Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EDT Mon Oct 05 2020 Valid 12Z Fri Oct 09 2020 - 12Z Tue Oct 13 2020 ...Overview and Guidance/Predictability Assessment... Over the course of the Fri-Tue period, the ensemble means and a reasonable proportion of recent operational models continue to indicate consolidation of initial features (Bering Sea upper low, elongated trough/upper low over the Northeast Pacific/Gulf, energy/closed low reaching the mainland from the northeast) into a mean trough aloft that settles over the mainland. Consensus shows fairly persistent surface low pressure over or near the Gulf of Alaska while low pressure initially over the Bering gradually weakens as it tracks southeastward and then becomes absorbed into the larger scale circulation. There are still embedded uncertainties. In particular the latest GFS runs hold onto the initial Bering system longer than other guidance that loses definition after early Sun. Some of the differences aloft appear fairly subtle and have low predictability several days out in time, so the GFS scenario cannot be ruled out. Still there has been gradual consolidation of guidance for low pressure evolution over the Gulf of Alaska. Meanwhile some of the details remain in doubt but there is reasonable continuity in the general signal for the shortwave energy/possible upper low reaching the mainland from the northeast, encouraged by flow around a weak early-period Arctic upper ridge. The one notable continuity change from yesterday is to provide some reflection of recent GFS/ECMWF/UKMET clustering and continuity for a strengthening mid-latitude Pacific system that may track over or just north of Haida Gwaii around day 6 Sun. Today's forecast blend started with input from the 12Z ECMWF/GFS/UKMET for days 4-5 Fri-Sat. Then the forecast transitioned toward a later-period model/mean blend that incorporated the 12Z/00Z ECMWF runs (more 00Z run) and 12Z GFS along with the 12Z GEFS/00Z ECMWF means. Both ECMWF runs were plausible over/near the mainland but late in the period the new run began to diverge with the larger scale Pacific pattern--albeit with hints reflected in the new ECMWF mean. Some aspects of the CMC were reasonable around the mainland early in the period but elsewhere it strayed significantly from consensus in various ways. ...Weather/Threats Highlights... The evolving pattern aloft and Gulf of Alaska low pressure should support precipitation along the southern coast and Panhandle during most of the period. Best potential for some locally enhanced amounts will be late this week into the weekend. It will be a close call regarding possible effects on the southern Panhandle from the progressive system expected to track near Haida Gwaii around Sun. Lowering heights aloft may produce scattered precipitation at times over the mainland which will be in the gradient between Arctic high pressure and Gulf low pressure. The Aleutians should see brisk and unsettled conditions. Continue to expect above normal temperatures over a majority of the state. The main exceptions remain the Panhandle and some portions of the southern mainland where highs may be modestly below normal. A few isolated near to below normal highs may be possible over the north. Min temperatures will likely be above to well above normal over most areas, except for near to slightly below normal over the Panhandle. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: -No significant hazards are expected over Alaska during this forecast period. WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html