Quantitative Precipitation Forecast
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000
FOUS11 KWBC 080853
QPFHSD

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

VALID 12Z THU DEC 08 2016 - 12Z SUN DEC 11 2016


DAYS 1-3...


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

A WIDESPREAD WINTER WEATHER EVENT IS EXPECTED TO IMPACT LOCATIONS
FROM THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE NORTHERN
AND CENTRAL ROCKIES THU INTO THE WEEKEND. ARCTIC AIR CURRENTLY
ENTRENCHED ACROSS THE WESTERN U.S. WILL BE SLOW TO SCOUR OUT OVER
THE NEXT FEW DAYS...WHILE WARM MOISTURE AIR ADVANCING OUT AHEAD OF
AN APPROACHING PACIFIC SYSTEM WILL OVERRIDE THE TRAPPED COLD AIR
AND PRODUCE WINTRY PRECIPITATION DOWN TO TO NEAR SEA OVER THE
PACIFIC NORTHWEST THURSDAY AND THURSDAY NIGHT. ACCUMULATING SNOW
AND PATCHES OF FREEZING RAIN WILL SPREAD NORTHEASTWARD FROM
NORTHERN CALIFORNIA INTO THE PACIFIC NORTHWEST AND INTERMOUNTAIN
WEST BEFORE SOUTHWESTERLY WINDS DEEPEN DOWN TO THE SURFACE AND
KEEP SNOW CONFINED TO THE HIGHER ELEVATIONS OF THE SIERRA NEVADA
AND CASCADES. PRECIPITATION WILL CONTINUE TO EXPAND
EAST-NORTHEASTWARD FRIDAY IN TO THE WEEKEND... SHIFTING THE FOCUS
FOR WINTER WEATHER INTO THE NORTHERN/CENTRAL ROCKIES.
MEANWHILE...CONTINUED WAVES OF LOW PRESSURE ALOFT ALONG WITH DEEP
WESTERLY (ONSHORE) MOIST FLOW WILL SUPPORT ADDITIONAL PERIODS OF
HEAVY SNOW ALONG THE WASHINGTON AND OREGON CASCADES OVER THE
WEEKEND.


...NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY...

THE INITIAL BATCH OF UPPER LEVEL SHORTWAVE ENERGY RESPONSIBLE FOR
THE WINTER WEATHER LATE THIS WEEK ACROSS THE WESTERN U.S. WILL
MOVE QUICKLY INTO THE THE NORTHERN PLAINS AND UPPER MISSISSIPPI
VALLEY OVER THE WEEKEND. THIS SYSTEM WILL BE ACCOMPANIED BY A
RELATIVELY NARROW STRIPE OF DEEP MOISTURE...WHICH WILL IN TURN
GENERATE AN ELONGATED AREA OF LIGHT TO MODERATE SNOW FROM THE
DAKOTAS EAST-SOUTHEAST THROUGH THE UPPER MIDWEST. THE HEAVIEST
SNOW...I.E. PROBABILITIES OF 40-60 PERCENT OF AT LEAST 4
INCHES...IS ANTICIPATED ALONG A NARROW AXIS CORRESPONDING TO THE
STRONGEST DEEP-LAYER FRONTOGENESIS...WHICH AT THIS POINT REMAINS
TOUGH TO PINPOINT (LOW FORECAST CONFIDENCE) GIVEN THE CONTINUED
LATITUDINAL SPREAD AMONG THE 00Z GUIDANCE WITH RESPECT TO THE
WHERE THE MORE FAVORABLE UPPER JET FORCING WILL SET UP ALONG WITH
TIMING/AMPLITUDE DIFFERENCES WITH THE SHORTWAVE AND EVENTUAL
(ALBEIT WEAK) SURFACE REFLECTION. THE LATEST WPC ENSEMBLE BLEND
FOR DAY 3 (12Z SAT-12Z SUN) ESSENTIALLY SPLITS THE DIFFERENCE
BETWEEN THE GFS AND ECMWF...AS THE 00Z ECMWF FINALLY DEPICTS A
SHORTWAVE MOVING INTO THE CENTRAL U.S. (TRENDING TOWARD THE GFS IN
THAT RESPECT)...THOUGH THE ECMWF REMAINS ONE OF THE MORE LIGHTER
RUNS (AMONG BOTH OPERATIONAL AND ENSEMBLE GUIDANCE) WITH RESPECT
TO THE QPF. A PSEUDO-BLEND OF THE GFS-ECMWF-UKMET WAS
UTILIZED...WHICH WAS CLOSE TO THE GFS AS THE WETTER UKMET TENDED
TO OFFSET THE DRIER ECMWF. PLEASE REFER TO WPC`S MODEL DIAGNOSTIC
DISCUSSION (PMDHMD) FOR MORE DETAILS ON MODEL SPREAD.


...GREAT LAKES...

SNOW SHOWERS ARE EXPECTED DOWNWIND OF THE GREAT LAKES OVER THE
NEXT COUPLE OF DAYS AS WINDS INCREASE AND TEMPERATURES DECREASE
WITH AN UPPER TROUGH PROGRESSING FROM THE NORTH CENTRAL TO
NORTHEASTERN U.S..  THE HIGHEST SNOWFALL TOTALS SHOULD BE 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.  ACTIVITY SHOULD DECREASE A BIT ON
SATURDAY WHILE THE UPPER TROUGH MOVES OFF THE ATLANTIC COAST AND A
SHORTWAVE RIDGE BRIEFLY BUILDS IN ALOFT.

HURLEY

$$





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