Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 308 PM EDT Sun Sep 02 2018 Valid 12Z Thu Sep 06 2018 - 12Z Mon Sep 10 2018 The deterministic models diverge in details but each shows a highly amplified cutoff pattern as an omega block forams over the northern Pacific with the northern jet stream going over the top of ther Bering Sea ridge in the arctic ocean. The initial upper low in the middle of this week weakens as it drifts towards the british columbia coast and the new model clustering indicates a second center forms over the gulf of AK and drops south into the northern Pacific Fri into Sat 08 Sep. The 12z ECMWF has trended faster south with its low, with a preference ot use the mean to find an intermediate solution between the old and new runs Fri-Sat 08 Sept. The upstream high amplitude closed high over the Bering Sea is slow to move and acts as a block to upstream energy ejecting from northeast Asia. The northern stream on day 7 Sun now shows lower heights over northeast Russia/Siberia extending to Kamchatka and the Bering Straights, supporting formation of a frontal system. In the Arctic Ocean and northern AK, a mid/upper-level Arctic shortwave energy progresses steadily east, allowing a cold front to form and progress across northeast AK into the Yukon. Typical timing and phasing differences with the upper trough exist, with enough clustering to resolve those differences with a multi-model/ensemble mean consensus. Given good synoptic scale pattern agreement and now run to run continuity in the ensemble means, The 12z GFS and 06z GEFS were equally weighted with the 00z ECMWF and the 00z ECMWF ensemble mean. Petersen WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html