Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Mon Oct 28 2024 Valid 12Z Fri Nov 01 2024 - 12Z Tue Nov 05 2024 ...Stormy pattern late this week into next with potential for multiple episodes of significant precipitation/wind from the Aleutians eastward... ...Overview... Latest guidance has actually become more diverse for specifics compared to 24 hours ago, but continues to advertise an active pattern with at least a couple windy and precipitation-focusing storm systems that may affect areas from the Aleutians to the southern coast/Panhandle. A leading storm should reach near the eastern Aleutians/Alaska Peninsula by Friday with a northeastward or eastward track thereafter. There is a subset of models developing a trailing central Pacific wave that reaches the northeastern Pacific/southern Gulf of Alaska by early next week, but a better and more coherent signal exists for stronger North Pacific/Aleutians/Alaska Peninsula development next Monday-Tuesday. This latter storm should have some input from current Typhoon Kong-rey and progressive mid-latitude dynamics but with the models/ensembles displaying ambiguous details for how this development will occur over the western Pacific. Over Mainland Alaska, an upper weakness will likely settle over northern areas for a time while details over the south will depend on the Friday into weekend storm. By next Tuesday, broader southerly flow or upper ridging may set up ahead of next week's potential Aleutians storm. ...Guidance Evaluation/Preferences... Clustering and continuity remain good for the slowly weakening low over the central/western Bering Sea into Friday and the weak Gulf of Alaska wave that should be dissipated by Saturday. Beyond early Friday there is still spread for the Bering Sea low that may wobble to the west or south, with specifics having low predictability. Over the past day the forecast spread has increased for the deep North Pacific storm expected to be near the eastern Aleutians/Alaska Peninsula by Friday. Looking at guidance through the arrival of the operational 12Z ECMWF run, CMC/CMCens/ICON and ECens mean runs have been persistent with an eventual track into the southeastern Bering Sea/western coast of the mainland as upper dynamics lift into this region and become part of the larger scale mean low aloft. In contrast, recent GFS runs have been notably faster--plus trending farther south in the 06Z/12Z/18Z runs, to the extent of tracking the storm to the southern Panhandle or Haida Gwaii, as dynamics push rapidly eastward instead. GEFS mean runs had been part of the Bering Sea cluster but had recently started stretching out to reflect some Gulf members, with the 12Z run shifting to a farther north version of the GFS. The UKMET run leans fast as well but is north of the GFS. 00Z/06Z machine learning (ML) models reflected most of this spread while a slight majority favored a northern Gulf/coastal track. ECMWF runs have been the most stable over the past day or so, and were preferred today as a reasonable intermediate solution closest to continuity given the existing spread--though with some reservations that it could be a little slow/north. The 12Z ML models and 18Z ICON suggest increasing potential for a track near the Alaska Peninsula then Kodiak Island and the northern Gulf/southern coast. Of particular note, the 12Z AIFS adjusted to this idea after persistently being part of the Bering Sea cluster in previous runs. Behind this system, latest GFS/CMC runs and the 12Z ICON develop a central Pacific wave that tracks into the northeastern Pacific/southern Gulf of Alaska. The 06Z GEFS mean reflected such a wave but the 12Z version toned it down, while other models and ensemble means plus ML models offer very little support for this system. The preference is to avoid depicting this feature until there is a more pronounced shift in guidance clustering. Recent guidance runs have been varying for how to handle what remains of current Typhoon Kong-rey after the system passes through Taiwan. However they have been showing the general theme of this system (in weakened form) and/or a wave breaking off immediately to its northeast developing under the influence of progressive mid-latitude energy, leading to potentially strong low pressure reaching the North Pacific/Aleutians/Alaska Peninsula region by next Monday-Tuesday. An average of GFS runs/12Z ECMWF along with the latest ensemble means would offer a reasonable intermediate position, though per recent tendencies the GEFS mean is weaker than other means. A depth between the GFS/ECMWF and the means is a reasonable starting point while awaiting better convergence in details. Recent runs of ML models show a potential for slightly faster progression. Preference for an intermediate/continuity solution for the leading storm Friday into the weekend led to starting with a blend of the 12Z/00Z ECMWF runs and yesterday's continuity Friday into Sunday. Then the forecast transitioned toward 40 percent 12Z ECMWF and the rest 12Z GEFS/CMCens and 00Z ECens means by next Tuesday. ...Weather/Hazards Highlights... A weak and dissipating wave/frontal system tracking over the Gulf may push some light precipitation into the Panhandle Friday. Then expect a deep North Pacific storm to reach near the eastern Aleutians/Alaska Peninsula by Friday, bringing the potential for high winds and precipitation to that region and surrounding waters. Track uncertainty continues thereafter, with the most likely range between the southern mainland and Gulf of Alaska. This would support a period of brisk winds and meaningful precipitation along the southern coast into the Panhandle into the weekend. In terms of hazards, there is relatively better confidence in the potential for high winds over the eastern Aleutians and western Alaska Peninsula Friday into Saturday with this region highlighted in the Days 3-7 Hazards Outlook. Lower confidence in specifics and/or wind and precipitation remaining under hazardous criteria led to no other areas being depicted. Behind this system, there is a low-confidence potential for a system that could affect at least the Panhandle around Sunday-Monday but there is a better signal for stronger development reaching into the North Pacific/Aleutians/Alaska Peninsula next Monday-Tuesday. This latter system would bring another episode of strong winds and enhanced precipitation. Expect a warmer trend over most of the state during the period, bringing moderately below normal readings as of Friday to or above normal and increasing the positive anomalies elsewhere. In most cases the anomalies for daytime highs should be greater than for morning lows. Central/southern parts of the Panhandle may remain below normal into the weekend. 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