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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2048Z Nov 20, 2014)
 
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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
348 PM EST THU NOV 20 2014

VALID 00Z FRI NOV 21 2014 - 00Z MON NOV 24 2014


DAYS 1 THROUGH 3...


...GREAT LAKES...

HEAVY LAKE EFFECT SNOWS WILL LINGER DOWNWIND FROM LAKES ERIE AND
ONTARIO EARLY IN DAY ONE (THIS EVENING AND OVERNIGHT...WHICH
INCLUDES THE AREA HIT HARDEST BY THIS REGIME IN SWRN NY. ANOTHER
STRONG POLAR/ARCTIC RE-ENFORCING SHORT WAVE TROUGH WILL SWEEP
THROUGH THE GREAT LAKES REGION BEFORE ADVANCING DOWNSTREAM INTO
SERN CANADA. WPC AGAIN UTILIZED QUITE A BIT OF AVAILABLE HIGH
RESOLUTION GUIDANCE FOR THE QPF DETAILS... INCLUDING THE 4KM NAM
CONEST...WRF-ARW AND NMMB...NSSL WRF...AND SSEO MEAN.
PROBABILITIES OF EXCEEDING A FOOT OF ADDITIONAL SNOW (AFTER 00Z)
WILL BE LOCALIZED TO THESE 2 MAIN LONG-AXIS...LAKE PARALLEL BANDS
DOWNWIND FROM LAKE ERIE SOUTH OF BUFFALO AND DOWNWIND FROM LAKE
ONTARIO SOUTH OF WATERTOWN. FOR MORE ON SPECIFIC SNOWFALL
AMOUNTS... PLEASE REFER TO YOU LOCAL WEATHER SERVICE FORECAST
OFFICE.


...PACIFIC NORTHWEST/GREAT BASIN/NORTHERN AND CENTRAL ROCKIES...

BY LATE FRI INTO SAT...A STRONG UPPER-LEVEL JET STREAK AND
ASSOCIATED FLAT SHORTWAVE ENERGY OVER THE NORTHERN PACIFIC (SOUTH
OF THE DEEP LOW OVER THE ALEUTIAN CHAIN) WILL PUSH INTO THE PAC NW
AND EVENTUALLY INTO THE NRN/CEN GREAT BASIN AND NRN/CEN ROCKIES.
BY SUN...THE TROUGH WILL SPLIT INTO 2 STREAMS...WITH THE NORTHERN
STREAM SHORTWAVE TRAVERSING THE NORTHERN PLAINS WHILE THE SOUTHERN
WAVE CROSS THE CENTRAL GREAT BASIN AND CENTRAL/SOUTHERN ROCKIES.
MEANWHILE...YET ANOTHER UPPER JET STREAK/SHORTWAVE TROUGH MOVES
THROUGH THE PAC NW ON SUNDAY. THE ENSUING HEIGHT FALLS AND QG
SUPPORT FOR DEEP-LAYER LIFT...ALONG WITH A WEALTH OF PAC MOISTURE
(ANOMALOUS PWATS) TRANSPORTING INTO THE GREAT BASIN AND
ROCKIES...WILL MAKE FOR AN EXPANDING AREA OF MOD-HEAVY SNOWFALL
WEST OF THE DIVIDE THROUGH THE WEEKEND. THE HEAVIEST SNOWS WILL
AGAIN BE EXPECTED OVER THE HIGHER TERRAIN WITH THE FAVORED UPSLOPE
COMPONENT...FIRST OVER THE WA/OR CASCADE RANGES...WITH SNOW LEVELS
LOWERING BY FRI NIGHT BEHIND THE SURFACE FRONT. THE DEEP-LAYER
FORCING AND UPSLOPE ENHANCEMENT...ALONG WITH THE LOWERING SNOW
LEVELS...WILL BRING MOD-HEAVY SNOWS INTO THE BITTERROOTS AND
BLUE/SAWTOOTH/SALMON RIVER MTNS DOWNSTREAM INTO THE TETONS/WASATCH
AND WRN CO ROCKIES FRI NIGHT INTO THE WEEKEND. OVER THESE
AREAS...THE PROBABILITIES OF EXCEEDING 8 INCHES IN 24 HOURS WILL
BE HIGHEST...ESPECIALLY AFTER 00Z SAT. WPC UTILIZED QUITE A BIT OF
HIGHER RESOLUTION GUIDANCE ACROSS THESE AREAS GIVEN THAT THE MASS
FIELDS OF THE NAM/SREF WERE CLOSE TO THE HIGH RES ECMWF (GFS A BIT
FASTER WITH THE EASTWARD PROGRESSION OF THE INITIAL NORTHERN
STREAM TROUGH...ALONG WITH THE NEXT SHORTWAVE INTO THE PAC NW ON
DAY 3).

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT ALL 3
DAYS. 

HURLEY