Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Sun Oct 03 2021 Valid 12Z Thu Oct 07 2021 - 12Z Mon Oct 11 2021 ...Confidence Increasing for a Strong Storm to Reach the Southwest Mainland Late This Week... ...Pattern Overview and Guidance/Predictability Assessment... Guidance maintains the progressive and energetic flow that will carry along a series of storm systems from the short term into the extended range period. The strongest extended-range storm should track from the western Aleutians toward/into the southwestern mainland during the latter half of the week. A somewhat weaker system may track across the Bering Sea around Sunday-Monday. Surface lows will also periodically reach/evolve over the Gulf of Alaska in response to the passing dynamics aloft. Expect areas of strong winds and enhanced precipitation to accompany the series of storms. For the western Aleutians to southern mainland system late this week, stronger/northward ECMWF trends over the past day have provided improved guidance clustering compared to previous days. There is still some shuffling among the models for details though. Now the ECMWF/CMC/UKMET are all quite deep, similar to what some earlier GFS runs were showing, and with a track close to Nunivak Island. The ensemble means are reasonably close to this track. On the other hand the latest GFS runs have trended a tad weaker/south versus yesterday's 12Z run. Enough GEFS members are deeper than the operational run to suggest a solution somewhat deeper than the GFS. A slightly enhanced operational model composite yields a surface low depth around 970 mb valid 12Z Friday. The forecast evolution is essentially a deeper version of continuity from the past couple days. The system forecast to track over the Bering Sea by next Sunday-Monday generally shows better than average agreement in principle relative to typical forecasts 7-8 days out in time. There are still various track and detail differences though. The 12Z CMC/GFS and an average of the past two ECMWF runs are generally not far from the ensemble means, so by days 7-8 the forecast blend tempers their solutions with only a modest 30 percent total input of the 12Z GEFS/00Z ECMWF means. The operational model to model/mean blend provides reasonable continuity over the Gulf of Alaska, with one wave early Thursday from leading dynamics and the next one Saturday-Sunday in association with the energy that originally supports the late week Bering Sea storm. ...Weather/Hazard Highlights... The Panhandle may see some lingering precipitation on Thursday with a wave that will track out of the Gulf of Alaska. Some specifics are still a question mark but confidence is gradually increasing for a vigorous storm that should track from the western Aleutians into the eastern Bering Sea/western mainland late in the week. This storm will likely produce a period of strong winds across the Aleutians/Bering Sea and into parts of the mainland, along with a broad precipitation shield covering the Aleutians and approximately the southwest half of the mainland. Some pockets of locally heavy totals are possible. A Gulf wave during the weekend will also focus precipitation along the southeastern coast and Panhandle. Expect a somewhat weaker system to track across the Bering Sea next Sunday-Monday with another episode of precipitation and brisk to strong winds. It is a little early to determine how this system may ultimately affect the mainland. Below normal high temperatures will prevail over the southern mainland and Panhandle through the period. Above normal highs over the northern half to two-thirds of the mainland late this week should steadily trend cooler to yield a mix of above/below normal readings during the weekend and possibly more below normal coverage by next Monday. Low temperatures will be more above normal in general. Northern/northwestern locations may see well above normal lows Thursday into Friday or Saturday with some moderation thereafter. Below normal lows should be confined mostly to portions of the Panhandle but could expand into Southcentral by the start of next week. Rausch Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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