Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 645 PM EDT Sat Oct 03 2020 Valid 12Z Wed Oct 07 2020 - 12Z Sun Oct 11 2020 ...Overview and Guidance/Predictability Assessment... Most of the latest models and ensemble means are similar/consistent with the idea of progressive North Pacific flow helping to develop an elongated upper trough over the northeastern Pacific and possibly into the Gulf of Alaska, ahead of a deep north-central Bering Sea storm that will weaken very slowly as it likely tracks toward the coast of the southwestern mainland. By early day 5 Thu consensus still depicts a frontal wave forming near the Alaska Peninsula but after that time agreement remains poor regarding details of this wave and a possible northward-tracking wave ahead of it. Important details are small in scale, leading to continued low predictability. There is a general signal that whatever low pressure exists over the northeastern Pacific into Fri-Sat should trend north/northwest into the Gulf--favored by evolution of troughing aloft and the approach of the Bering Sea upper low. Meanwhile compared to yesterday a number of solutions have changed the depiction of the upper ridge that crosses the mainland mid-late week, forming a closed high that ultimately settles over the Arctic in contrast to a more open ridge from western Canada northwestward. The potential for energy to slide underneath the upper high provides added complexity to the forecast next weekend. A 12Z operational model blend provided good continuity/detail into early day 5 Thu. After that time the forecast began to incorporate 12Z GEFS/00Z ECMWF mean input (reaching 50-60 percent by days 7-8 Sat-Sun) as confidence rapidly decreased for surface details over the Northeast Pacific/Gulf of Alaska. The forecast excluded the 12Z CMC after Thu due to not bringing the Alaska Peninsula wave into the northeastern Pacific and straying south with the Bering Sea upper low. Meanwhile ECMWF input also included some of the old 00Z run mid-late period to downplay the 12Z run that trended faster than consensus with the Bering Sea system. The new 12Z ECMWF mean is quicker to close off an Arctic upper high, supporting trends in the 12Z GEFS/CMC means and recent ECMWF runs/12Z GFS. ...Weather/Threats Highlights... Around midweek the strong Bering storm will be spreading a broad area of precipitation and strong winds across the Aleutians and Bering Sea with some of the leading moisture and brisk winds extending into the far southwestern mainland. From Thu into the weekend there will be potential for one or more areas of focused precipitation within an area from the Alaska Peninsula/Kodiak Island through the southern coast and Panhandle. However predictability and confidence are well below average for important details of one or more surface low centers over the northeastern Pacific/Gulf of Alaska during this time. Therefore it will take additional time to determine the specifics of coverage, duration, and intensity of precipitation. The Aleutians should see unsettled weather with the strong midweek winds trending gradually weaker with time, though still remaining on the brisk side in most cases. Much of the state will see above normal temperatures from Wed through the weekend. The Panhandle is the one likely exception with mostly below normal readings, while some pockets of below normal highs may exist over the southern mainland as well. Anomalies for min temperatures will generally be warmer than those for highs across a majority of the state. 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 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