Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 020939
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
439 AM EST FRI DEC 02 2016

VALID 12Z FRI DEC 02 2016 - 12Z MON DEC 05 2016

DAY 1 TO 3...

...PACIFIC NORTHWEST TO THE NORTHERN ROCKIES...

WARM ADVECTION PRECIPITATION ASSOCIATED WITH A SHORTWAVE
APPROACHING BRITISH COLUMBIA IS EXPECTED TO SPREAD ACROSS THE
REGION BEGINNING ON FRI.  THROUGH EARLY SAT SNOW LEVELS ARE
FORECAST TO REMAIN HIGH...WITH THE HEAVY SNOW THREAT EXPECTED TO
REMAIN LARGELY CONFINED TO THE HIGHER PEAKS OF THE NORTHERN
CASCADES.  PRECIPITATION WILL WANE WITH THE PASSAGE OF A SHORTWAVE
RIDGE ON SAT BEFORE THE ARRIVAL OF A BETTER-DEFINED SHORTWAVE AND
A STRONG COLD FRONT THAT IS EXPECTED TO PUSH SOUTH ACROSS THE
REGION ON SUN.  SNOW LEVELS ARE FORECAST TO LOWER APPRECIABLY AS
MUCH COLDER AIR SPILLS ACROSS THE REGION.  THIS IS EXPECTED TO
DELIVER SOME LOWER ELEVATION SNOWS TO THE REGION...WITH SEVERAL
INCHES TO A FOOT OR MORE POSSIBLE BY EARLY MON ACROSS THE HIGHER
TERRAIN OF THE NORTHERN CASCADES...AS WELL AS THE RANGES OF
NORTHERN ID...NORTHWESTERN MT AND NORTHWESTERN WY.  THE WPC
FORECAST UTILIZED WPC QPF AND A BLEND OF GFS/ECMWF DETERMINISTIC
AND ENSEMBLE MEAN THERMAL PROFILES.

...SOUTHERN ROCKIES/SOUTHERN PLAINS...

A SPLIT FLOW PATTERN IS EXPECTED TO PREVAIL ACROSS THE WESTERN
U.S./MEX THIS PERIOD...WITH A MID-UPPER LEVEL CENTER CLOSING OFF
AND DROPPING SOUTHWEST OVER NORTHWESTERN MEX SAT-SUN.  THIS SYSTEM
IS EXPECTED TO BRING MIXED PRECIPITATION TO THE LOWER
ELEVATIONS...WITH SOME OF THE GUIDANCE STILL SHOWING THE POTENTIAL
FOR SEVERAL INCHES OF SNOW ACROSS THE HIGHER MOUNTAINS.  HERE
TOO...THE WPC FORECAST UTILIZED WPC QPF AND A BLEND OF GFS/ECMWF
DETERMINISTIC AND ENSEMBLE MEAN THERMAL PROFILES.  DISCOUNTED THE
NAM AND SREF MEAN...WHICH WERE RELATIVELY SLOW OUTLIERS AND IN
TURN PRODUCED HEAVIER SNOW ACCUMULATIONS ACROSS PORTIONS OF THE
REGION.

...LOWER GREAT LAKES/NEW ENGLAND...

LOW PRESSURE THAT BROUGHT HEAVY SNOW TO PORTIONS OF NORTHERN MAINE
WILL CONTINUE TO LIFT INTO THE CANADIAN MARITIMES.  IN ITS
WAKE...WEAK LOW PRESSURE IS EXPECTED TO MOVE ACROSS SOUTHERN
QUE/NORTHERN NEW ENGLAND WITH A SECONDARY SURGE OF COLDER FORECAST
TO SPILL ACROSS THE NORTHEAST FRI-EARLY SAT.
NORTHWESTERLY-WESTERLY FLOW WILL ENCOURAGE LAKE EFFECT
ACTIVITY/OROGRAPHIC SNOWS EAST OF THE LOWER LAKES INTO THE
NORTHERN APPALACHIANS...WITH ACCUMULATIONS OF 4-INCHES OR MORE
MOST LIKELY ALONG THE TUG HILL INTO WESTERN ADIRONDACK FOOTHILLS.
THE HEAVY SNOW THREAT WILL BE SHORT-LIVED AS RIDGING MOVES ACROSS
THE REGION SAT NIGHT.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA



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