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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 0745Z Nov 21, 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
245 AM EST TUE NOV 21 2017

VALID 12Z TUE NOV 21 2017 - 12Z FRI NOV 24 2017


DAYS 1-3...

...PACIFIC NORTHWEST/NORTHERN ROCKIES... 
 
AN UPPER RIDGE WILL CONTINUE TO BUILD ACROSS THE WESTERN U.S. ON
TUE...GREATLY LIMITING THE THREAT FOR ANY HEAVY SNOWS OUTSIDE OF
THE HIGHEST PEAKS OF THE NORTHERN CASCADES AND ROCKIES. 
HOWEVER...ENTRENCHED LOW LEVEL COLD AIR MAY SUPPORT A PERIOD OF
FREEZING RAIN ACROSS SOME OF THE INTERIOR LOWLANDS OF THE PACIFIC
NORTHWEST ON TUE...PARTICULARLY ALONG THE EAST SLOPES OF THE
NORTHERN CASCADES WHERE SEVERAL GUIDANCE MEMBERS SHOW LOW LEVEL
EASTERLY FLOW SUPPORTING A STRONG LOW LEVEL INVERSION WITH
SUBFREEZING SURFACE TEMPERATURES.  WPC DAY 1 PROBABILITIES (ENDING
12 UTC WED) INDICATE A SLIGHT RISK FOR ICE ACCUMULATIONS OF A
QUARTER-INCH OR MORE ACROSS THIS AREA. 

WITH THE UPPER RIDGE STILL IN PLACE...THE THREAT FOR WIDESPREAD
HEAVY SNOW WILL REMAIN LIMITED INTO EARLY THU.  THEN ON THU...A
WELL-DEFINED SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT ARE
EXPECTED TO PUSH INTO THE NORTHWESTERN U.S....SUPPRESSING THE
RIDGE AND SUPPORTING A DIP IN SNOW LEVELS ACROSS THE NORTHERN
CASCADES AND ROCKIES.  HEAVIEST ACCUMULATIONS ARE EXPECTED TO
FOCUS ALONG THE NORTHERN CASCADES WHERE WPC DAY 3 PROBABILITIES
(ENDING 12 UTC FRI) SHOW A MODERATE RISK FOR ACCUMULATIONS OF
8-INCHES OR MORE ACROSS AREAS ABOVE 4000 FT.

PEREIRA