Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 747 PM EDT Fri Oct 01 2021 Valid 12Z Tue Oct 05 2021 - 12Z Sat Oct 09 2021 ...Pattern Overview and Guidance/Predictability Assessment... Expect a progressive and active weather pattern that will bring episodes of significant precipitation to western/southern parts of Mainland Alaska as well as the Panhandle. Individual storms will likely produce areas of strong winds as well. Upper dynamics and possible low pressure initially over the western Aleutians/Bering Sea as of early Tuesday should catch up to and merge with a leading northern Bering storm (extratropical reflection of Typhoon Mindulle) by early Wednesday, followed by development of a Gulf wave by Thursday. Another system should reach near the western Aleutians by Thursday and continue to the east or northeast thereafter, with another wave over the Gulf by next Saturday--whether from triple point development or progression of the initial low. Aside from finer-scale details that have low predictability in the extended time frame, guidance is fairly well behaved for the general scenario of low pressure consolidating over the Bering Sea Tuesday into Wednesday followed by a wave reaching the Gulf of Alaska by early Thursday. A 12Z operational model blend represents consensus well for this part of the forecast. The trailing system that may reach the western Aleutians by early Thursday is more problematic. On average guidance has trended somewhat east/southeast for the late week low track over the past 24-36 hours of runs. However the GFS, 12Z CMC/UKMET, and latest ensemble means (whether explicitly or implied) suggest the past couple ECMWF runs may have become too suppressed. The GFS/CMC/UKMET are all quite strong too. Interestingly the 00Z CMC was similar to the 00Z ECMWF before adjusting to a somewhat faster version of the GFS in the 12Z run. At least the 12Z ECMWF adjusted slower from its 00Z run, narrowing the timing spread among the models. Following a model/ensemble mean blend later in the period yielded a low that was closest to the 12Z CMC in principle (though weaker given the uncertainty) through at least day 7 Friday. Solutions converge for low pressure over the Gulf by early day 8 Saturday. ...Weather/Hazard Highlights... Bering Sea low pressure will spread a broad area of precipitation into the western mainland on Tuesday. Moisture should continue streaming into the west on Wednesday while expanding across the southern coast into the Panhandle Wednesday-Thursday as low pressure develops in the Gulf of Alaska. Highest totals with this event should be over and near the southern coast/Panhandle. Strong winds will be most likely across the Bering Sea/Aleutians and into the far western mainland, with a period of brisk to strong winds also possible around the Gulf system. Latest guidance consensus would have another vigorous storm tracking from the western Aleutians into the western mainland late in the week and low pressure reaching the Gulf by Saturday, producing additional precipitation and strong winds. There is still a lingering lower probability for a more southern track that would keep the significant moisture/wind to the south of the mainland, so confidence is not yet very high regarding specific effects over the southwestern mainland. The forecast pattern should favor below normal high temperatures over the southern mainland and Panhandle through the period. Above normal highs will spread eastward/northeastward across the northern two-thirds of the mainland. Clouds and precipitation will promote warmer anomalies for morning lows, with most locations aside from the Panhandle trending above normal after midweek. Rausch Hazards: - Heavy precipitation across portions of mainland Alaska, Wed, Oct 6. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Wed-Fri, Oct 6-Oct 8. - High winds across portions of mainland Alaska, Mon-Wed, Oct 4-Oct 6. - High winds across portions of mainland Alaska and the Aleutians, Mon-Fri, Oct 4-Oct 8. 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