Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 641 PM EDT Fri Oct 02 2020 Valid 12Z Tue Oct 06 2020 - 12Z Sat Oct 10 2020 ...Overview and Guidance/Predictability Assessment... Today's guidance shows remarkably good agreement and continuity for the general pattern during the period while some typical detail uncertainties arise by the latter half of the forecast. Strong and massive low pressure should track across the far western Bering Sea through midweek and then gradually weaken as it drifts into the north-central/east-central Bering. As progressive North Pacific flow begins to promote elongated upper troughing to the southeast of the parent system, consensus develops a frontal wave near the Alaska Peninsula or Kodiak Island with low pressure persisting over the northeastern Pacific/Gulf area into next Sat. Ahead of this evolution expect initial low pressure near the Kenai Peninsula to weaken Tue-Wed before dissipating, while an upper ridge likely progresses from the Bering Sea across the mainland and ends up extending from western Canada northwestward into the Arctic by next Sat. From day 4 Tue into early day 6 Thu a 12Z operational model blend represented consensus well and with good detail. During the rest of the period the primary uncertainty involved the specifics of low pressure to the southeast/east of the Alaska Peninsula. Operational models have displayed various ideas for evolution of the wave that develops from the parent system's front, as well as for interaction among the frontal wave and another wave that may lift northward ahead of it. The importance of subtle details will likely give this evolution fairly low predictability for a while, favoring a transition from the earlier operational model blend toward an even mix of models (12Z GFS/ECMWF) and means (12Z GEFS/00Z ECens) by day 8 Sat. The 12Z CMC strayed to the northern side of the spread by the latter half of the period so it was phased out of the forecast by Fri-Sat. ...Weather/Threats Highlights... Weakening low pressure initially near the Kenai Peninsula may support lingering mostly light precipitation along the southern coast and Panhandle through Tue. Other parts of the eastern half of the mainland may see light/scattered activity as well. Meanwhile the strong Bering storm will spread a broad area of precipitation and strong winds across the Aleutians and Bering Sea Tue-Wed. Some of the leading moisture and brisk winds may reach the far western mainland by Wed-Wed night. During the late week/weekend time frame the evolving pattern aloft and low pressure to the southeast/east of the Alaska Peninsula will tend to favor precipitation over the Peninsula/Kodiak Island and southern coast/Panhandle. Coverage, duration, and intensity of precip will depend on low-predictability specifics of the one or more low pressure centers. Winds across the Aleutians will moderate somewhat with time as the Bering Sea low trends gradually weaker. Expect a majority of the state to see above normal temperatures during the period. The Panhandle and some portions of the southern mainland may see modestly below normal highs. Min temperatures should be above climatology nearly state-wide with anomalies tending to be greatest over central/northern locations. 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: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon, Oct 5. 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