Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 070821
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
320 AM EST WED DEC 07 2016

VALID 12Z WED DEC 07 2016 - 12Z SAT DEC 10 2016


DAYS 1-3...


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

A WIDESPREAD WINTER WEATHER EVENT IS EXPECTED FROM THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA TO THE NORTHERN ROCKIES THROUGH
THE END OF THE WEEK. LOW-LEVEL COLD AIR ENTRENCHED ACROSS THE
REGION SHOULD SET THE STAGE FOR THE EVENT AS THE NEXT PACIFIC
SYSTEM APPROACHES THE COAST WEDNESDAY. A BROADENING ZONE OF WARM
MOIST AIR (WARM CONVEYOR BELT) MOVING IN AHEAD OF THE SYSTEM AND
ACROSS THE TOP OF THE COLD AIR IS EXPECTED TO PRODUCE A VARIETY OF
PRECIPITATION TYPES OVER THE PACIFIC NORTHWEST INTO THE
INTERMOUNTAIN WEST...INCLUDING FREEZING RAIN WITH ACCUMULATING ICE
IN THE BASINS...VALLEYS...AND ADJACENT HIGHER SLOPES WHERE THE
COLD AIR REMAINS ENTRENCHED. EASTERLY FLOW IN THE BOUNDARY LAYER
IS EXPECTED TO HELP MAINTAIN THE COLD AIR EAST OF THE CASCADES
BEFORE SOUTHWESTERLY WINDS DEEPEN DOWN TO THE SURFACE. WHILE
WIDESPREAD HEAVY ICE ACCUMULATIONS ARE NOT EXPECTED...SEVERAL
AREAS FROM THE PACIFIC NORTHWEST INTO THE INTERMOUNTAIN WEST MAY
SEE AT LEAST SOME MINOR ICE ACCUMULATIONS LATE WED INTO THU.
MEANWHILE...THE THREAT FOR HEAVY SNOWS IS EXPECTED TO INCREASE
ACROSS THE HIGH SIERRA WED AND WED NIGHT...THEN SPREAD ACROSS THE
HIGHER TERRAIN OF THE NORTHERN CASCADES INTO THE NORTHERN
ROCKIES...TETONS...AND WASATCH RANGE AS THE SYSTEM MOVES INLAND
THURSDAY THROUGH FRI NIGHT.  PLEASE REFER TO WPC`S MODEL
DIAGNOSTIC DISCUSSION (PMDHMD) FOR DETAILS ON THE LARGE AMOUNT OF
MODEL SPREAD AND UNCERTAINTY WITH THIS FEATURE.


...UPPER MIDWEST/GREAT LAKES...

THE UPPER LOW AND DEEP SURFACE CYCLONE THAT BROUGHT BLIZZARD
CONDITIONS TO PORTIONS OF THE NORTHERN PLAINS ON TUESDAY WILL
STEADILY LIFT EAST-NORTHEAST INTO SOUTHERN ONTARIO WEDNESDAY AND
THEN INTO QUEBEC ON THURSDAY. SNOW (MAINLY LIGHT) WILL LINGER
WITHIN THE DEEP TROWAL ZONE AND SHARP MID LEVEL DEFORMATION AXIS
OVER THE UPPER MS VALLEY WEDNESDAY. MEANWHILE...AS THE UPPER LOW
PROGRESSES NORTHEASTWARD AND EVENTUALLY TRANSITIONS TO A BROAD
TROUGH OVER THE GREAT LAKES/NORTHEAST...STRONG COLD AIR ADVECTION
AND DEEP CYCLONIC NORTHWEST TO WEST FLOW WILL SET THE STAGE FOR A
PROLONGED LAKE EFFECT SNOWFALL EVENT...ESPECIALLY 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.

HURLEY

$$





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