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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1559Z Jan 23, 2015)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1059 AM EST FRI JAN 23 2015

VALID 12Z MON JAN 26 2015 - 12Z FRI JAN 30 2015

...OVERVIEW...
HIGHLY-AMPLIFIED PATTERN SHOULD PREVAIL THROUGH THE MEDIUM RANGE
FORECAST PERIOD. THIS PATTERN INCLUDES AN ACTIVE EASTERN NORTH
AMERICAN TROUGH AND SURFACE CYCLONE INVOF THE GULF OF MAINE AND
CANADIAN MARITIMES EARLY IN THE PERIOD. A BROAD AND STABLE
UPPER-LEVEL RIDGE ALONG THE WEST COAST OF THE CONTINENT WITH
GRADUALLY BE UNDERCUT/ERODED FROM TWO DIRECTIONS---BY A CUTOFF LOW
OFF THE NORTHWEST COAST OF MEXICO AND A SERIES OF WEAK CYCLONES
MIGRATING NORTHWARD INTO THE EASTERN GULF OF ALASKA . 

...MODEL PREFERENCES...
WILL USE A 23/00Z ECENS/GEFS BLEND FOR THE ENTIRE FORECAST PERIOD
AND A PORTION OF THE DETERMINISTIC ECMWF INTO DAY 6 TO DECIPHER
SOME OF THE SMALLER-SCALE  DETAILS FOR THE LOWER 48. THIS ALLOWS
FOR SOME OF THE BIGGER DIFFERENCES---MAINLY IN THE NORTH CENTRAL
PACIFIC---TO SHAKE OUT WITH RESPECT TO THE UNDERCUTTING NATURE OF
THE PATTERN---TRENDING INTO DAY 8+ FOR THE EAST CENTRAL PACIFIC. 

...UNCERTAINTY ASSESSMENT...
COULD NOT FIND MUCH FAULT WITH THE 23/00Z ENSEMBLE GUIDANCE
(EC/GEFS/NAEFS) THAT WOULD FORCE A BREAK IN CONTINUITY FROM THE
PREVIOUS SET OF WPC MEDIUM RANGE SURFACE/500MB GRAPHICS.

ON OR JUST AFTER DAY 4 (28/00Z)...THE 23/00Z GEFS DOES 'CONTEST'
THE UPPER-LEVEL RIDGE WITH A MORE-CONSOLIDATED SHORTWAVE ENERGY
MIGRATION ACROSS THE COLORADO RIVER BASIN AND 4 CORNERS REGION.
AND THE 23/00Z GEFS IS A SLIGHTLY FASTER SOLUTION ALOFT BETWEEN
70W AND 80W LONGITUDE---WITH THE EASTWARD MIGRATION OF THE 500MB
TROUGH AXIS. THE DIFFERENCES TRANSLATE DOWNSTREAM FROM THE LOWER
MO VALLEY EASTWARD THROUGH THE OHIO VALLEY...WITH A CONSIDERABLE
SPREAD IN THE PLACEMENT OF ONE OR MORE SURFACE REFLECTIONS ALONG
THE LEADING EDGE OF THE 'LATEST' SURGE OF CANADIAN AIR ACROSS THE
EAST CENTRAL UNITED STATES AND FAR WEST CENTRAL ATLANTIC OCEAN.  

NOT SURE BLENDING THE MEANS FOR THE DAY 5-6 SHORTWAVE ENERGY
MIGRATING ACROSS THE CENTRAL ROCKIES AND EXITING ONTO THE CENTRAL
PLAINS---WILL PRODUCE MUCH DETAIL AT THE SURFACE...OTHER THAN TO
GIVE A GENERAL DEPICTION OF THE NEXT CANADIAN SURFACE RIDGE'S
ENTRANCE INTO THE LOWER 48. THE DETERMINISTIC 23/00Z ECMWF WOULD
APPEAR TO ME TO BE A GOOD 'MASS FIELD' COMPROMISE FOR THE FRONTAL
PROGRESSION (LEADING EDGE OF THE SHALLOW CANADIAN AIRMASS
INTRUSION). THIS 'BEST FIT' MAINTAINS THE PREVIOUS WPC GRAPHICS
CONTINUITY THROUGH DAY 6 VERSUS THE 23/00Z DETERMINISTIC
GFS/CANADIAN SOLUTIONS ALONG THIS COLD FRONT. 

CONCERNING THE CUTOFF CIRCULATION MEANDERING TO THE WEST OF BAJA
CALIFORNIA---A BLEND OF THE MEANS FOR DAYS 5-7 MIGHT INDICATE THE
PRESENCE OF A SPLIT-FLOW AND SOUTHERN STREAM INFLUENCE---BUT THERE
IS VERY LITTLE DETAIL NEAR THE SURFACE WITH THE NORTHWARD
"EJECTION" OF INDIVIDUAL SHORTWAVES ALONG THE CALIFORNIA
COAST...SIERRA AND SPREADING INTO THE WESTERN PERIPHERY OF THE
UPPER-LEVEL RIDGE. IN THIS SPLIT-FLOW PATTERN---AND MOVEMENT INTO
A VERY LIGHT MID-LEVEL WIND FIELD---THESE WEAK IMPULSES HAVE
TRAJECTORIES THAT MOVE INTO OREGON COASTAL WATERS AND CENTRAL
ARIZONA.

...SENSIBLE WEATHER HIGHLIGHTS...
THE DAY 3-4 NORTHERN STREAM SYSTEM THAT HAS BEEN A 'TRACK-ABLE'
FEATURE ACROSS THE MID-ATLANTIC REGION WILL TAKE ON SECONDARY
STRENGTHENING OVER THE GULF STREAM WITH LOWER ELEVATION WINTER
P-TYPE DEFORMATION SHIELD ACTIVITY FOR THE NORTHEASTERN
SEABOARD---GENERALLY FROM THE DELMARVA NORTHWARD INTO THE GULF OF
MAINE AND NOVA SCOTIA.

WELL ABOVE NORMAL TEMPERATURES BENEATH THE VERY SLOW MOVING
UPPER-LEVEL RIDGE. THIS ALLOWS MILDER PACIFIC AIR TO SEEP INTO THE
NORTHERN HIGH PLAINS AND MIX DOWNSTREAM INTO THE MISSOURI VALLEY.
IN CONTRAST...BELOW NORMAL TEMPERATURES FOR THE NORTHEAST AND
EASTERN GREAT LAKES...WITH A DEEPER POST-FRONTAL CANADIAN AIRMASS
AND 1040MB+ SURFACE HIGH PROVIDING A SECONDARY SHOT OF COLDER AIR
FOR DAY 7.

VOJTESAK