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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0642Z Dec 21, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
142 AM EST SUN DEC 21 2014

VALID 12Z WED DEC 24 2014 - 12Z SUN DEC 28 2014

...AN ACTIVE HOLIDAY WEATHER PATTERN...

...PATTERN/WEATHER HIGHLIGHTS AND GUIDANCE/UNCERTAINTY
ASSESSMENT...

THE MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR AND
PREDICTABLE LARGER SCALE MID-UPPER LEVEL PATTERN EVOLUTION FOR
MUCH OF THE UPCOMING WEEK. THIS ACTIVE FLOW REGIME GRADUALLY
TRANSITIONS FROM HIGH TO MORE MODEST AMPLITUDE WITH TIME AS AT
LEAST THREE WELL DEFINED MID-UPPER LEVEL TROUGHS AND
ASSOCIATED/UNSETTLING LEAD SURFACE LOW/FRONTAL SYSTEMS AND PCPN
SWATHS PROGRESS STEADILY ACROSS THE LOWER 48.
THE MOST AMPLIFIED/DEEP LEAD SYSTEM WORKS ACROSS THE ERN/NERN US
INTO ERN CANADA CHRISTMAS EVE INTO CHRISTMAS ALONG WITH A SNOW
THREAT FROM THE GREAT LAKES STATES TO THE N-CENTRAL
APPALACHIANS/NRN INTERIOR NERN US AND A MORE MOIST/WARMED AIRMASS
IN ADVANCE OF FRONTAL APPROACH WITH HEAVIEST LEAD QPF POTENTIAL
OVER NEW ENGLAND. MEANWHILE...A SECOND SYSTEM BREACHES THE WEST
COAST/NW US THEN N-CENTRAL GREAT BASIN/ROCKIES CHRISTMAS EVE AND
CHRISTMAS. SUBSEQUENT ENERGY TRANSFER AND SYSTEM REGENESIS OCCURS
OVER THE CENTRAL THEN ERN US FRI-NEXT SUN. A THIRD SYSTEM REACHES
THE NWRN US THEN N-CENTRAL INTERMOUNTAIN WEST/ROCKIES NEXT WEEKEND
TO PROLONG A WET PATTERN WITH TERRAIN FOCUSING HEAVY SNOW THREAT. 
 

SURFACE SYSTEM FORECAST SPREAD AND SENSIBLE WEATHER EMPHASIS SHOWS
MORE VARIANCE/UNCERTAINTY THAN ALOFT OVERALL...BUT THE 12 UTC
ECMWF/ECMWF ENSEMBLE MEAN AND THE EXPERIMENTAL HIGH RESOLUTION 18
UTC GFS PARALLEL SOLUTIONS INTO DAY 5/FRI SEEM BEST CLUSTERED AND
THEIR COMPOSITE IS PREFERRED. A SOLUTION CLOSEST TO THE 12 UTC
ECMWF ENSEMBLE MEAN AND TO A LESSER EXTENT THE 12 UTC ECMWF HOLDS
ONTO A BIT MORE AMPLITUDE THAN THE 18 UTC GFS PARALLEL FRI THROUGH
NEXT WEEKEND. THIS SEEMS TO BETTER FIT UPSTREAM PACIFIC FLOW
AMPLIFICTAION SHOWN COMMONLY BY GUIDANCE BY THEN.

SCHICHTEL