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FOUS11 KWBC 182204
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
500 PM EST SAT DEC 18 2010

VALID 00Z SUN DEC 19 2010 - 00Z WED DEC 22 2010

DAYS 1/2/3...

...WEST...

PERIODS OF HEAVY OROGRAPHIC SNOWFALL ARE EXPECTED TO IMPACT A GOOD
PORTION OF THE WESTERN STATES FROM SAT THROUGH MON. A LARGE AND
SLOW-MOVING CIRCULATION OVER THE NRN/NERN PAC WILL STEER A SERIES
OF DISTURBANCES INLAND. MANUAL GRAPHICS WENT WITH A BLEND OF THE
ECMWF/NAM THROUGH THE FIRST 48 HOURS...THEN MELDED IN SOME 12Z
GFS...TO COVER THE TREND FOR A SUBTLE SOUTHWARD SHIFT OF THE JET
AS THE TROUGH RELOADS OFFSHORE. TREMENDOUS TROPICAL MOISTURE PLUME
ENTERING CALIFORNIA PROCEEDS DOWNSTREAM THROUGH THE INTER-MOUNTAIN
WEST. THE RESULT WILL BE A VERY WET/HEAVY SNOW PACK ACROSS THE
SIERRA... SISKIYOUS...AND OREGON CASCADES EASTWARD INTO
NEVADA...UTAH...NORTHERN ARIZONA AND WESTERN COLORADO. LIQUID
EQUIVALENT PRECIPITATION AMOUNTS ARE ANTICIPATED TO APPROACH 10+
INCHES IN THE SIERRA AND MANUAL GRAPHICS CONSERVATIVELY...FOR THE
THREE DAY PERIOD...ANTICIPATE 1-2 FEET BETWEEN 5000FT-6000FT
MSL...BUT JUST ABOVE THE 6000-6500FT LEVEL...THE AMOUNTS EXPECTED
WILL BE WELL ABOVE 7 FEET. IN THE SISKIYOUS ABOVE 4500 FEET...2-3
FEET IS EXPECTED AND OVER THE WASATCH AND WESTERN COLORADO...3-4
FEET WILL FALL...GENERALLY IN THE 6500-7500FT MSL RANGE.

...EAST CENTRAL NC/SERN VA...
THE 12Z MODEL GUIDANCE IS IN SOLID AGREEMENT WITH A PROGRESSIVE
SRN STREAM SHORTWAVE TROUGH AND INTENSIFICATION OF A SFC WAVE EAST
OF THE OUTER BANKS. TONIGHT...LIGHT SNOWFALL IS EXPECTED NEAR THE
VA/NC BORDER...BEFORE THE SYSTEM SWEEPS OUT TO SEA. GENERALLY 2
INCHES OR LESS IS EXPECTED ACROSS EXTREME SERN VA/NERN NC...WITH A
H85-H7 DEFORMATION AXIS FORMING TO THE NORTHWEST OF THE SURFACE
LOW TRACK. LIGHT SNOWFALL AND FLURRIES MAY EXTEND NORTH ACROSS THE
DELMARVA EARLY SUNDAY MORNING...WITH LITTLE OR NO SIGNIFICANT
ACCUMULATION EXPECTED.

...NORTHERN ROCKIES AND UPPER MIDWEST...
A SERIES OF PACIFIC MID-LEVEL SHORTWAVES ROTATING INLAND ACROSS
THE PACIFIC NORTHWEST WILL MOVE EASTWARD INTO THE NORTHERN ROCKIES
AND OUT ONTO THE NORTHERN PLAINS. A DEEPENING SURFACE WAVE AND
EAST TO SOUTHEAST UPSLOPE FLOW WILL BE INTENSIFYING ACROSS THE
CENTRAL PLAINS IN ADVANCE OF AN ORGANIZING H7 WAVE...WITH
WIDESPREAD SNOWFALL DEVELOPING EAST OF THE DIVIDE ACROSS MONTANA
AND PARTS OF WYOMING. MID-LEVEL WARM FRONT AND GOOD FRONTOGENESIS
DEVELOP ACROSS THE DAKOTAS...AND UPPER MIDWEST ON SUNDAY NIGHT AND
MONDAY...WITH GENERALLY 2-4 INCHES OF SNOWFALL ACROSS THE NORTHERN
PLAINS. WITH THE H7 LOW TRACK EJECTING ESEWD AND A WEAK SFC
REFLECTION MOVING IN TANDEM WITH THE MID-LEVEL LOW...ISENTROPIC
LIFT WILL GENERATE GOOD COLD-SECTOR PRECIPITATION AMOUNTS ACROSS
PORTIONS OF MINNESOTA...WISCONSIN...MICHIGAN AND PORTIONS OF
IA/IL/IN ALONG AND NORTH OF I-80 WITH A SLIVER OF LIGHT FREEZING
PRECIPITATION EXPECTED ALONG THE SOUTHERN EDGE OF THE MOISTURE
LAYER AND LOW-LEVEL INFLOW...ALONG AND JUST SOUTH OF THE I-80
CORRIDOR ACROSS EASTERN NEBRASKA...CENTRAL IOWA AND CENTRAL
ILLINOIS.

...MAINE...
THE SURFACE CYCLONE DEVELOPING EAST OF THE BENCHMARK WILL BECOME
VERTICALLY STACK SOUTHEAST OF NOVA SCOTIA THEN STALL...AND DEEPEN
OVER THE ATLANTIC OCEAN. DEEP ATLANTIC MOISTURE IS EXPECTED TO
WRAP BACK TO THE WEST AND PRODUCE SNOWFALL ACROSS MAINE ON DAY 3.
MANUAL GRAPHICS SIDED WITH A BLEND OF THE GFS/NAM/ECMWF WITH HPC
QPFS HINTING AT 1/2 INCH LIQUID EQUIVALENTS FROM THIS DEEPENING
CYCLONE. THIS TRANSLATES TO 4-8 INCHES OF SNOW WITH HEFTY
SNOWFALLS ALONG AND JUST INLAND OF THE SOUTHEAST COAST.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

VOJTESAK
$$