Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 702 PM EDT Fri Oct 15 2021 Valid 12Z Tue Oct 19 2021 - 12Z Sat Oct 23 2021 ...Stormy Pattern Continues from the Aleutians through Southern and Southeast Alaska... ... Guidance and Predictability Assessment... The extended range starts Tuesday with a low pressure system in the Gulf of Alaska and another one moving into the Bering Sea. Both systems should weaken by midweek as the next shortwave drops in across the Aleutians and into the Gulf. This in part may help to reinvigorate whatever might be left of T.S. Namtheun (currently in the West Pac) by that time, eventually resulting in a deep surface low (current guidance suggests upper 960s to low 970mb) well south of Alaska by Thursday/day 6. The latest 12z models actually show fairly good agreement on this pattern, so a general model compromise worked as a good starting point for the WPC progs days 4-6. After that, the models begin to diverge some with respect to timing and placement of this low as it slowly lifts northward towards the Panhandle/Gulf of Alaska. on bringing the low more north towards the Panhandle (ECMWF/CMC) or keeping it south (GFS). There is also timing/placement spread across the Bering Sea at the same time as another surface low tries to move across the eastern Aleutians/AK Pen region day 7-8. Given the time frame, the models actually show fairly good agreement on the large scale, but it's the details which remain in question. To help mitigate these late period differences, WPC trended towards the ensemble means days 7-8, along with smaller contributions from the 12z ECMWF and GFS. This approach allowed for good continuity from yesterdays forecast, as well as with downstream across the CONUS. ...Pattern Overview and Weather/Hazard Highlights... The mean low pressure pattern over the Aleutians and Gulf will keep cloudy/unsettled conditions through the extended period. Gusty winds with scattered to widespread precipitation (locally heavy) will continue into the early and middle part of next week across parts of the southern Coast and the Panhandle region ahead of the weakening initial low pressure system in the Gulf. Snow is also possible in the higher elevations of southern and southeast Alaska. At the same time, upstream flow should drive a deep storm into the Bering Sea by the start of the period with some light precipitation possible across far western mainland Alaska along with a period of stronger wind. This system should weaken as southern stream energy spins up a surface low south of the Aleutians into the Gulf and yet another deep system enters the western Bering/Aleutians. This likely brings another round of gusty winds and moderate precipitation to parts of the Aleutians Wed-Fri before the low departs into the Gulf and the pressure gradient weakens. The attendant cold front pushes eastward as we move into next weekend which should bring a round of enhanced and potentially heavy precipitation to parts of the Panhandle at the very end of the period. Temperatures from the Aleutians to the Panhandle should remain below normal through the period as a parade of storms moves through these regions. Into interior and northern Alaska, a warming trend is expected by the early to middle part of next week as upper level ridging tries to work over the state. Santorelli 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Thu, Oct 19-Oct 21. - Heavy precipitation across portions of the Alaska Panhandle, Fri, Oct 22. - High winds across portions of mainland Alaska, Tue, Oct 19. - High winds across portions of mainland Alaska and the Aleutians, Wed-Fri, Oct 20-Oct 22. 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