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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0700Z Dec 19, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST FRI DEC 19 2014

VALID 12Z MON DEC 22 2014 - 12Z FRI DEC 26 2014

...AN ACTIVE HOLIDAY WEATHER PATTERN NEXT WEEK...

...GUIDANCE/UNCERTAINTY ASSESSMENT..

WPC MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS HAVE
BEEN PRIMARILY DERIVED FROM THE 12 UTC ECMWF ENSEMBLE MEAN. THIS
OFFERS A BIT MORE AMPLITUDE AND OVERALL CLOSER WPC CONTINUITY
COMPARED TO GFS/NAEFS ENSEMBLE MEANS. THIS SEEMS CONSISTENT WITH
UPSTREAM FLOW AMPLITUDE...BUT WPC PROGS DID HEDGE IN A LITTLE 18
UTC GFS ENSEMBLE MEAN AND 12 UTC NAEFS ENSEMBLE MEAN CONSIDERING
AVERAGE TO BELOW AVERAGE PATTERN PREDICTABILITY. THIS UNCERTAINTY
IS PARTICULARLY EVIDENT IN RECENT DETERMINISTIC MODEL RUN TO RUN
CONTINUITY ISSUES THAT PRECLUDED WPC USAGE.

...PATTERN AND SENSIBLE WEATHER HIGHLIGHTS...

AN AMPLIFIED MID-UPPER LEVEL TROUGH AND PCPN FOCUSING LEAD SURFACE
LOW/FRONTAL SYSTEM DEVELOPS OVER THE CENTRAL US BY EARLY NEXT WEEK
AS EMBEDDED IMPUSLES DIG TO THE LEE OF AN AMPLIFIED ERN PACIFIC
RIDGE ALOFT. THE SUPPORTING AND INCREASINGLY NEG-TILT TROUGH ALOFT
WORKS OVER THE ERN US AND OUT THROUGH THE NERN STATES INTO DAYS
5/6 WED/THU. SUSPECT A THREAT EXISTS FOR ORGANIZED WINTER WEATHER
IN LEAD FLOW OVER A COOLED NRN NEW ENG AIRMASS TUE WITH LOW
INDUCED WRAP-AROUND SNOWS SPREADING FROM THE UPPER MIDWEST AND
GREAT LAKE STATES/MIDWEST LINGERING PAST TUE/WED THAT WORK MORE IN
ERNEST OUT THROUGH THE APPALACHIANS AND MAINLY INTERIOR NRN
MID-ATLANTIC/NERN US ON CHRISTMAS EVE AND CHRISTMAS.

MEANWHILE...NRN/NERN PACIFIC MID-UPPER TROUGH ENERGIES SHOULD WORK
SHARPLY SEWD THROUGH AND TO THE LEE OF AN AMBIENT DOWNSTREAM MEAN
RIDGE POSITION TO SPREAD DYNAMICALLY DRIVEN PCPN INTO THE PAC NW
WED AND FURTHER INLAND ACROSS THE N-CENTRAL INTERMOUNTAIN
WEST/ROCKIES ON CHRISTMAS AND NEXT FRI. THIS WILL INCLUDE A THREAT
FOR MODERATELY HEAVY SNOWS FOCUSING OVER FAVORED INLAND TERRAIN.

SCHICHTEL