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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 2129Z Dec 07, 2016)
 
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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
429 PM EST WED DEC 07 2016

VALID 00Z THU DEC 08 2016 - 00Z SUN DEC 11 2016


DAYS 1-3...


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

A WIDESPREAD WINTER WEATHER EVENT IS EXPECTED TO IMPACT LOCATIONS
FROM THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE NORTHERN
AND CENTRAL ROCKIES DURING THE LATER HALF OF THE WEEK AND INTO THE
WEEKEND.  ARCTIC AIR CURRENTLY ENTRENCHED ACROSS THE WESTERN U.S.
WILL INITIALLY SET THE STAGE FOR THE EVENT AS WARM MOIST AIR
SURGES INLAND AHEAD OF AN APPROACHING PACIFIC SYSTEM AND OVER THE
ENTRENCHED ARCTIC AIR.  ACCUMULATING SNOW AND PATCHES OF FREEZING
RAIN WILL BE POSSIBLE WITHIN WARM ADVECTION PRECIPITATION
SPREADING NORTHEASTWARD THROUGH NORTHERN CALIFORNIA...PACIFIC
NORTHWEST..AND INTERMOUNTAIN WEST WEDNESDAY NIGHT INTO
THURSDAY....BEFORE SOUTHWESTERLY WINDS DEEPEN DOWN TO THE SURFACE
AND KEEP SNOW CONFINED TO THE HIGHER ELEVATIONS OF THE SIERRA
NEVADA AND CASCADES.  PRECIPITATION WILL CONTINUE TO SPREAD
NORTHEASTWARD THURSDAY INTO FRIDAY...SHIFTING THE FOCUS FOR WINTER
WEATHER INTO THE NORTHERN/CENTRAL ROCKIES.  ALSO...ONCE HEIGHT
FALLS FROM THE APPROACHING PACIFIC SYSTEM BEGIN TO PROGRESS INLAND
OVER THE NORTHWEST FRIDAY NIGHT INTO SUNDAY...INCREASING WINDS AND
LOWERING TEMPERATURES SHOULD SUPPORT ADDITIONAL PERIODS OF HEAVY
SNOW ALONG THE WASHINGTON AND OREGON CASCADES.


...NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY...

SNOW WILL BE POSSIBLE OVER PORTIONS OF THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY ON SATURDAY AS SHORTWAVE ENERGY EJECTS
EASTWARD OUT OF THE NORTHERN ROCKIES.  THE HEAVIEST SNOW AND
HIGHEST ACCUMULATIONS SHOULD BE WITHIN A STRONG FRONTOGENESIS AXIS
SETTING UP TO THE NORTH OF A POTENTIAL SURFACE CYCLONE DEEPENING
OVER THE CENTRAL PLAINS...BUT THERE IS STILL A LOT OF MODEL SPREAD
AND UNCERTAINTY WITH THE TIMING/AMPLITUDE OF THE SHORTWAVE AND
SURFACE CYCLOGENESIS.  THE LATEST WPC ENSEMBLE BLEND KEEPS THE
GREATEST CHANCE FOR SNOW IN A SWATH EXTENDING FROM SOUTH DAKOTA
INTO SOUTHERN MINNESOTA.  PLEASE REFER TO WPC'S MODEL DIAGNOSTIC
DISCUSSION (PMDHMD) FOR MORE DETAILS ON MODEL SPREAD.


...GREAT LAKES...

SNOW SHOWERS ARE EXPECTED DOWNWIND OF THE GREAT LAKES OVER THE
NEXT FEW DAYS AS WINDS INCREASE AND TEMPERATURES DECREASE WITH AN
UPPER TROUGH PROGRESSING FROM THE NORTH CENTRAL TO NORTHEASTERN
U.S..  THE HIGHEST SNOWFALL TOTALS SHOULD BE OVER THE FAVORED NNW
SNOWBELTS IN WESTERN-CENTRAL UPPER MI AND NORTHWEST LOWER MI...AS
WELL AS THE WESTERLY FLOW SNOWBELTS DOWNWIND OF LAKES ERIE AND
ONTARIO.  ACTIVITY SHOULD DECREASE A BIT ON SATURDAY WHILE THE
UPPER TROUGH MOVES OFF THE ATLANTIC COAST AND A SHORTWAVE RIDGE
BRIEFLY BUILDS IN ALOFT.    


GERHARDT