ALASKA EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 306 PM EDT SUN OCT 22 2017 VALID 12Z THU OCT 26 2017 - 12Z MON OCT 30 2017 TYPHOON LAN WILL CONTINUE TO MOVE NORTHEASTWARD AND MERGE INTO A NORTHERN STREAM UPPER LOW OVER KAMCHATKA IN THE SHORT RANGE. THAT WILL BE MANIFEST AS THE LOW IN THE SOUTHERN BERING SEA ON THURSDAY WITH THE TRIPLE POINT BECOMING THE NEW PARENT LOW IN THE GULF ON FRIDAY. THE GFS/ECMWF CONTINUE TO WOBBLE AROUND THEIR ENSEMBLE MEANS WITH THE DETAILS AND A BLEND OF THEM OFFER A GOOD STARTING POINT FOR THE FIRST COUPLE OF DAYS OF THE FORECAST. ONCE THE EX-LAN SYSTEM MOVES INTO CANADA, THE PATTERN BECOMES LESS PREDICTABLE REGARDING SYSTEM DEVELOPMENT NEAR THE WESTERN ALEUTIANS. THE ECMWF ENSEMBLES WERE MORE AGGRESSIVE THAN THE GEFS MEMBERS LATE THIS WEEK INTO THE WEEKEND WHICH RESULTS IN ABOUT A 24-36 HR LAG IN THE TROUGH AXIS PAST 160W NEXT SUNDAY. TYPICALLY THE ECMWF ENSEMBLES HANDLE AN AMPLIFIED FLOW PATTERN BETTER THAN THE GEFS MEMBERS, AND GIVEN THAT A BLEND WOULD YIELD A FLATTER FLOW THAN DESIRED, OPTED TO USE THE 00Z ECMWF ENSEMBLE MEAN AS THE BASE FOR THE LAST FEW DAYS OF THE FORECAST, WHICH RESULTED IN A SLOWER PROGRESSION OF THE SYSTEM (WHICH HAS BEEN THE TREND IN RECENT DAYS FOR MOST OF THE SYSTEMS). THE 12Z GFS LIED IN BETWEEN THE QUICKER 06Z GEFS MEAN AND THE 00Z ECMWF ENSEMBLE MEAN WHILE THE 00Z ECMWF WAS SLOWER THAN ITS MEAN, AND NOT DESIRED AT THIS POINT. THEREFORE, THE 00Z ECMWF ENSEMBLE MEAN WAS NICELY PLACED IN BETWEEN THE 12Z GFS AND 00Z ECMWF. FRACASSO