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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0810Z Nov 22, 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
310 AM EST SAT NOV 22 2014

VALID 12Z SAT NOV 22 2014 - 12Z TUE NOV 25 2014


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

PASSAGE OF THE SHORTWAVE TROUGH PRESENTLY ENTERING THE PACIFIC
NORTHWEST FOLLOWED BY ANOTHER SHORTWAVE TROUGH WITH A SIMILAR
TRAJECTORY 24 TO 36 HOURS LATER AND THE CORRESPONDINGLY ENHANCED
OROGRAPHIC ASCENT ACCOMPANYING THEIR PASSAGE WILL PROVIDE THE
MAJORITY OF SNOWFALL FOR THE WINDWARD SLOPES OF THE MOUNTAINS FROM
THE PACIFIC NORTHWEST SOUTHEASTWARD TOWARD THE COLORADO ROCKIES
THE NEXT SEVERAL DAYS WITH HEAVY SNOW LIKELY.  THE DETERMINISTIC
TOTALS WERE DERIVED FROM A 3-WAY BLEND OF THE 21Z SREF MEAN ALONG
WITH THE 00Z GFS AND 12Z ECMWF...SUPPORTING MODERATE AND EVEN HIGH
PROBABILITIES OF 8 AND 12 INCHES OF SNOW AT TIMES FROM THE
WASHINGTON AND OREGON CASCADES EASTWARD INTO THE
BITTERROOTS...TETONS...NORTHERN WASATCH..AND COLORADO
ROCKIES...WITH SOME LOCATIONS LIKELY RECEIVE 1 TO 2 FEET OF SNOW.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

UPPER GREAT LAKES...

THE POTENTIAL FOR HEAVY SNOW FOR PARTS OF WISCONSIN AND THE UPPER
PENINSULA OF MICHIGAN MONDAY INTO MONDAY NIGHT HAS INCREASED
SLIGHTLY PER THE LATEST MODEL CONSENSUS AND PREFERRED CAMP OF
SOLUTIONS THAT INCLUDES THE LAST 2 RUNS OF THE ECMWF...THE 12Z
ECMWF ENSEMBLE MEAN...00Z UKMET...AND 00Z PARALLEL GFS...ALL WHICH
SHOW A SUFFICIENTLY DEEPENING SURFACE LOW TRACKING NORTHWARD AS
THE NORTHERN STREAM ALLOWS SUFFICIENTLY COLDER AIR TO ENTRAIN INTO
THE CYCLONE'S CIRCULATION TO HELP GENERATE SNOWFALL PRODUCTION. 
AS IF OFTEN THE CASE...THE PRECISE LOCATION OF THE RAIN/SNOW LINE
WILL LIKELY WAVER THE NEXT COUPLE DAYS...AS WELL AS THE CYCLONE'S
EXACT PATH AND DEPTH...ALL WHICH WILL INFLUENCE THE LIKELIHOOD AND
AMOUNT OF SNOW.  FOR THIS PARTICULAR FORECAST PACKAGE...THE ABOVE
SOLUTIONS WERE USED THE CREATE THE DETERMINISTIC SNOW
AMOUNTS...RESULTING IN LOW AND MODERATE PROBABILITIES OF 4/8..AND
EVEN 12 INCHES OF SNOW FROM JUST WEST OF MARQUETTE TOWARD BUT NOT
QUITE AS FAR SOUTH AS LACROSSE.  EXPECT SOME VARIABILITY IN THE
FORECAST THE NEXT COUPLE DAYS AS MODEL INITIALIZATIONS IMPROVE AND
FORECAST ERRORS DECREASE.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

OHIO VALLEY AND LOWER MICHIGAN...

ALTHOUGH THE PROBABILITIES OF 0.25 OF ICE IS LESS THAN 10 PERCENT
FOR THE NEXT 3 DAYS...THE PROBABILITY OF 0.1 INCHES OF ICE THROUGH
18Z TODAY IS AT LEAST 50 PERCENT IN ASSOCIATION WITH 2 SMALL BUT
POSSIBLY SIGNIFICANT BANDS OF SHOWERS CONTAINING FREEZING RAIN
THAT ARE ENTERING THE REGION.  USED A CONSENSUS OF THE HIGH RES
ARW/NMM AND HRRR TO DEPICT THE ICE TOTALS THAT WERE CONSISTENT
WITH THE OBSERVED 1 TO 3-HOURLY TOTALS EARLIER OVER THE MIDDLE MS
VALLEY AND MIDWEST.  THE HIGHEST AMOUNTS OF ICE ARE EXPECTED TO
OCCUR IN 2 SMALL AREAS...ONE ACROSS MICHIGAN JUST NORTH OF LANSING
AND FLINT...AND ACROSS OHIO...JUST SOUTH OF CLEVELAND.

THE PROBABILITY OF HEAVY SNOW IS LESS THAN 10 PERCENT ALL 3 DAYS.

JAMES