ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 229 PM EDT THU AUG 27 2015 VALID 12Z MON AUG 31 2015 - 12Z FRI SEP 04 2015 THE PREVIOUS TWO ECENS RUNS AND THE 27/00Z GEFS WERE IN RATHER GOOD AGREEMENT WITH THE MID-LEVEL FLOW PATTERN AND LOW-LEVEL NORTHERN STREAM COLD ADVECTION SEQUENCE ---FOR DAYS 4-5. THE PLACEHOLDER---FOR MUCH OF THE MEDIUM RANGE PERIOD HAS BEEN AND SHOULD CONTINUE TO BE--- THE CIRCULATION FORMALLY KNOWN AS 'ATSANI'. ITS LOCATION NEAR 40N 170E SERVES TO CYCLE SUBTROPICAL MOISTURE NORTHWARD FROM NORTHWEST OF HAWAI'I DOWNSTREAM INTO THE THE NORTHERN STREAM FLOW PATTERN. THE CURRENT FORECASTS DO OCCASIONALLY RECYCLE THIS MOISTURE AND ENERGY---AND IN THE PROCESS--ALLOW SOME SHORTWAVE RIDGING TO MIGRATE THROUGH THE DOWNSTREAM CONFLUENCE AND KEEP SHORTWAVE ENERGY ON 'MORE OR LESS' A SEQUENTIAL MIGRATION PATH FROM THE SOUTHERN YUKON DELTA TO THE OLYMPIC PENINSULA OF WASHINGTON STATE. ESPECIALLY BEYOND DAY 6---THE CHALLENGE IS THE PLACEMENT AND TIMING OF THE SUBTROPICAL ENTITIES INTO THE DOWNSTREAM FLOW. SOLUTIONS WITH SLOWER-MOVING IMPULSES TEND TO PROVIDE MORE AMPLIFICATION/BLOCKING AT HIGHER LATITUDES (MAINLY ALONG 50N). FASTER-MOVING SOLUTIONS KEEP THE FLOW MUCH MORE ZONAL ALONG 50N. GIVEN WHAT IMPACTS THESE SUBTROPICAL IMPULSES HAVE HAD ON THE PREVIOUS 7-10 DAYS WORTH OF FORECASTS ALONG THE DATELINE---WILL CONTINUE WITH THE ECENS MEANS AS 'PLACEHOLDER' FOR DRIVING THE DOWNSTREAM SENSIBLE WEATHER PATTERN...WHICH WILL EVENTUALLY ALLOW THE 'NEW' CIRCULATION TO DRIFT SLOWLY ACROSS THE ALEUTIANS AND SPREAD INTO THE SOUTHERN BERING BY PERIOD'S END.