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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 0819Z Dec 19, 2014)
 
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Abbreviations and acronyms used in this product
 
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
319 AM EST FRI DEC 19 2014

VALID 12Z FRI DEC 19 2014 - 12Z MON DEC 22 2014


DAYS 1-3...

...PACIFIC NORTHWEST TO THE NORTHERN AND CENTRAL ROCKIES...

OVERALL THE MODELS ARE IN GOOD AGREEMENT IN BRINGING A SHORTWAVE
AND ITS FRONTAL SYSTEM INTO THE PACIFIC NORTHWEST THIS
MORNING...BEFORE REACHING THE NORTHERN ROCKIES/HIGH PLAINS BY
EARLY SAT.  WHILE THIS SYSTEM IS EXPECTED TO DELIVER LIGHT TO
MODERATE PRECIPITATION ACROSS THE NORTHWEST INTO THE NORTHERN
ROCKIES DURING THE DAY 1 PERIOD...THE BULK OF THE PRECIPITATION IS
EXPECTED TO END BEFORE SNOW LEVELS BEGIN TO DECREASE...LIMITING
THE THREAT FOR WIDESPREAD ACCUMULATIONS EXCEEDING 8-INCHES.  IN
THE WAKE OF THIS INITIAL SYSTEM...MODELS SHOW A SECOND SHORTWAVE
ALONG THE LEADING EDGE OF VERY PROGRESSIVE FLOW MOVING ACROSS THE
NORTHERN PACIFIC...REACHING THE PACIFIC NORTHWEST ON SAT. 
PERSISTENT STRONG DEEP ONSHORE FLOW IS EXPECTED TO DELIVER A
MOISTURE PLUME WITH TROPICAL ORIGINS INTO THE REGION THROUGH THE
REMAINDER OF THE WEEKEND...PRODUCING WIDESPREAD MODERATE TO HEAVY
PRECIPITATION ACROSS THE NORTHWEST INTO THE NORTHERN ROCKIES ON
DAY 2...BEFORE EXTENDING INTO THE CENTRAL ROCKIES BY DAY 3. 
ACROSS THE NORTHWEST...A BUILDING RIDGE ALONG THE WEST COAST WILL
HELP TO CONTAIN THE HEAVY SNOW THREAT TO THE NORTHERN
CASCADES...WHERE A FOOT OR MORE IS POSSIBLE BOTH DAYS.  FURTHER
EAST...THE HEAVY SNOW THREAT IS EXPECTED TO INCLUDE THE
BLUE...SAWTOOTH...SALMON RIVER...BITTERROOT AND TETONS ON DAY
2...EXTENDING FURTHER SOUTH AND EAST INTO THE UINTAS..WASATCH AND
WESTERN CO RANGES ON DAY 3.  WPC QPF AND THERMAL PROFILES FROM THE
NAM...GFS...SREF MEAN AND ECMWF SERVED AS A BASIS FOR THE WPC SNOW
ACCUMULATION FORECASTS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA