Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 150002
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
502 PM MST SUN DEC 14 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 315 PM MST SUN DEC 14 2014

CHALLENGING FORECAST FOR TONIGHT AND MONDAY AS THIS WINTER STORM
SYSTEM IS JUST STARTING TO GET GOING OVER THE CENTRAL AND SOUTHERN
PLAINS. HOWEVER...A BIT MORE CONFIDENCE ABOUT THE FORECAST FOR
TONIGHT COMPARED TO 24 HOURS AGO WITH MODELS TRENDING TOWARDS
SIMILAR SOLUTION. FIRST...WILL START WITH THE WINTRY CONDITIONS
ALONG AND WEST OF THE LARAMIE RANGE. CURRENT KCYS RADAR LOOP HAS
SHOWN MAINLY LIGHT SNOW THROUGH MOST OF THE DAY WEST OF THE
LARAMIE RANGE. DID NOT GET THE BURST OF MODERATE SNOW DURING THE
DAY TODAY...SO ACCUMULATIONS APPEAR TO BE BETWEEN 1 TO 3 INCHES. A
FEW LOCATIONS HAVE REPORTED AROUND 6 INCHES...BUT THOSE AREAS ARE
MAINLY IN THE MOUNTAINS. EXPECT PERIODS OF LIGHT SNOW TO CONTINUE
TONIGHT NORTH OF THE I80 CORRIDOR FROM RAWLINS TO DOUGLAS.
EXTENDED THE WINTER WEATHER ADVISORY IN THESE LOCATIONS UNTIL
EARLY MONDAY MORNING FOR AN ADDITIONAL 1 TO 2 INCHES OF SNOW AND
SNOWPACKED ROADWAYS.

AS FOR THE HIGH PLAINS...CURRENTLY TRACKING A LOW PRESSURE SYSTEM
WHICH DEVELOPED OVER EXTREME SOUTHEAST COLORADO THIS MORNING AND
IS TRACKING NORTHEAST INTO KANSAS. THIS STORM TRACK IS SLIGHTLY
NORTHWEST OF WHAT MOST MODELS WERE SHOWING YESTERDAY...HENCE THE
ADJUSTMENT OF SNOW ACCUMULATIONS ACROSS THE FORECAST AREA. THE
MAIN MODEL DIFFERENCES COMPARED TO YESTERDAY ARE THE ECMWF
TRENDING SOMEWHAT LESS AGGRESSIVE WITH SNOWFALL ACROSS THE
SOUTHERN PANHANDLE...AND THE GFS AND GEM NOW HIGHLIGHTING THE
NORTHERN PANHANDLE FOR THE MOST SNOWFALL TONIGHT...MAINLY IN THE
CHADRON...ALLIANCE...TO LUSK AREA ACROSS THE PINE RIDGE. QPF
AMOUNTS NEAR A HALF INCH LIQUID ARE STILL FORECAST IN THESE AREAS
BETWEEN THIS EVENING AND 3 AM MONDAY MORNING. ALTHOUGH THE SURFACE
LOW AND JET DYNAMICS ARE EAST OF THE FORECAST AREA...THE CYCLONIC
WARM AIR CONVEYOR BELT ALOFT (TROWAL) IS THE MAIN FORCING
MECHANISM FOR THIS EVENT. ANALYSIS OF THETA E ADVECTION ALOFT
INDICATES THE BEST WRAP AROUND SNOWFALL REMAINING JUST EAST OF A
LINE FROM SIDNEY TO CHADRON NEBRASKA TONIGHT. HOWEVER...THERE IS
ENOUGH LIFT TO GENERATE LOCALLY HEAVY SNOWFALL AT TIMES AS THE
FORECAST AREA GETS BRIEFLY CLIPPED BY THIS ENHANCED LIFT THIS
EVENING. ALREADY SEEING SOME HEAVY SNOW BANDS ENTERING THE
SOUTHERN PANHANDLE THIS AFTERNOON. IN ADDITION...THERE IS SOME
ELEVATED FRONTOGENESIS ACROSS ALL OF THE HIGH PLAINS
ZONES...INCLUDING THE I25 CORRIDOR. INCREASED SNOW ACCUMULATIONS
WITH 1 TO 3 INCHES EXPECTED ACROSS FAR SOUTHEAST
WYOMING...INCLUDING CHEYENNE AND TORRINGTON. 2 TO 5 INCHES ARE
EXPECTED ACROSS NIOBRARA AND CONVERSE COUNTIES WHERE A WINTER
WEATHER ADVISORY HAS BEEN ISSUED FOR TONIGHT FOR SNOW AND BLOWING
SNOW. ACROSS THE WESTERN PANHANDLE...ACCUMULATION FORECASTS WILL
BE TRICKY SINCE HEAVY SNOW BANDS MAY TRAIN OVER THE SAME AREA
RESULTING IN LOCALLY HIGHER AMOUNTS. GENERALLY ANTICIPATE 3 TO 7
INCHES OF SNOW WITH SNOWFALL ACROSS THE NORTHERN PANHANDLE LASTING
A LITTLE LONGER INTO MONDAY. THERE IS CONCERN OF QUARTER MILE
VISIBILITIES AND GUSTY WINDS OVER 30 MPH...WHICH MAY CAUSE BLOWING
AND DRIFTING. HOWEVER...THE WORST CONDITIONS WILL NOT LAST TOO
LONG AS MODELS INDICATE THE FAVORABLE DYNAMICS QUICKLY PUSHING
NORTHWARD AFTER MIDNIGHT. INCLUDED ALL OF THE WESTERN PANHANDLE IN
THE WINTER WEATHER ADVISORY AND WORDED THE STATEMENT A LITTLE MORE
AGGRESSIVE FOR GUSTY WINDS AND LOW VISIBILITIES.

THE HEAVIEST SNOWFALL WILL COME TO AN END BY MONDAY MORNING WITH
THE MAIN HAZARDS BEING LIGHT TO MODERATE SNOW AND BLOWING SNOW
OVER THE FAR EASTERN PLAINS. KEPT THE WINTER WEATHER ADVISORY
GOING UNTIL NOON MONDAY FROM DOUGLAS WYOMING TO CHADRON NEBRASKA
AS SNOWFALL WILL LINGER ACROSS THESE LOCATIONS FOR A WHILE.
FURTHER SOUTH...SNOW WILL TAPER OFF TO FLURRIES AND END ACROSS THE
I80 CORRIDOR WITH COLD TEMPS AND BRISK WINDS MONDAY AFTERNOON.

COLD BUT PLEASANT WEATHER IS EXPECTED FOR MONDAY NIGHT AND INTO
TUESDAY OUTSIDE OF SOME MOUNTAIN SNOW SHOWERS. WILL HAVE TO ADJUST
OVERNIGHT LOWS MONDAY NIGHT AS RADIATIONAL COOLING DUE TO SNOW
PACK IS EXPECTED ACROSS PORTIONS OF THE HIGH PLAINS. FOR
NOW...INTRODUCED SOME READINGS NEAR ZERO ACROSS THE PANHANDLE AND
HIGH VALLEYS WEST OF THE LARAMIE RANGE.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 14 2014

UPPER RIDGE OVER THE CWFA TUESDAY NIGHT. PRETTY MUCH DRY WITH THE
EXCEPTION OF MAYBE THE SNOWY AND SIERRA MADRE RANGES...WHERE SNOW
SHOWERS COULD LINGER. LOOKS PRETTY COLD TUESDAY NIGHT WITH THE
COMBINATION OF CLEARING SKIES...LIGHT WINDS AND SNOWPACK. LOOKING
AT LOWS IN THE UPPER SINGLE DIGITS AND LOW TEENS ACROSS SOUTHEAST
WYOMING AND NEBRASKA PANHANDLE.

UPPER RIDGE TRANSLATES EAST FR WEDNESDAY. GOING TO STAY FAIRLY
COLD WITH 700MB TEMPERATURES REMAINING AROUND -6 TO -8C. HIGHS IN
THE 30S SHOULD BE WIDESPREAD. LOOKS LIKE WE KEEP THESE COLDER
TEMPERATURES OVER THE CWFA THROUGH THE WEEK...WITH MAINLY DRY
CONDITIONS. DO NOT SEE ANY SYSTEMS MOVING THROUGH THE AREA THROUGH
SATURDAY/SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 448 PM MST SUN DEC 14 2014

MOUNTAINS WILL REMAIN OBSCURRED TONIGHT WITH IMPROVEMENT
THROUGH DAY MONDAY. WIDESPREAD IFR TO MVFR ACROSS SOUTHEAST
WYOMING TONIGHT...MOSTLY DUE TO FALLING SNOW. NORTHWEST WINDS WILL
GUSTS TO AROUND 30 MPH EAST OF THE LARAMIE RANGE INTO THE NEBRASKA
PANHANDLE TONIGHT...WHICH WILL FURTHER REDUCE VISIBILITES. SNOW
WILL FALL ACROSS SOUTHEAST WYOMING AND NEBRASKA PANHANDLE TONIGHT
WITH SNOW TAPERING OFF FROM SOUTH TO NORTH THROUGH THE DAY MONDAY.
SNOW WILL END ACROSS EAST-CENTRAL WYOMING AND THE NORTHERN
NEBRASKA PANHANDLE MONDAY AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 137 PM MST SUN DEC 14 2014

NO FIRE WEATHER CONCERNS THIS WEEK WITH COLD TEMPERATURES AND HIGH
RELATIVE HUMIDITIES. THERE ARE SEVERAL CHANCES FOR SNOW THROUGH
THE WEEK...WITH THE BEST CHANCE OCCURRING ON MONDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL NOON MST MONDAY FOR WYZ101-102.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST MONDAY FOR WYZ104-105-109-
     112.

     WINTER WEATHER ADVISORY UNTIL 6 PM MST THIS EVENING FOR WYZ110-
     111-113>115.

NE...WINTER WEATHER ADVISORY UNTIL NOON MST MONDAY FOR NEZ002-095-096.

     WINTER WEATHER ADVISORY UNTIL 6 AM MST MONDAY FOR NEZ003-019>021-
     054-055.

&&

$$

SHORT TERM...TJT
LONG TERM...GCC
AVIATION...SML
FIRE WEATHER...TJT


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