Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 171952
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
251 PM EST FRI NOV 17 2017

VALID 00Z SAT NOV 18 2017 - 00Z TUE NOV 21 2017


DAYS 1-3...

...CENTRAL ROCKIES TONIGHT...

MID LEVEL CONVERGENCE ASSOCIATED WITH A POSITIVELY-TILTED TROUGH
MOVING ACROSS THE CENTRAL ROCKIES COMBINES WITH WITH LOW TO MID
LEVEL FRONTOGENESIS AND MOIST SOUNDINGS 700-500 MB TO SUPPORT
SEVERAL INCHES OF SNOW ACROSS THE RANGES OF COLORADO TONIGHT.  WPC
DAY 1 PROBABILITIES INDICATING AT LEAST A SLIGHT RISK FOR
ACCUMULATIONS OF 8-INCHES OR MORE FOCUSED ACROSS CENTRAL
COLORADO...INCLUDING THE ELK MOUNTAINS AND SAWATCH RANGE.  SNOWS
ARE EXPECTED TO DIMINISH BY SAT MORNING AS THE TROUGH SHIFTS EAST
INTO THE PLAINS...FOLLOWED BY AN UPPER RIDGE BUILDING ACROSS THE
WESTERN U.S.  THE LIMITED DURATION AND RAPID DRYING ALOFT BY SAT
MORNING LIMIT POTENTIAL FOR HEAVIER SNOWS FOR THIS PERIOD.

...PACIFIC NORTHWEST AND THE NORTHERN ROCKIES...

HEAVY SNOWS ARE EXPECTED TO RETURN TO THE REGION BY LATE SUN AS
ANOTHER POSITIVELY TILTED UPPER TROUGH APPROACHES THE REGION FROM
THE NORTHEAST PACIFIC...DRIVING AN UPPER JET MAX AND DIVERGENCE
MAXIMA INTO THE OLYMPICS AND NORTHERN CASCADES SUN-SUN NIGHT.
HEAVY MOUNTAIN SNOWS ARE LIKELY FROM THE OLYMPICS AND CASCADES
SUNDAY AND THEN CONTINUING INTO THE NORTHERN ROCKIES OF
ID/NORTHWESTERN MT MONDAY.  THE HEAVIEST AMOUNTS ARE MOST LIKELY
OVER THE NORTHERN CASCADES WHERE 1-2 FEET OF SNOW IS EXPECTED. THE
PASSAGE OF THE UPPER TROUGH BRINGS A BREAK IN THE PACIFIC
NORTHWEST LATE MON.

...GREAT LAKES TO THE NORTHEAST...

A SURFACE LOW IS FORECAST TO TRACK NORTHEAST FROM THE OH VALLEY
INTO THE GREAT LAKES AND TENS T LAWRENCE VALLEY SAT NIGHT-SUN.
STRONG LOW LEVEL WARM ADVECTION EAST OF LOW MINIMIZES POTENTIAL
FOR SNOW ACCUMULATIONS IN NEW YORK/NEW ENGLAND. ONLY MINOR SNOW
ACCUMULATIONS ACROSS THE UPPER GREAT LAKES REGION ARE EXPECTED ON
SAT. AS THE LOW LIFTS INTO SOUTHERN QUEBEC ON SUN...STRONG
WEST-NORTHWESTERLY FLOW BEHIND THE TRAILING COLD FRONT WILL
SUPPORT LAKE-EFFECT SNOW SHOWERS...WHICH ARE EXPECTED TO SUPPORT
LIGHT ACCUMULATIONS IN THE LEE OF LAKES ERIE AND ONTARIO. AS THE
LOW LEVEL RIDGE BUILDS IN FROM THE OHIO VALLEY MON...SNOW SHOWER
ACTIVITY SHOULD WIND DOWN.

FOR DAYS 1-3...THE PROBABILITY OF A QUARTER INCH OF ICING IS LESS
THAN 10 PERCENT.

PETERSEN

$$




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