Quantitative Precipitation Forecast
Issued by NWS

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684
FOUS11 KWBC 190805
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 AM EST SUN FEB 19 2017

VALID 12Z SUN FEB 19 2017 - 12Z WED FEB 22 2017

DAYS 1 TO 3...

...RANGES OF THE PACIFIC NORTHWEST/CALIFORNIA/GREAT
BASIN/ROCKIES...

AN ACTIVE PATTERN WILL CONTINUE ACROSS THE WESTERN U.S. THIS
WEEKEND AND INTO EARLY NEXT WEEK...WITH WIDESPREAD SNOW EXPECTED
OVER THE HIGHER ELEVATIONS OF THE PACIFIC
NORTHWEST...CALIFORNIA...GREAT BASIN...AND ROCKIES.  THE HEAVIEST
TOTALS WITH SEVERAL FEET OF SNOW ARE EXPECTED IN THE NORTHERN TO
CENTRAL CA SIERRA NEVADA RANGE. OTHER AREAS OF HEAVY SNOW ARE
EXPECTED WITH AT LEAST A FOOT EXPECTED
OVER THE 3 DAY FORECAST PERIOD SUN - WED MORNING IN THE
CASCADES...SHASTA/TRINITY RANGES...SAWTOOTH...TETONS....WIND
RIVER...AND NORTHERN WASATCH/UINTAS OF UT.

AN AMPLIFIED UPPER TROUGH EDGING INLAND OVER THE SOUTHWEST SUNDAY
WILL PRODUCE A ROUND OF SNOWFALL
OVER HIGHER ELEVATIONS OF THE WASATCH/UINTA MOUNTAINS IN UTAH...AS
WELL AS THE SAN JUAN MOUNTAINS IN SOUTHWEST COLORADO...WHERE
LOCALLY HEAVY AMOUNTS ARE EXPECTED DUE TO LONGER DURATION SNOWS.

ALSO ON SUNDAY A PERSISTENT CLOSED LOW OFF THE WA/VANCOUVER ISLAND
COAST CONTINUES TO SUPPORT WAVES OF ENHANCED MOISTURE AND LIFT
ONSHORE INTO THE PACIFIC NORTHWEST WITH SEVERAL INCHES OF SNOW
EXPECTED IN FAVORED WINDWARD TERRAIN OF THE WA/OR/CA CASCADES.

BY SUNDAY NIGHT INTO MONDAY...ATTENTION WILL QUICKLY SHIFT TO CA
AS AN ATMOSPHERIC RIVER DEVELOPING OVER THE CENTRAL PACIFIC MOVES
INTO THE EASTERN PACIFIC AND IS FORECAST TO MOVE ONSHORE
INTO CA. THE ANOMALOUS FETCH OF PACIFIC MOISTURE AND HIGH 700 MB
MOISTURE ADVECTION AND PROLONGED ASCENT LEADS TO A STRONG SIGNAL
FOR HEAVY SNOWFALL TOTALS ALONG THE SIERRA NEVADA AND
SHASTA/SISKIYOU MOUNTAINS IN NORTHERN CALIFORNIA. THE INLAND
PENETRATION OF THE MOISTURE SURGE BRINGS A DAY OF PROLONGED
SNOWFALL TO THE RANGES OF SOUTHERN ID AND NORTHWEST WY...WHERE A
FOOT OR MORE MAY OCCUR.

ON TUE...THE THREAT FOR HEAVY SNOW OVER THE HIGHER ELEVATIONS OF
NORTHERN TO CENTRAL CALIFORNIA WILL CONTINUE WITH SECONDARY MAXIMA
NORTHEASTWARD INTO THE WINDWARD TERRAIN OF THE BITTERROOT
RANGE/SAWTOOTH MOUNTAINS OF IDAHO AND TETONS IN NORTHWEST WYOMING
AS THE LEADING EDGE OF HEIGHT FALLS AND ASSOCIATED COLD FRONT
PRESS FARTHER INLAND.  THE PERIOD LIKELY STARTS AS SNOW ACROSS THE
WA/OR CASCADES...BUT THE UPPER TROUGH MOVING ONSHORE SHOULD LEAD
TO A TREND TOWARDS DRYING ALOFT WITH WEAKER ASCENT...LEADING TO
LESSENING COVERAGE/INTENSITY OF SNOW SHOWERS BY WED MORNING. THE
WAVE MOVES DOWNSTREAM INTO THE NORTHERN ROCKIES TO PRODUCE A
PERIOD OF MODERATE TO HEAVY SNOW IN THE MOUNTAINS OF THE ID
PANHANDLE TO THE RANGES OF NORTHWEST MT..INCLUDING GLACIER
NATIONAL PARK.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT DAYS
1-3.

PETERSEN



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