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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 2056Z Nov 27, 2014)
 
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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
356 PM EST THU NOV 27 2014

VALID 00Z FRI NOV 28 2014 - 00Z MON DEC 01 2014

DAYS 1 TO 3...

...PACIFIC NORTHWEST/NORTHERN ROCKIES/NORTHERN PLAINS/UPPER
MIDWEST...

OVER THE NEXT 3 DAYS...THERE WILL BE QUITE A SHIFT WITH THE UPPER
LEVEL PATTERN ACROSS THE U.S. AS A TROUGH OVER THE EASTERN STATES
CONTINUES TO LIFT NORTHEASTWARD WHILE HEIGHT FALLS OUT WEST HELP
TO REPLACE A RIDGE THERE WITH A TROF.  IN ADDITION...ONE STRONG
SHORTWAVE TROUGH DROPPING SOUTH AND EAST FROM BRITISH COLUMBIA
WILL MOVE ACROSS THE NORTHWEST PORTION OF THE COUNTRY...CREATING
THE POTENTIAL FOR HEAVY SNOW IN THE NORTHWEST MOUNTAINS.

OVER THE NORTHERN PLAINS...COLD AIR OVER THE NORTHERN PLAINS WILL
RETREAT AS WARMER AIR SURGES NORTHWARD. OUT AHEAD OF AN ADVANCING
WARM FRONT...A BAND OF MOSTLY LIGHT SNOW WILL DRIFT EASTWARD 
ACROSS NORTH DAKOTA WITH 1 TO 3 INCHES COMMON AND A LOW
PROBABILITY THAT A FEW AMOUNTS WILL APPROACH 4 INCHES.

OUT WEST...THE REAL THREAT FOR HEAVY SNOW WILL BE FROM LATE FRIDAY
THROUGH LATE SATURDAY.  DURING THAT TIME FRAME...AMOUNTS OF OVER A
FOOT OF SNOW WILL BE LIKELY ACROSS THE CASCADES/BITTERROOTS AND
ESPECIALLY FOR THE ROCKIES IN NW MONTANA. THE HEAVY AMOUNT ARE
RELATED TO THE COMBINATION OF A TROUGH MOVING INTO THE WESTERN
STATES FROM THE EASTERN PACIFIC AND THE SEPARATE TROUGH DROPPING
SOUTHEASTWARD ACROSS SOUTHWESTERN CANADA.

MUCH COLDER AIR WILL DROP SOUTHWARD WITH THE PROGRESSION OF THE
TROUGH MOVING EASTWARD FROM SOUTHWESTERN CANADA FROM LATE FRIDAY
NIGHT INTO EARLY SUNDAY AND THE SIGNIFICANT SNOW WILL ALSO SHIFT
SOUTHEASTWARD ACROSS OREGON INTO THE NORTHERN SIERRA NEVADA RANGE
AS WELL AS EAST INTO CENTRAL IDAHO/SOUTHWESTERN MONTANA AND
NORTHWESTERN WYOMING.

THIS SHIFT IS IN OCCURRING WITHIN THE ENTRANCE REGION OF A
DEVELOPING JET OVER THE NORTHERN ROCKIES RESPONDING TO AN INCREASE
IN CONFLUENT FLOW ACROSS THE NORTHERN TIER OF STATES.

THE PROBABILITY FOR SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN