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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0904Z 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
404 AM EST THU NOV 16 2017

VALID 12Z THU NOV 16 2017 - 12Z SUN NOV 19 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 TOTALS (ENDING 12 UTC FRI) ARE EXPECTED TO FOCUS ALONG THE
CENTRAL SIERRA 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 2 FEET OR MORE ACROSS AREAS ABOVE 8000 FT.  VERY
HEAVY TOTALS CAN ALSO BE EXPECTED FURTHER EAST...WHERE LEFT-EXIT
REGION UPPER JET DYNAMICS ARE FORECAST TO BOLSTER AMOUNTS ACROSS
THE SOUTHWEST MONTANA...NORTHWEST WY AND FAR SOUTHEAST ID
RANGES...WHERE WIDESPREAD TOTALS OF A FOOT...WITH LOCALLY HEAVIER
AMOUNTS...CAN BE EXPECTED 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.

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. WHILE AN UPPER RIDGE MOVES ACROSS THE WESTERN THIRD
OF THE CONUS.

...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 THU NIGHT 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.

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 THE
MOUNTAINS OF NORTHERN NEW HAMPSHIRE AND NORTHERN MAINE.

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

PEREIRA