Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 202153
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
453 PM EST FRI JAN 20 2017

VALID 00Z SAT JAN 21 2017 - 00Z TUE JAN 24 2017

DAYS 1-3...

...WESTERN U.S....

AN ACTIVE PATTERN IS EXPECTED TO CONTINUE FOR THE WESTERN
U.S....PARTICULARLY FOR CALIFORNIA OVER THE NEXT 3 DAYS...WITH
HEAVY MOUNTAIN SNOWS AND THE POTENTIAL FOR ADDITIONAL
ACCUMULATIONS EXCEEDING 4 FEET ALONG THE HIGHER PEAKS IN THE
SIERRA.

FOR FRI EVENING EVENING THROUGH THE OVERNIGHT HOURS INTO SAT...A
WELL-DEFINED MID-LEVEL SHORTWAVE/STRONG UPPER JET IS EXPECTED TO
DIG SOUTH OF THE UPPER LOW THAT IS CURRENTLY CENTERED OFF OF THE
PACIFIC NORTHWEST COAST.  ANOMALOUS MOISTURE ADVECTION AFFORDED BY
STRONG SOUTHWESTERLY FLOW AHEAD OF THE ASSOCIATED COLD FRONT
INTERACTING WITH FAVORABLE UPPER JET DYNAMICS WILL HELP SUPPORT
HEAVY SNOWS INTO THE EVENING HOURS ALONG THE SOUTHERN CA COASTAL
RANGES THAT WILL TRANSLATE EAST INTO THE INTERIOR SOUTHWESTERN
U.S. OVERNIGHT...IMPACTING THE MOUNTAINS OF SOUTHERN UT AND
ARIZONA RIM COUNTRY BEFORE REACHING INTO PORTIONS OF NEW MEXICO
AND SOUTHERN CO BY EARLY SAT.  MEANWHILE...PERSISTENT ONSHORE FLOW
WILL CONTINUE TO SUPPORT ADDITIONAL HEAVY SNOWS ALONG THE COASTAL
RANGES OF NORTHWESTERN CA AND SIERRA BEFORE A SHORTWAVE RIDGE
OFFERS A BRIEF RESPITE LATE SAT.

HEAVY PRECIPITATION IS EXPECTED TO RETURN TO NORTHERN CA ON SUN AS
A NEW LOW FORMS OFF OF THE PACIFIC NORTHWEST COAST WITH A STRONG
UPPER JET TO ITS SOUTH EXTENDING INTO NORTHERN CA.  THIS WILL
SUPPORT A FRESH ROUND OF HEAVY SNOWS FOR THE NORTHERN COASTAL
RANGES OF CA INTO THE SOUTHERN CASCADES AND THE SIERRA.  FROM LATE
SUN INTO MON...THE AFOREMENTIONED RIDGE WILL CONTINUE TO GIVE WAY
TO AN AMPLIFYING TROUGH...WITH AN AXIS OF DEEP ONSHORE FLOW
SHIFTING SOUTH ACROSS CA.  AS HEAVY SNOWS CONTINUE ALONG THE
SIERRA...RESIDUAL MOISTURE SPREADING EAST WILL SUPPORT THE
DEVELOPMENT OF LOCALLY HEAVY SNOWS ACROSS OROGRAPHICALLY FAVORED
REGIONS ACROSS THE CENTRAL GREAT BASIN AND PORTIONS OF THE
ROCKIES...INCLUDING THE TETONS...UINTAS...WASATCH AND THE WESTERN
CO RANGES.  AS THE TROUGH CONTINUES TO AMPLIFY...LOCALLY HEAVY
SNOWS ARE EXPECTED TO RETURN TO THE COASTAL RANGES OF SOUTHERN CA
EARLY MON.

DAY 3...

INTERIOR NORTHEAST...

GUIDANCE SHOWS THE SHORTWAVE TROUGH IMPACTING THE SOUTHWESTERN
U.S. FRI EVENING INTO SAT...SHIFTING EAST OF THE SOUTHERN ROCKIES
WITH A CLOSED LOW DEVELOPING OVER THE SOUTHERN HIGH PLAINS SAT
EVENING.  THIS LOW IS EXPECTED TO SPIN ACROSS THE SOUTHERN PLAINS
AND LOWER MS VALLEY ON SUN BEFORE BEGINNING TO LIFT TO THE NORTH
AS IT MOVES ACROSS THE SOUTHEASTERN U.S. EARLY MON.  GUIDANCE
BEGINS TO DIVERGE ON MON WITH RESPECT TO THE TRACK AND AMPLITUDE
OF THE LOW...CONTRIBUTING TO SIGNIFICANT PRECIPITATION TYPE
DIFFERENCES ACROSS THE INTERIOR NORTHEAST SUN NIGHT-EARLY MON.  TO
VARYING DEGREES GUIDANCE SHOWS COOLER AIR ASSOCIATED WITH A
BLOCKING HIGH OVER SOUTHEASTERN CANADA SPILLING SOUTH...OFFERING A
PERIOD OF MIXED PRECIPITATION WITH ACCUMULATING SNOWS ALONG THE
NORTHERN PERIPHERY OF THE PRECIPITATION SHIELD AS IT REACHES INTO
NORTHERN PA...UPSTATE NY AND CENTRAL TO NORTHERN NEW ENGLAND MON
MORNING.  GIVEN THE UNCERTAINTY...THE WPC FORECAST FAVORED AMOUNTS
THAT WERE HEAVIER THAN THE WARMER GFS...BUT ALSO DOWNPLAYED THE
FORECAST FOR HEAVIER AMOUNTS PRESENTED BY THE NAM...THE 09Z
SREFMEAN AND THE 00Z ECMWF.

PEREIRA

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