Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 092137
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 PM EST FRI DEC 09 2016

VALID 00Z SAT DEC 10 2016 - 00Z TUE DEC 13 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.  IN THE WAKE OF SNOW AND PATCHES OF FREEZING RAIN WITHIN
WARM ADVECTION PRECIPITATION LIFTING THROUGH THE
NORTHWEST/NORTHERN ROCKIES FRIDAY...A SERIES OF WEAK PACIFIC
SYSTEMS MOVING INLAND WITHIN FAST PROGRESSIVE FLOW...COMBINED WITH
PERSISTENT ONSHORE FLOW...WILL BRING MULTIPLE ROUNDS OF HEAVY SNOW
OVER THE HIGHER TERRAIN FROM THE PACIFIC NORTHWEST AND NORTHERN
CALIFORNIA TO THE NORTHERN AND CENTRAL ROCKIES.  THE WASHINGTON
AND OREGON CASCADES...SAWTOOTH MOUNTAINS OF IDAHO...TETONS OF
WYOMING...WASATCH/UINTA MOUNTAINS OF UTAH...AND COLORADO ROCKIES
SHOULD ALL SEE SIGNIFICANT ACCUMULATIONS.


...NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY TO THE GREAT
LAKES...OHIO VALLY...CENTRAL APPALACHIANS...AND NORTHEAST...

A SWATH OF ACCUMULATING SNOW IS EXPECTED WITH SHORTWAVE ENERGY
PROGRESSING THROUGH THE NORTHERN TIER OF THE NATION LATER THIS
WEEKEND AND INTO EARLY NEXT WEEK.  SNOW WILL INITIALLY FOCUS IN AN
AXIS OF DEEP-LAYER FRONTOGENESIS SETTING UP OVER THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY SATURDAY NIGHT INTO
SUNDAY...AND INCREASING MOISTURE/WARM AIR ADVECTION AHEAD OF A
SURFACE WAVE LIFTING OUT OF THE MIDDLE MISSISSIPPI VALLEY SHOULD
ALLOW SNOW TO BECOME HEAVIER AND MORE WIDESPREAD AS IT SPREADS
DOWNSTREAM OVER THE GREAT LAKES...OHIO VALLEY...AND EVENTUALLY
CENTRAL APPALACHIANS AND NORTHEAST SUNDAY INTO MONDAY.
ALSO...PERIODS OF SLEET AND FREEZING RAIN WILL BE POSSIBLE TO THE
SOUTH OF THE HEAVIEST SNOW AS THE WARM MOIST AIR OVERRUNS AN
ARCTIC AIRMASS CURRENTLY IN PLACE OVER MUCH OF THE CENTRAL AND
EASTERN U.S..  THERE REMAINS A LOT OF ENSEMBLE SPREAD AND
RUN-TO-RUN FLUCTUATIONS WITH THE SHORTWAVE ENERGY CROSSING THE
NORTHERN TIER...ESPECIALLY AS IT REACHES THE NORTHEAST ON MONDAY
AND A POSSIBLE SURFACE LOW DEEPENS OFF THE NEW ENGLAND
COAST...LEADING TO SOME LOWER CONFIDENCE WITH PRECIPITATION TYPE
AND SNOWFALL TOTALS ACROSS THE CENTRAL APPALACHIANS AND NORTHEAST
LATE IN THE PERIOD.  THE LATEST WPC ENSEMBLE BLEND IS CURRENTLY
KEEPING THE GREATEST CHANCE FOR OVER EIGHT INCHES OF SNOWFALL
WITHIN AN AXIS EXTENDING FROM SOUTHERN MINNESOTA/NORTHERN IOWA TO
SOUTHERN WISCONSIN AND MICHIGAN.

...LAKE EFFECT SNOW...

A COLD AIRMASS BEING ADVECTED OVER RELATIVELY WARMER LAKES WILL
CONTINUE TO FOSTER LAKE EFFECT SNOW BANDS FRIDAY NIGHT AND INTO
SATURDAY.  ACTIVITY SHOULD BEGIN TO DECREASE AS RIDGING BRIEFLY
BUILDS IN ALOFT ON SATURDAY...BUT THEN THE CHANCE FOR SNOW WILL
QUICKLY RETURN TO THE GREAT LAKES WITH WARM ADVECTION
PRECIPITATION MOVING INTO THE REGION ON SUNDAY.  SEE ABOVE SECTION
FOR MORE DETAILS.


THE PROBABILITY OF SIGNIFICANT ICING (GREATER THAN 0.25 INCHES) IS
LESS THAN 10 PERCENT DAYS 1-3.


GERHARDT

$$





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