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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2045Z Nov 16, 2017)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 PM EST THU NOV 16 2017

VALID 00Z FRI NOV 17 2017 - 00Z MON NOV 20 2017

DAYS 1 THROUGH 3...

...MOUNTAINS OF CA/PACIFIC NORTHWEST/CENTRAL AND NORTHERN GREAT
BASIN/CENTRAL TO NORTHERN ROCKIES...

HEAVY MOUNTAIN SNOWS FOR THE CASCADES...SIERRA AND PORTIONS OF THE
NORTHERN ROCKIES CAN BE EXPECTED AS A POSITIVELY-TILTED UPPER
TROUGH MOVES INTO THE WESTERN U.S. THU INTO EARLY FRI.  HEAVIEST
DAY 1 ACTIVITY IS EXPECTED TO FOCUS ALONG THE CENTRAL TO SOUTHERN
SIERRA NEVADA IN CA WHERE STRONG SOUTHWESTERLY FLOW AND DEEP
MOISTURE ADVECTION INTERACTING WITH AN UPPER LEVEL DIVERGENCE
MAXIMA IN THE RIGHT-ENTRANCE REGION OF THE JET ARE EXPECTED TO
SUPPORT SNOWFALL ACCUMULATIONS OF 1-2 FEET.  HEAVY TOTALS CAN ALSO
BE EXPECTED IN NORTHWEST WY...WHERE COUPLED JET REGION UPPER JET
DYNAMICS ARE FORECAST TO BOLSTER AMOUNTS...WITH LOCALLY A FOOT OF
SNOW POSSIBLE DURING THE DAY 1 PERIOD.  
AS THE UPPER TROUGH CONTINUES TO SHIFT EAST ON FRI...THE HEAVY
SNOW THREAT IS EXPECTED TO DIMINISH ACROSS THE CASCADES AND
SIERRA...WHILE DROPPING FURTHER SOUTH ALONG THE ROCKIES...WITH
HEAVY ACCUMULATIONS POSSIBLE ALONG THE UINTAS AND WASATCH IN
UTAH...AS WELL AS THE WESTERN COLORADO RANGES.
ON FRI NIGHT...SNOW CONTINUE IN THE RANGES OF CO. BY EARLY
SAT...SNOWS ARE EXPECTED TO COME TO AN END ACROSS MUCH OF THE
WESTERN U.S. AS THE UPPER TROUGH ADVANCES QUICKLY ACROSS CENTRAL
U.S.

SNOW PICKS UP AGAIN SUNDAY IN THE WA OLYMPICS AND NORTHERN
CASCADES AS THE UPPER TROUGH FROM THE EAST PACIFIC
APPROACHES...WITH A FORWARD FLANK JET STREAK AND ASCENT ASSOCIATED
WITH THE LOW LEVEL BOUNDARY AND UPPER DIVERGENCE MAXIMA/LOW LEVEL
MOISTURE FLUX MAXIMA TO SUPPORT A SUSTAINED PERIOD OF LIFT IN THE
MOUNTAINS...WHERE IT IS COLD ENOUGH FOR SNOW. THE MODELS FORECAST
HEAVY PRECIP ON THE CANADIAN SIDE WITH LOCALLY HEAVY TOTALS IN THE
FAVORED TERRAIN THAT SUPPORT POTENTIAL FOR A FOOT OF SNOW AT
HIGHER ELEVATIONS OF THE OLYMPICS/CASCADES SUN.

...NEW YORK/NORTHERN NEW ENGLAND...

LOW PRESSURE FORMING ON A FRONTAL BOUNDARY OFF THE SOUTHERN NEW
ENGLAND COAST ON THU IS FORECAST TO TRACK ALONG THE NEW ENGLAND
COAST AND ACROSS THE CANADIAN MARITIMES TONIGHT INTO FRIDAY. SOME
OF THE MODELS CONTINUE TO SHOW ENOUGH COLD AIR AND MOISTURE FOR
GENERALLY LIGHT SNOW AT THE ONSET OF PRECIPITATION OVER PORTIONS
OF NORTHERN NEW YORK AND NORTHERN NEW ENGLAND WITH THE DEEPENING
WARM ADVECTION AHEAD OF THE MID LEVEL WAVE BEFORE A CHANGEOVER TO
RAIN. ISOLATED POCKETS OF FREEZING RAIN/DRIZZLE ARE POSSIBLE.

A TRANSITION BACK TO SNOW IS POSSIBLE AS THE TRIPLE POINT LOW
DEVELOPS AND LOW LEVEL WINDS SWITCH FROM SOUTHERLY TO
NORTHERLY...SUPPORTING SOME ADDITIONAL ACCUMULATIONS ACROSS
NORTHERN MAINE.

ON SUNDAY...AS THE NEXT LOW PRESSURE SYSTEM CROSSES FROM THE GREAT
LAKES TOWARDS THE ST LAWRENCE VALLEY...
ANOTHER BOUT OF LIGHT MIXED PRECIP IS EXPECTED ACROSS NORTHERN NEW
YORK AND NORTHERN NEW ENGLAND...WITH THE WARM ADVECTION QUICKLY
CHANGING SNOW OVER TO MIXED TYPES AND THEN RAIN.  THE SYSTEM IS
FOLLOWED BY AN OUTBREAK OF COLDER WEATHER SUNDAY...SO LAKE EFFECT
SNOW SHOWERS EXPECTED DOWNWIND FROM LAKES ERIE AND ONTARIO IN
WESTERN/NORTHERN NY AND THE MOUNTAINS IF NORTHERN NEW ENGLAND.

FOR DAYS 1-3...THE PROBABILITY OF GREATER THAN 0.25 INCH OF ICING
IS LESS THAN 10 PERCENT.

PETERSEN