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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1558Z Nov 27, 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
1058 AM EST THU NOV 27 2014

VALID 12Z SUN NOV 30 2014 - 12Z THU DEC 04 2014


...HEAVY PRECIPITATION SLOWER TO SPREAD INTO AND INLAND ACROSS THE
WEST COAST...

WHILE RUN TO RUN CONTINUITY FROM GUIDANCE HAS BEEN VERY MUCH LESS
THAN STELLAR RECENTLY...THE MODELS AND ENSEMBLES HAVE MADE SOME
SIGNIFICANT AND SEEMINGLY REASONABLE MID-LARGER SCALE FLOW TRENDS
OVER THE PAST FEW DAYS.

IN THE SRN STREAM...THE GFS/GEFS MEAN AND HIGH RESOLUTION PARALLEL
GFS HAVE TRENDED A BIT LESS PROGRESSIVE WITH ERN PACIFIC MID-UPPER
LEVEL TROUGH ENERGY AND WELL ORGAINZIED SURFACE SYSTEM/HEAVY PCPN
TRANSLATION TO THE WRN US LOOKING BACK OVER THE PAST FEW
DAYS...BUT REMAIN QUITE A BIT MORE PROGRESSIVE THAN OTHER
GUIDANCE. WATER VAPOR IMAGERY AND UPSTREAM FLOW SEEM TO BETTER
SUPPORT A SLOWER PROGRESSION. THE 00 UTC ECMWF ENSEMBLE MEAN HAS
TRENDED MUCH LESS PROGRESSIVE THAN ITS PRIOR 12 UTC RUN AND IS NOW
WELL INTO A SLOWER GUIDANCE CLUSTER. THIS PREFERRED SCENARIO
DELAYS WRN US PCPN ONSET COMPARED TO PRIOR WPC GUIDANCE...BUT A
MIX OF 30% OVERNIGHT WPC WITH 70% 00 UTC ECMWF ENSEMBLE MEAN FOR
CREATION OF OUR SURFACE FRONTS/PRESSURE AND 500 MB PROGS SOFTENED
THE CONTINUITY CHANGE.

IN THE NRN STREAM...DEEP EXTRATROPICAL LOW DEVELOPMENT FROM THE
BERING SEA INTO GULF OF ALASKA SHOULD ACT TO BUILD AN AMPLIFIED
MID-UPPER LEVEL RIDGE OVER WRN CANADA. THIS SHOULD BETTER ALLOW
ENERGY AND LOWER ATMOSPHERIC COLD AIR TO DIG TO THE LEE OF THE
RIDGE TO CARVE OUT A GRADUALLY PROGRESSIVE AND AMPLIFYING NWRN TO
N-CENTRAL TO ERN US MID-UPPER LEVEL TROUGH NEXT WEEK...WITH AMPLE
ROOM TO DIG NOW PROVIDED BY A SLOWER INLAND PROGRESSION OF SRN
STREAM PACIFIC SYSTEM ENERGIES. THIS ALSO OFFERS SOME CONTINUITY
ADJUSTMENT FROM PRIOR WPC GUIDANCE SO AGAIN USED A MIX OF 30%
OVERNIGHT WPC WITH 70% 00 UTC ECMWF ENSEMBLE MEAN TO PRIMARILY
DERIVE OUR SURFACE FRONTS/PRESSURE AND 500 MB PROGS TO SOFTEN THE
CONTINUITY CHANGE THAT IS MOST EVIDENT BY DAYS 6/7 IN ALLOWING A
MORE SUSTAINED PUSH OF COOLING HIGH PRESSURE DOWN BY THEN ACROSS
THE S-CENTRAL AND ERN US ALONG WITH MORE ENHANCED HEAVIER PCPN
POTENTIAL WITH APPROACH OF THE MORE DYNAMICALLY SUPPORTED AND
MOISTURE FOCUSING ASSOCIATED LEAD FRONTAL SYSTEM.

SCHICHTEL