Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 082135
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
434 PM EST THU DEC 08 2016

VALID 00Z FRI DEC 09 2016 - 00Z MON DEC 12 2016


DAYS 1-3...


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

AN ACTIVE PATTERN WILL CONTINUE ACROSS THE WESTERN U.S. THIS
WEEKEND...ESPECIALLY FROM THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA TO THE NORTHERN/CENTRAL ROCKIES.  THE INITIAL FOCUS
WILL BE WITH SNOW AND PATCHES OF FREEZING RAIN DEVELOPING WITHIN
WARM ADVECTION PRECIPITATION LIFTING NORTHEASTWARD THROUGH THE
NORTHWEST AND NORTHERN ROCKIES THURSDAY NIGHT...BUT THEN ATTENTION
SHOULD SHIFT TO PERIODS OF HEAVY SNOW OVER THE FAVORED TERRAIN AS
A CLOSED LOW WEAKENS OFF THE NORTHWEST COAST AND RIPPLES OF
SHORTWAVE ENERGY PROGRESS INLAND WITHIN FAST ZONAL FLOW SETTING UP
ACROSS THE REGION.  THE WASHINGTON AND OREGON CASCADES...SAWTOOTH
MOUNTAINS OF IDAHO...TETONS OF WYOMING....UINTA MOUNTAINS OF
UTAH...AND COLORADO ROCKIES SHOULD ALL SEE SIGNIFICANT
ACCUMULATIONS.


...NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY TO GREAT LAKES AND
OHIO VALLEY...

A SWATH OF ACCUMULATING SNOW IS EXPECTED WITH A RIPPLE OF
SHORTWAVE ENERGY AND POSSIBLE WEAK SURFACE WAVE STREAKING FROM THE
NORTHERN PLAINS TO THE GREAT LAKES AND OHIO VALLEY THIS
WEEKEND...WITH THE HEAVIEST SNOW EXPECTED TO DEVELOP WITHIN A
NARROW AXIS OF DEEP-LAYER FRONTOGENESIS.  MODELS ARE IN AGREEMENT
THAT THE QUICK PROGRESSION OF THE SYSTEM SHOULD KEEP ACCUMULATIONS
LIGHT TO MODERATE...BUT A LARGE AMOUNT OF SPREAD WITH THE EXACT
AMPLITUDE OF THE SHORTWAVE AND DEPTH/TRACK OF THE POTENTIAL
SURFACE WAVE SUGGESTS THERE IS STILL PLENTY OF UNCERTAINTY WITH
THE EXACT LOCATION AND AMOUNTS OF THE HIGHEST SNOWFALL
ACCUMULATIONS (PLEASE REFER TO WPC`S MODEL DIAGNOSTIC
DISCUSSION...PMDHMD...FOR MORE DETAILS ON MODEL SPREAD).  THE
LATEST WPC ENSEMBLE BLEND HAS A SLIGHT RISK AREA (GREATER THAN 10
PERCENT CHANCE) OF GREATER THAN FOUR INCH SNOWFALL ACCUMULATIONS
EXTENDING FROM EASTERN SOUTH DAKOTA AND SOUTHERN MINNESOTA TO THE
GREAT LAKES AND NORTHERN PORTIONS OF THE OHIO VALLEY.  THIS AREA
COULD CERTAINLY SHIFT NORTH OR SOUTH AS MODELS COME INTO BETTER
AGREEMENT.


...LAKE EFFECT SNOW...

COOL NORTHWESTERLY/WESTERLY FLOW OVER RELATIVELY WARMER LAKES WILL
CONTINUE TO FOSTER LAKE EFFECT SNOW BANDS FRIDAY AND INTO
SATURDAY...WITH LOCATIONS WITHIN 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
EXPECTED TO SEE THE HEAVIEST SNOW AND HIGHEST ACCUMULATIONS.  JUST
AS ACTIVITY BEGINS TO DECREASE ON SATURDAY...ADDITIONAL
ACCUMULATING SNOW WILL BE POSSIBLE WITHIN WARM ADVECTION
PRECIPITATION SPREADING INTO THE REGION SATURDAY NIGHT INTO
SUNDAY.


THE PROBABILITY OF SIGNIFICANT ICING (GREATER THAN 0.25 INCHES) IS
LESS THAN 10 PERCENT.


GERHARDT

$$





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