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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0805Z May 10, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
405 AM EDT SAT MAY 10 2014

VALID 12Z SAT MAY 10 2014 - 12Z TUE MAY 13 2014

...DAYS 1 TO 3...

...INTERMOUNTAIN WEST INTO THE NORTHERN/CENTRAL ROCKIES...

VIGOROUS AND SLOW MOVING CLOSED LOW CROSSING THE INTERMOUNTAIN
ROCKIES WILL RESULT IN HEAVY SNOWS FROM THE BITTERROOTS AND TETONS
SOUTHWARD INTO THE WASATCH RANGES AND CENTRAL ROCKIES THROUGH
EARLY MONDAY BEFORE WANING ACROSS ALL BUT THE SAN JUANS LATE
MONDAY AS THE LOW POSSIBLY REFORMS FARTHER TO THE SOUTHWEST. 
MODEL TRENDS THE LAST 24 HOURS ARE INDICATIVE OF GROWING
CONFIDENCE IN A HIGH-END SNOW EVENT PARTICULARLY FOR THE CENTRAL
ROCKIES ABOVE 8 TO 9 THOUSAND FEET WHERE 1 TO 2 FEET ARE
LIKELY...WITH 6 TO 12 INCHES ABOVE 6 THOUSAND FEET.  THE MODEL
CONSENSUS HAS HELD FAIRLY STEADY SINCE YESTERDAY WITH AN AVERAGE
OF THE WEAKER AND MORE SOUTHWARD LIQUID EQUIVALENTS OF THE GFS
WITH THE STRONGER AND MORE NORTHWARD LIQUID EQUIVALENTS OF THE
ECMWF MOST PREFERRED WHICH IS CLOSE TO THE UKMET AND ECMWF
ENSEMBLE MEANS...WITH THE GFS TRENDING SLIGHTLY NORTHWARD WITH
TIME AND ECMWF SLIGHTLY SOUTHWARD WITH TIME.  SNOW LEVELS SHOULD
EVENTUALLY FALL TO 4 TO 5 THOUSAND FEET BUT MAY BOTTOM OUT AROUND
2 TO 3 THOUSAND FEET EARLY MONDAY AND AGAIN EARLY TUESDAY WHEN
BOUNDARY LAYER TEMPERATURES ARE AT THEIR LOWEST.  DESPITE IMPROVED
CLUSTERING THIS CYCLE...THE NAM AND SREF MEAN REMAIN THE COLDEST
OUT INTO THE FOOTHILLS...WHICH IS ASSOCIATED WITH LOW CONFIDENCE
GIVEN THEIR OCCASIONAL COLD BIASES.  HOWEVER...THEIR SOLUTIONS
CANNOT BE COMPLETELY RULED OUT IF THE RIGHT MESOSCALE CONDITIONS
CAN DEVELOP.  FOR NOW....WILL EMPHASIZE THE WARMER SOLUTIONS THAT
FOCUS THE HEAVIEST SNOWS ACROSS THE MOUNTAINOUS TERRAIN WITH SOME
BUT NOT AN EXCESSIVE EXTENSION INTO THE FOOTHILLS OF THE CENTRAL
ROCKIES.  REGARDING TIMING AND PROBABILITIES...THE EVENT IS
EXPECTED TO EXPAND ACROSS THE INTERMOUNTAIN WEST TODAY BEFORE
REACHING THE CENTRAL ROCKIES ON SUNDAY AND SUNDAY NIGHT WHEN THE
HEAVIEST SNOWS ARE EXPECTED.  THE FINAL PROBABILITIES DEPICTED
MODERATE PROBABILITIES OF 8 INCHES FOR THE LARAMIE MOUNTAINS
THROUGH 12Z SUNDAY WITH PROBABILITIES OF 8 INCHES EXPANDING ACROSS
THE REMAINDER OF THE CENTRAL ROCKIES NORTH OF DENVER TO NORTH OF
CHEYENNE FOR SUNDAY INTO SUNDAY NIGHT. 

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT FOR
ALL 3 DAYS.

JAMES