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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1519Z Oct 23, 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
1119 AM EDT THU OCT 23 2014

VALID 12Z SUN OCT 26 2014 - 12Z THU OCT 30 2014


...GUIDANCE EVALUATION...

THE 00Z-06Z GFS HAVE ONE OF THE LESS LIKELY PACIFIC/WRN NOAM SOLNS
ALOFT RESULTING FROM A NORTHERN STREAM TROUGH ROTATING AROUND THE
BASE OF THE PERSISTENT CLOSED LOW NEAR 63N 180W SUNDAY 26 OCT.  AS
A RESULT OF THE AMPLIFIED WAVE...THE 00-06Z GFS PRODUCES A CLOSED
LOW NEAR 49N 151 00Z WED 29 OCT...WITH THE ECMWF/CANADIAN GLOBAL
MODELS FURTHER NORTHEAST.

THE MULTI-DAY ENSEMBLE MEANS ARE SUGGESTING A CORE OF POSITIVE HGT
ANOMALIES TO THE SW OF ALASKA AND ALEUTIANS.  TELECONNECTIONS
RELATIVE TO THIS FEATURE FAVOR A POSITIVELY TILTED TROUGH NEARING
THE PAC NW COAST.  THE 00Z/CANADIAN AND ECMWF MEANS TRANSITION
TOWARDS THIS PATTERN TO PROVIDE A LITTLE MORE CONFIDENCE IN THESE
MEANS VERSUS THE 00-06Z GFS AND 00-06Z GEFS MEAN.

THE CLOSED LOW DEVELOPED BY THE 00-06Z GFS RESULTS IN SLOWER
FORWARD MOTION AND TROUGH POSITION FURTHER WEST.  PREFER TO WAIT
UNTIL OTHER MODEL/ENSEMBLES MOVE TOWARDS THIS POSITION BEFORE
GIVING MUCH CREDENCE TO THE GFS FCST.
THE FINAL FCSTS BLENDED THE 00Z ECMWF ENSEMBLE MEAN WITH THE
CANADIAN ENSEMBLE MEAN TIMING.  THE 00Z CANADIAN GLOBAL SFC LOW
PRESSURE MATCHED THE 00Z ECMWF ENSEMBLE MEAN OFF THE PACIFIC
NORTHWEST...BUT WAS OUT OF PHASE WITH OTHER FORECASTS UPSTREAM IN
THE PACIFIC AND DOWNSTREAM IN THE US...SO THE 00Z CANADIAN WAS NOT
USED ELSEWHERE.

THE 06Z GFS AND 00Z ECMWF HAVE COME INTO EXCELLENT AGREEMENT ON
TRACKS FOR THE
EXTRATROPICAL TRANSITION OF ANA...SO A BLEND OF SOLUTIONS WAS USED
DAYS 3-5.
THE 00Z ECMWF WAS AN OUTLIER WITH ITS INTENSE LOW PERSISTING JUST
OFF THE WEST COAST OF CANADA...SO THE MEAN WAS USED TO MITIGATE
THE UNCERTAINTY.

THE MODELS AND ENSEMBLES HAVE BETTER AGREEMENT OVER THE CENTRAL TO
EASTERN US DAYS 3-5...WHERE A 06Z GFS/00Z ECMWF BLEND WITH THEIR
RESPECTIVE 00Z GEFS/00Z ECMWF ENSEMBLE MEANS WAS USED. AGREEMENT
IS GOOD ON LOW PRESSURE DEVELOPING IN THE PLAINS AND MOVING INTO
THE UPPER MS VALLEY MONDAY AND THEN ACROSS THE UPPER LAKES AND
ONTARIO TUE, WITH A TRAILING FRONT MOVING INTO THE OH VALLEY. THE
FRONT THEN PROGRESSES DOWNSTREAM ACROSS THE LAKES AND NORTHEAST,
WITH THE SURFACE REFLECTION WEAKENING FURTHER SOUTH AS THERE ISN'T
MUCH IN THE WAY OF HEIGHT/PRESSURES FALLS IN THE SOUTHERN
APPALACHIANS/SOUTHEAST NEXT WED/THU.

THE 06Z GFS/GEFS GREATER AMPLIFICATION OF THE MID-UPPER TROUGH
ACROSS THE UPPER MS VALLEY NEXT THU 30 OCT APPEARS TO BE A DOMINO
EFFECT DOWNSTREAM FROM THE MORE AMPLIFIED EASTERN PACIFIC
PATTERN...WITH CONFIDENCE LOW IN THESE SOLUTIONS.
ELSEWHERE... A CONSENSUS LOOKS GOOD FOR A CLOSED LOW DEPARTING NRN
NEW ENGLAND ON SUNDAY ACROSS THE CANADIAN MARITIMES. 


...SENSIBLE WEATHER HIGHLIGHTS...

AN AREA FROM THE CNTRL/S-CNTRL PLAINS EWD ACROSS THE MID-UPPER MS
VALLEY INTO THE
GRTLKS SHOULD BE FAVORED FOR SHOWERS/THUNDERSTORMS DURING A PERIOD
CNTRD AROUND TUE.  CONTINUE TO EXPECT WELL ABOVE NORMAL TEMPS
AHEAD OF THE SFC FRONT WITH A COUPLE OF DAYS OF PLUS 10-20F
ANOMALIES FROM THE PLAINS ACROSS THE LOWER-MID MS VALLEY AND INTO
THE TN VALLEY/OH VALLEY.  THE NEGATIVE TEMP ANOMALIES ARE MUCH
MORE LIMITED IN SCOPE...FOCUSING ON THE CENTRAL TO NORTHERN
ROCKIES DAYS 4-5 BEFORE THE AIRMASS WARMS AND REVERTS CLOSER TO
NORMAL VALUES DAYS 6/7.  TEMPS REMAIN ABOVE NORMAL IN THE SOUTHERN
PLAINS THROUGH THE END OF THE PERIOD NEXT THU 30 OCT.

ON WED THE SHOWERS/STORMS PROGRESS ACROSS THE GREAT LAKES/OH
VALLEY/LOWER MS VALLEY AND THEN THE SHOWERS REACH THE EAST COAST
ON THU.

MSTR AND AREAS OF RAIN WILL RETURN TO THE PAC NW/NORTHWEST CA
AHEAD OF THE LOW PRESSURE FORMING FROM THE EXTRATROPICAL MERGER OF
ANA WITH THE MID-LATITUDE PAC SYSTEM. SHOWERS EXTEND INLAND INTO
THE NORTHERN ROCKIES SUN.  ONCE THE MEAN TROUGH AND POTENTIAL
EMBEDDED CLOSED LOW APPROACH THE NORTHWEST NEXT THU 30
OCT...SHOWERS MAY REDEVELOP OVER THE NORTHWEST TO NORTHERN CA
WED-THU.

NO ARCTIC INTRUSIONS SEEM LIKELY FOR SOME TIME TO COME...WITH THE
PRIMARY THREAT  FOR HEAVY SNOW IN THE WASHINGTON CASCADES.

PETERSEN/RAUSCH