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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1727Z Nov 24, 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
1227 PM EST MON NOV 24 2014

VALID 12Z THU NOV 27 2014 - 12Z MON DEC 01 2014

WPC MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS HAVE
BEEN LARGELY DERIVED FROM A BLEND OF THE 00 UTC ECMWF/NAEFS
ENSEMBLE MEANS TO MITIGATE RECENT RUN TO RUN DETRMINISTIC MODEL
MOOD SWINGS IN THE WAKE OF SHORT RANGE. THIS VARIANCE HAVE BEEN
ESPECIALLY EVIDENT IN THE LOWER ATMOSPHERE WITH RESPECT TO OCEANIC
LOW/FRONTAL SYSTEM DEVELOPMENTS OVER THE ERN PACIFIC AND WITH
CANADIAN COLD AIR INTRUSION DEPTH/TIMING OVER THE
NWRN...CENTRAL...AND ERN STATES...BUT EVEN SO HAVE ALSO TRIED TO
INCLUDE SOME DETERMINISTIC MODEL GUIDANCE WITH THE ENSEMBLE MEANS
TO PRODUCE BETTER DETAIL AS WARRANTED.

WITH THE FORMER...ERN PACIFIC SURFACE SYSTEM SPECIFICS REMAIN
UNCERTAIN GIVEN MULTIPLE SUPPORTING IMPLUSES INTO A LINGERING MEAN
MID-UPPER TROUGH POSITION. HOWEVER...THE OVERALL PATTERN WILL BE
FAVORABLE TO MAINTAIN A WET PATTERN ONSHORE SPREADING DOWN THE
WEST COAST AND ACROSS THE NWRN US WITH TIME WHERE THERE MAY BE
MORE INTERACTION WITH WEDGED INTERIOR COLD AIR THAT SEEMS
PLAUSIBLE GIVEN THE POSITION OF AN AMPLIFIED ALASKAN/GULF OF
ALASKA MID-UPPER RIDGE THROUGH LATE WEEK THAT SHOULD ALLOW DECENT
NRN STREAM IMPULSE DIGGING TO THE LEE OF THE FEATURE.

WITH THE LATTER...THE 06 UTC GFS AND 00 UTC ECMWF HAVE COME INTO
BETTER AGREEMENT WITH COLD AIR DELIVERY INTO THE CENTRAL AND ERN
US...BUT SUSPECT THAT A SLIGHTLY MORE RAPID COLD AIR ARRIVAL MORE
IN LINE WITH THE 00 UTC GFS/GFS PARALLEL MIGHT BE MORE LIKELY
GIVEN THE LARGER SCALE FLOW ACROSS MID-HIGH LATITUDES AND
HISTORICAL SLOW MODEL BIAS WITH LOW LEVEL DENSE AIR DELIVERY. THIS
MAINTAINS BETTER WPC CONTINUITY AS WELL DESPITE AMPLE RECENT MODEL
UNCERTAINTY AND ALSO OFFERS A FRONTAL SWEEP ACROSS THE REGION WITH
ORGANIZED BUT MUCH MORE MODEST PCPN POTENTIAL IN THE WAKE OF THE
WETTER LEAD MID-UPPER LEVEL TROUGH AND SURFACE SYSTEM EXITING THE
ERN US DURING THE SHORT RANGE FORECAST PERIOD.

SCHICHTEL