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