ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 352 PM EDT TUE OCT 20 2015 VALID 12Z SAT OCT 24 2015 - 12Z WED OCT 28 2015 THE ALASKA MEDIUM RANGE PERIOD FORECAST HINGES UPON THE MIGRATORY REMNANTS OF TYPHOON 25W ('CHAMPI')...ITS PATH ACROSS THE NORTH PACIFIC AFTER DAY 5 AND WHAT WILL BE THE OUTCOME OF THE 'NEW' UPPER-LEVEL CIRCULATION THAT EMERGES FROM ITS EXTRA-TROPICAL TRANSITION. THE COMPLEXITY THAT ENCOMPASSES THE DAY4-6 TRANSITION WINDOW---IS THAT A BROAD AREA OF TROUGHING AND RIDGING...AWAITS ITS ARRIVAL ALONG 50N BETWEEN 160W-170W. THIS ALLOWS FOR A COMPLEX INTERACTION AND STEERING FLOW WITHIN ITS BASE---AND WILL PERIODICALLY GENERATE SECONDARY CYCLOGENESIS---WITH THE INTRODUCTION OF A TROPICALLY-INFUSED MOISTURE AND ENERGY SOURCE. PRIOR TO DAY 5...A SERIES OF MID-LEVEL WAVES...UNRELATED TO 'CHAMPI'... WILL ROTATE IN COUNTER-CLOCKWISE FASHION AROUND A BROAD CYCLONIC CIRCULATION (CURRENTLY NEAR 53N 151W IN THE NORTHWEST GULF). THE 20/00Z FORECAST CYCLE GUIDANCE YIELDED LIMITED CONSENSUS WITH THIS GULF CIRCULATION...AND HOW THE INDIVIDUAL SHORTWAVES INTERACT WITH THE DOWNSTREAM RIDGE. AT FIRST GLANCE...I ALMOST HAVE TO TREAT THIS SCENARIO IN THE GULF (DAY 2-5 TIME FRAME) AS A SEPARATE ENTITY ALTOGETHER---AS THIS CIRCULATION WILL EVENTUALLY BE 'REPLACED' BY THE INTRODUCTION OF CHAMPI'S REMNANTS. BUT 'REPLACED' IS NOT A STRAIGHT-FORWARD DESCRIPTION...I MUST ADMIT. SO THE CHALLENGE IS...FIRST---WHICH SOLUTION OR TREND WILL BECOME OF THE CURRENT CIRCULATION THROUGH DAY 5? AND REGARDLESS OF WHAT UNFOLDS TO ITS WEST BEYOND DAY 5...WHAT WILL THE GULF CIRCULATION LOOK LIKE AS IT SHEARS APART AND DRIFTS EAST-SOUTHEASTWARD TOWARDS THE MAINLAND. THE ANSWER IS--- NOT ACCORDING TO THE DETERMINISTIC 20/00Z CYCLE GUIDANCE---WHY? TOO MUCH EMPHASIS WITH THE 20/00Z CYCLE IN THE GULF AND MAINLAND WAS TIED TOO MUCH TO AND WITH 'OLAF' AND ITS INTERACTION WITH THE MID-LATITUDE FLOW IN PLACE INVOF 35N 145W. AT BEST...THE NAEFS/ECENS MEANS PRODUCED THE GRADUAL EAST-SOUTHEASTWARD DRIFT OF THE CYCLONE...AND WERE CLOSEST TO THE PREVIOUS WPC SURFACE/500MB GRAPHICS. BUT BEYOND DAY 5...THE GULF CIRCULATION NEEDS TO MOVE DOWNSTREAM...IN SOME MEANINGFUL FASHION ---BEFORE--- THAT REPLACEMENT FROM THE WEST (LITERALLY AND FIGURATIVELY) CAN BEGIN. TO GET THERE...THE SERIES OF SHORTWAVES WILL EVENTUALLY HAVE TO FILL AND/OR SHEAR APART THIS CIRCULATION. WHICH LEADS TO THE SECOND CHALLENGE...THE DOWNSTREAM UPPER-LEVEL RIDGE IN PLACE OVER WESTERN CANADA AS A BLOCKING MECHANISM...THAT GRADUALLY MIGRATES NORTHWESTWARD OR FOLDS WESTWARD ACROSS INTERIOR ALASKA THROUGH DAY 5. HERE AGAIN...THE 20/00Z NAEFS/ECENS MEANS DO A BETTER JOB OF FASHIONING THIS RIDGE STRUCTURE AND AMPLITUDE VERSUS THEIR DETERMINISTIC RUNS DO. THE 20/00Z GEFS MEAN WOULD BE THE WEAKEST RIDGE SOLUTION AND THE ECENS THE STRONGEST. FELT THE NAEFS WOULD BE THE BEST MIDDLE-GROUND SOLUTION ALOFT...AND THEREFORE...WOULD ALLOW FOR A BETTER COMPROMISE WITH ITS (THE RIDGE) INTERACTION WITH THE GULF CIRCULATION AND THE EMBEDDED SHORTWAVE ROTATION AND SEQUENCING ACROSS THE ENTIRE GULF---PRIOR TO DAY 5. VOJTESAK