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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0738Z Nov 21, 2014)
 
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PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 AM EST FRI NOV 21 2014

VALID 12Z FRI NOV 21 2014 - 12Z MON NOV 24 2014


PACIFIC NORTHWEST/GREAT BASIN/NORTHERN AND CENTRAL ROCKIES...

ALTHOUGH SOME TIMING AND STRENGTH DIFFERENCES REMAIN APPARENT
WITHIN THE LATEST GUIDANCE...MODELS ARE IN GENERAL AGREEMENT THAT
PERIODIC MODERATE AND EVEN HEAVY SNOWS WILL OVERSPREAD THE
MOUNTAINS OF THE PACIFIC NORTHWEST INTO THE GREAT BASIN AND
ROCKIES THE NEXT SEVERAL DAYS...WITH THE HIGHEST RATES OCCURRING
DURING THE PASSAGE OF 2 SHORTWAVE TROUGHS.  THE FIRST TROUGH
CROSSES THE PACIFIC NORTHWEST LATER TODAY...WHILE THE SECOND
ARRIVES OVER THE PACIFIC NORTHWEST EARLY SUNDAY...BOTH MOVING EAST
SOUTHEASTWARD...WITH SNOW LEVELS FLUCTUATING AS THEY PASS BUT
GENERALLY LOWERING FROM SUNDAY INTO EARLY MONDAY.  GIVEN THE
INFLUENCE OF OROGRAPHIC ASCENT WITH THESE SNOW EVENTS...HAVE
CONTINUED TO RELY UPON THE HIGHER RES GUIDANCE AND THE PREVIOUS
FORECAST FOR DETERMINING THE LIQUID EQUIVALENTS AND THERMAL
PROFILES THROUGH EARLY SATURDAY...
BEFORE THE INCREASING SOLUTION SPREAD AND ACCOMPANYING UNCERTAINTY
SUPPORT MORE WEIGHTING OF THE TYPICALLY MORE ACCURATE GFS AND
ECMWF SOLUTIONS...WHICH FORMED THE BASIS FOR SUNDAY INTO MONDAY. 
THE RESULT IS LOW TO MODERATE PROBABILITIES OF 8 AND 12 INCHES OF
SNOW ACROSS THE WASHINGTON AND OREGON CASCADES EXTENDING INTO THE
SAWTOOTH RANGE FOR TONIGHT...BEFORE SPREADING FURTHER INLAND TO
AFFECT THE WINDWARD SLOPES OF MORE OF THE
BITTERROOTS...TETONS...NORTHERN WASATCH...AND EVENTUALLY THE
CENTRAL ROCKIES...WHERE LOW TO MODERATE PROBABILITIES OF 8 AND 12
INCHES OF SNOW ARE ALSO DEPICTED.

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

JAMES