
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
410 AM MDT THU APR 28 2016

.SHORT TERM...(TODAY THROUGH FRIDAY NIGHT)
ISSUED AT 350 AM MDT THU APR 28 2016

MAIN FORECAST CONCERN WILL BE THE NEXT PACIFIC WINTER STORM
FORECAST TO BEGIN IMPACTING THE REGION TODAY. RELATIVELY QUIET
WEATHER THIS MORNING WITH LOW CLOUDS AND SOME PATCHY FOG. WATER
VAPOR SATELLITE LOOP SHOWS THE STORM SYSTEM WHICH BROUGHT SOME
LIGHT RAIN AND SNOW TO WESTERN NEBRASKA YESTERDAY...FINALLY
PUSHING NORTHEAST TOWARDS THE GREAT LAKES REGION. THIS WILL ALLOW
THE NEXT STORM TO IMPACT THE REGION BY THIS AFTERNOON. SATELLITE
SHOWS A DEVELOPING AREA OF LOW PRESSURE ACROSS THE SOUTHERN GREAT
BASIN REGION. MODELS SHOW THIS UPPER LEVEL LOW AND ASSOCIATED
SURFACE LOW SLOWLY MOVING NORTHEAST INTO UTAH AND WESTERN COLORADO
TONIGHT. ALTHOUGH THE WORST IMPACTS ARE STILL 24+ HOURS
AWAY...SOME WARM AIR ADVECTION ALOFT MAY PRODUCE A BAND OF
OVERRUNNING PRECIPITATION BY THIS AFTERNOON ACROSS THE AREA. THE
WARM FRONT WILL NEVER MAKE IT THROUGH THE AREA HOWEVER...SO EXPECT
SNOW LEVELS TO REMAIN BETWEEN 5000 TO 6000 FEET. PRECIPITATION
SHOULD BE LIGHT THIS AFTERNOON WITH ONLY AN INCH OF SNOW EXPECTED
ABOVE 6000 FEET. HIGH TEMPERATURES WILL REMAIN COOL...AND
GENERALLY IN THE 30S TO NEAR 40 ACROSS SOUTHEAST WYOMING...WITH
AFTERNOON READINGS IN THE MID TO UPPER 40S ACROSS WESTERN
NEBRASKA.

PERIODS OF LIGHT SNOW ARE EXPECTED THURSDAY NIGHT BEFORE THE MAIN
EVENT BEGINS ACROSS EASTERN COLORADO. MODELS NOW SHOW THE UPPER
LEVEL LOW BARELY MOVING AT ALL THROUGH EARLY FRIDAY MORNING AS A
POTENT DISTURBANCE ROUNDS THE BASE OF THE LOW ACROSS NEW MEXICO
AND EASTERN COLORADO. MODELS ARE HINTING AT THE OVERALL LONG WAVE
TROUGH OVER THE ROCKYS BECOMING NEGATIVELY TILTED AS THE MAIN
IMPACTS FROM THE STORM BEGIN ACROSS SOUTHEAST WYOMING EARLY FRIDAY
MORNING. EVEN BY FRIDAY EVENING...THE UPPER LEVEL LOW IS ONLY OVER
CENTRAL COLORADO. THE GFS CONTINUES TO INDICATE AN IMPRESSIVE AREA
OF PRECIPITATION ACROSS THE HIGH PLAINS DURING THIS TIME WITH QPF
AMOUNTS OVER ONE INCH SOUTH OF A LINE FROM WHEATLAND TO BRIDGEPORT
NEBRASKA. THE SREF SUPPORTS THIS IDEA AS MOST OF ITS MEMBERS ARE
AGGRESSIVE EARLY FRIDAY MORNING WITH PRECIPITATION/SNOWFALL RATES.
HOWEVER...THE ECMWF IS A LITTLE FURTHER SOUTH AND SHOWS MUCH LOWER
QPF OVER THE WHOLE AREA...INCLUDING COLORADO...THROUGH FRIDAY.
ECMWF FINALLY INCREASES THE PRECIP RATES FRIDAY NIGHT ACROSS THE
HIGH PLAINS. WITH VERY GOOD UPSLOPE FLOW...THETA E ADVECTION SOUTH
OF THE NORTH PLATTE RIVER VALLEY...AND IMPRESSIVE DIFFLUENCE
ALOFT...BELIEVE THE HIGH PLAINS OF SOUTHEAST WYOMING AND WESTERN
NEBRASKA ARE IN FOR A PROLONGED PRECIP EVENT. SNOWLEVELS WILL
INITIALLY BE 4500 TO 5500 FEET BEFORE LOWERING ON SATURDAY. ANY
POTENTIAL TRAVEL IMPACTS WILL GREATLY DEPEND ON TIMING OF THE
HEAVIEST SNOW. JUST NOT CONFIDENT ENOUGH WITH THE TIMING OF THE
HEAVIEST PRECIPITATION RATES AS OF YET TO UPGRADE THE WINTER STORM
WATCH ACROSS LARAMIE COUNTY TO A WARNING OR EXTEND THE WATCH
FURTHER EAST...BUT CONFIDENCE IS INCREASING. SOME SNOW
ACCUMULATIONS ARE LOOKING INCREASING LIKELY ACROSS WESTERN
NEBRASKA AS WELL...BUT LATER IN THE FORECAST PERIOD.

FOR THE REMAINDER OF THE WINTER STORM WATCH INHERITED FROM
YESTERDAY...DECIDED TO UPGRADE THE SNOWY RANGE AND I80 SUMMIT
BETWEEN LARAMIE AND CHEYENNE TO A WARNING FOR SNOW ACCUMULATIONS
OF 10 TO 15 INCHES AND SNOW PACKED ROADS. UPSLOPE COMPONENT
SHOULD BE ENOUGH FOR SEVERAL LOCATIONS IN THESE AREAS TO SEE
WARNING CRITERIA. WITH SOUTHEAST TO EASTERLY WINDS AT THE
SURFACE...THIS IS NOT A GOOD SETUP FOR THE LARAMIE VALLEY AS
WINDS VEER INTO THE SOUTHWEST ALOFT. LARAMIE AND SURROUNDING AREAS
WILL LIKELY SEE A SNOW SHADOW EFFECT UNTIL FRIDAY NIGHT WHEN
WINDS FINALLY SHIFT INTO THE NORTH OR NORTHEAST...BUT MOST OF THE
EVENT WILL BE OVER BY THEN. THE SAME APPLIED TO THE SIERRA MADRE
RANGE WHICH DOES NOT DO AS WELL IN EASTERLY FLOW. BY LATE FRIDAY
NIGHT...MODELS SHOW THE STORM MOVING FURTHER EAST INTO FAR EASTERN
COLORADO OR EXTREME SOUTH CENTRAL NEBRASKA...BUT THEN STALLING
AGAIN. EXPECT LIGHT SNOW TO LINGER THROUGH LATE FRIDAY NIGHT AND
INTO EARLY SATURDAY MORNING...WHICH IS WHEN MOST OF WESTERN
NEBRASKA MAY CHANGE TO ALL SNOW. WILL HAVE TO MONITOR THIS AREA
FOR POTENTIAL WINTER HEADLINES.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 320 AM MDT THU APR 28 2016

COOL AND UNSETTLED WEATHER TO PERSIST OVER THE CWA SATURDAY AND
SUNDAY AS ONE UPPER LOW OVER NEBRASKA MOVES AWAY BUT YET ONE MORE
MOVES INTO THE DESERT SW SATURDAY. SNOW WILL CONTINUE TO BE LIKELY
OVER THE MUCH OF THE AREA SAT AND SATURDAY NIGHT WITH SUFFICIENTLY
LOW THICKNESS VALUES WITH RAIN AND SNOW SHOWERS TAPERING OFF ON
SUNDAY. LOOKS LIKE THE CWA WILL FINALLY SEE A DRYING PATTERN
ARRIVE MONDAY AS THE SECOND UPPER LOW OPENS AND SHEARS OUT TO THE
EAST SUNDAY NIGHT AND A FAIRLY LARGE AMPLITUDE UPPER RIDGE BUILDS
OVER MUCH OF THE WESTERN CONUS MONDAY AND TUESDAY...AND EDGES
EASTWARD OVER THE ROCKY MTN CHAIN WEDS. THIS WILL ALLOW WARMER
TEMPS TO ENSUE EARLY NEXT WEEK...NEAR SEASONAL AVERAGES TUESDAY
AND WEDS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 320 AM MDT THU APR 28 2016

AREAS OF MVFR/IFR CIGS THIS MORNING SHOULD IMPROVE SOME OVER THE
PANHANDLE THIS AFTERNOON. MVFR/IFR CIGS AND VSBYS EXPANDING OVER
THE AREA TONIGHT WITH AREAS OF RAIN AND SNOW SPREADING OVER MAINLY
FAR SE WY AND THE SRN NEB PANHANDLE THIS AFTERNOON THROUGH
TONIGHT.

&&

.FIRE WEATHER...
ISSUED AT 320 AM MDT THU APR 28 2016

NO FIRE WEATHER CONCERNS OVER THE NEXT 7 DAYS. BELOW NORMAL
TEMPERATURES AND PERIODS OF WIDESPREAD PRECIPITATION ARE
EXPECTED ACROSS SOUTHEAST WYOMING AND WESTERN NEBRASKA THROUGH
THIS WEEKEND.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 AM MDT SATURDAY
     FOR WYZ114-116.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MDT
     FRIDAY FOR WYZ112.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM MDT
     SATURDAY FOR WYZ110-115.

     WINTER STORM WATCH FROM LATE TONIGHT THROUGH LATE FRIDAY NIGHT
     FOR WYZ117>119.

NE...NONE.
&&

$$

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


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