Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 753 PM EDT Sat Oct 02 2021 Valid 12Z Wed Oct 06 2021 - 12Z Sun Oct 10 2021 ...Pattern Overview and Guidance/Predictability Assessment... Compared to yesterday there is not much change in the forecast pattern and embedded uncertainties. Progressive flow will carry along a series of storm systems that will bring episodes of precipitation and strong winds to areas from the Aleutians/Bering Sea into the western and southern mainland as well as the Panhandle and Gulf of Alaska. During Wednesday-Thursday initial northern Bering Sea low pressure should track northeastward and weaken while a wave develops over the Gulf by early Thursday. There is still a fair degree of uncertainty with the next storm which for now is more likely to track from the western Aleutians into the eastern Bering Sea/western mainland around the end of the week followed by another wave evolving over the Gulf by early Saturday. Then another system may reach the western Aleutians/Bering Sea by next Sunday. An early-period model blend offers good continuity for the low over the northern Bering Sea as of early Wednesday. At the same time this blend (with slight manual adjustment) reflects a northern solution closer to the ensemble means for the Gulf wave as of early Thursday, in contrast to the the latest GFS/CMC which pull the feature farther south. Model/ensemble clustering and spread have stayed remarkably similar over the past 24 hours for the system expected to emerge from the western Aleutians Thursday. GFS/CMC/UKMET runs continue to show varying degrees of strong development with a northeastward track into the eastern Bering Sea by early Friday, while a number of recent ECMWF runs have been weaker and farther south. Latest GEFS means reflect the GFS cluster. CMC/ECens members are more diverse, leading to a weaker depiction in their respective means but those means at least imply a low track similar to the majority cluster. Also of note, operational GFS runs are within the GEFS spread for their very deep low but other models/ensembles suggest the upper dynamics and surface low depth may not be quite as extreme. Minimal change of the guidance distribution compared to yesterday likewise favors maintaining a forecast close to continuity by way of a model blend that leans more toward the majority--albeit a tad weaker given the ongoing uncertainty. Strength of the system will be very sensitive to exactly how the upper support evolves and the medium to smaller scale of the shortwave keeps predictability for several days out in time lower than desired. The aforementioned spread of CMC/ECens members would suggest that potential still exists for a significant shift in the guidance majority at some point. By next weekend the majority cluster maintains continuity for the wave expected to be over the Gulf as of Saturday. Models/means offer a decent signal for another system reaching the western Aleutians/Bering Sea by Sunday, with guidance spread fairly typical for the time frame. A transition to a model/mean blend for this part of the forecast represents the most common guidance ideas and intermediate approach for systems of interest. ...Weather/Hazard Highlights... Initial low pressure over the far northern Bering Sea will maintain a flow of moisture into the western mainland through Wednesday, while precipitation will increase over the southern mainland into the Panhandle as a Gulf of Alaska wave likely develops by early Thursday. The highest totals with this event should be over and near the southern coast/Panhandle but isolated significant totals may also exist over favored terrain in the western mainland. Brisk to strong winds will be possible over the Bering Sea and western mainland and perhaps to a lesser degree over the Gulf with the Thursday wave. Confidence remains only moderate for another vigorous storm which in the more likely scenario would track from the western Aleutians into the eastern Bering Sea/western mainland late in the week followed by low pressure reaching the Gulf by Saturday. This solution would bring meaningful precipitation and/or strong winds across the Aleutians/Bering Sea and into the western mainland, and then bring another period of enhanced precipitation to the southern coast/Panhandle. There is still a lingering lower probability for a weaker and more southern system that would keep any significant moisture/wind to the south of the mainland. Yet another low may reach the western Aleutians/Bering Sea next weekend with accompanying precipitation and enhanced winds. Most of the period will feature below normal high temperatures over the southern mainland and Panhandle while above normal readings prevail over the northern two-thirds of the mainland. The episodes of unsettled weather will lead to warmer anomalies for morning lows, with most locations aside from the Panhandle trending above normal. The greatest warm anomalies for lows should be over the northern mainland late in the 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