000 
FXUS02 KWBC 301934
PMDEPD
 
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
233 PM EST MON NOV 30 2009
 
VALID 12Z THU DEC 03 2009 - 12Z MON DEC 07 2009
 
12Z CYCLE UPDATE...

THE PRIMARY CHANGES ON THE 12Z MODEL CYCLE ARE THE MODELS HAVE
AMPLIFIED THE WESTERN ATLANTIC DEEP LAYER RIDGE ON DAY FOUR AND
FIVE...WHICH ALLOWS THE DEVELOPMENT OF A WAVE FURTHER WEST THAN
THE 00Z GUIDANCE SUITE.  SINCE THE 12Z ECMWF/GFS/CANADIAN
GLOBAL/UKMET SHOW A WAVE DEVELOPING...AN UPDATE TO SHOW A LOW
DEVELOPING OVER THE WESTERN ATLANTIC ON SAT DEC 5 IS SHOWN...WITH
THE PRELIM SOLUTION BLENDED WITH THE 12Z ECMWF TO DERIVE THE FINAL
SOLUTION. THE 12Z GFS PARALLEL SHOWS A MAJOR STORM FOR COASTAL NEW
ENGLAND...AND THIS WILL BE A TEST OF ITS SKILL...AS IT IS AN
OUTLIER SOLUTION.

IN THE PACIFIC NORTHWEST AND OFF THE WEST COAST...A WIDE SPREAD OF
SOLUTIONS PERSISTS.  THE 12Z GFS CONTINUES ON THE FAST SIDE WITH A
CLOSED LOW EMERGING FROM THE ROCKIES ACROSS THE NORTHERN PLAINS. 
THIS IS COMPLETELY CONTRADICTED BY THE GFS PARALLEL...WHICH LIKES
THE UKMET/CANADIAN IDEA OF A FURTHER WEST CLOSED 500 MB LOW
DEVELOPING OVER THE NORTHWEST US.  THE 12Z ECMWF TRENDED FURTHER
EAST WITH ITS LOW DEVELOPMENT ON FRI TO EARLY SAT...BUT STALLS THE
LOW OFF THE WEST COAST.  ON SAT-SUN IT MERGES THIS LOW WITH
ANOTHER LOW UNDERCUTTING THE HIGH AMPLITUDE EAST PACIFIC RIDGE AND
PRODUCES A WET PERIOD FOR COASTAL CENTRAL-NORTHERN CA SUN
NIGHT-EARLY MON.  WITH THE MODELS GRADUALLY AGREEING ON THE HIGH
AMPLITUDE CLOSED HIGH ALOFT OVER THE NORTHEAST PACIFIC/ALASKA (500
MB HEIGHTS 2-3 STD DEVIATIONS ABV NORMAL IN THE ECMWF/GEFS
MEANS)...ODDS ARE INCREASING OF A CLOSED LOW DEVELOPING FURTHER
SOUTH OVER THE NORTHWEST/ADJACENT COASTAL WATERS
AND A LIKELY REX BLOCK (HIGH NORTH OF A CLOSED LOW) DEVELOPING. 
FINAL PROGS BLENDED THE PRELIM WITH 30% OF THE 12Z ECMWF TO
PROVIDE BETTER DEFINITION/DEEPER INTENSITY TO THE LOW OFF THE
PACIFIC NORTHWEST/NORTHERN CA COAST.  

PRIOR DISCUSSION...

MODEL AND ENSEMBLE GUIDANCE ALL SHOW PRONOUNCED AMPLIFICATION OF
THE NORTHEAST PACIFIC DEEP LAYER RIDGE.  THIS LEADS TO A
DOWNSTREAM DEVELOPMENT OF A WESTERN US TROUGH AND THE DEVELOPMENT
OF A SFC ANTICYCLONE IN WESTERN CANADA AS A DOME OF COLD AIR
BUILDS IN WESTERN CANADA AND STARTS MOVING INTO THE NORTHWESTERN
US.  THE PRELIMINARY FRONTS AND PRESSURES ARE PRIMARILY A BLEND OF
THE NCEP AND ECMWF ENSEMBLE MEANS...WITH MINORITY CONTRIBUTIONS OF
THE 00Z ECMWF/CANADIAN/UKMET SOLUTIONS.

THE MODELS ARE IN GOOD AGREEMENT ON THE EASTERN US CYCLONE DAYS
3-4 AS IT MOVES NORTH ACROSS NY/NEW ENGLAND AND UP INTO CANADA. 
THE 06Z GFS HAS SLOWED DOWN TO MATCH THE TIMING OF THE
ECMWF/CANADIAN/UKMET/RESPECTIVE ECMWF/NCEP ENSEMBLE MEAN. WITH
GOOD CLUSTERING OF SOLUTIONS...A BLEND OF THE MODELS WAS USED.

THE DIFFERENCES START TO DEVELOP UPSTREAM OFF THE WEST COAST. 
PHASING DIFFERENCES AMONG MODEL/ENSEMBLE SOLUTIONS LEADS TO LARGE
SPREAD OF POSSIBLE SCENARIOS.  WITH INITIAL ENERGY PROGRESSING
FROM THE EASTERN PACIFIC INTO NORTHWEST US... THE 00Z GFS WAS ON
THE FAST EDGE OF GUIDANCE AND WAS NOT USED AS THE 06Z GFS HAS
SLOWED TOWARDS THE TOWARD THE CONSENSUS CLUSTER.  IN ADDITION TO
TIMING DIFFERENCES...THE ECMWF HAS FORMED A DEEPER CLOSED LOW
SFC/ALOFT ON THE WESTERN EDGE OF THE GUIDANCE ENVELOPE THAN THE
GFS/CANADIAN/UKMET/EARLIER ECMWF RUNS AND THE ECMWF ENSEMBLE MEAN.
 7 OF THE 50 ECMWF ENSEMBLE MEMBERS HAVE A CLOSED 500 MB LOW LIKE
THE OPERATIONAL ECMWF...WITH WIDE DISPERSION ACROSS THE NORTHEAST
PACIFIC FRIDAY AND THEN ONSHORE SATURDAY.  A MULTI-MODEL AND
ECMWF/NCEP ENSEMBLE MEAN CONSENSUS WAS USED TO MITIGATE THE
DIFFERENCES.

MULTI-DAY MEANS SUGGEST THE CORE OF POSITIVE HGT ANOMALIES
UPSTREAM SHOULD BE OVER THE GULF OF AK TO THE SOUTHERN AK
COASTLINE... WHICH TELECONNECTS TO A MEAN TROF EXTENDING SOUTHWEST
FROM HUDSON BAY ACROSS THE NORTHERN HIGH PLAINS/ROCKIES INTO THE
GREAT BASIN.  THIS IN TURN SUPPORTS COLDER THAN NORMAL TEMPS IN
THE NORTHWEST US TO THE NORTHERN PLAINS AND EVENTUALLY UPPER MS
VALLEY. CONVERSELY...THIS PATTERN FAVORS THE DEVELOPMENT OF WARMER
THAN NORMAL TEMPS ACROSS THE SOUTHEAST/FL ON DAY SEVEN AND BEYOND.

THE CANADIAN/UKMET AND SEVERAL NCEP/ECMWF ENSEMBLE MEMBERS SHOW
THE DEVELOPMENT OF A NORTHWEST US CLOSED 500 MB LOW SAT...AND THE
06Z GFS BY SUN.  THE CANADIAN MODEL BECOMES THE SOUTHERN OUTLIER
ON SUN DEC 06 AND MON DEC 07.  ON DAYS 4-5...THE CANADIAN IS
INCLUDED WITH THE UKMET AND ENSEMBLE MEANS IN SHOWING DEVELOPMENT
OF THE NORTHWEST US TROUGH.  ON DAY 7...THE CANADIAN WAS
DISCONTINUED IN FAVOR OF GREATER WEIGHTING OF THE MEANS.    

PETERSEN
$$