Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 735 PM EDT Thu Oct 07 2021 Valid 12Z Mon Oct 11 2021 - 12Z Fri Oct 15 2021 ...Active pattern continues with periods of gusty winds and precipitation across southern Alaska... ...Pattern Overview... Progressive and energetic flow aloft will lead to multiple surface low pressure systems affecting portions of Alaska through the period. A surface low in the Bering Sea near the southwestern mainland Monday is expected to form a triple point low in the Gulf of Alaska/northeast Pacific by Tuesday. Then Tuesday into Wednesday, another low should move across the Bering Sea and possibly cross into the Gulf over the Alaska Peninsula, and this low pressure in the Gulf is likely to linger through the end of the workweek. Areas of enhanced precipitation and/or strong winds are likely with each system. ...Guidance/Predictability Assessment... Model agreement was fairly good for the initial part of the forecast, and though there have been run-to-run differences, most model guidance currently shows a mid-upper low closing off temporarily in the Gulf of Alaska around Tuesday, which also has implications for a stronger triple point surface low. The main outlier was the 12Z CMC, which takes the main shortwave northward rather than eastward Monday into Tuesday, which is not supported by other guidance. Thus used a deterministic model blend of the 12Z GFS, ECMWF, and some UKMET for the early part of the period. The next system tracking quickly across the Bering Sea Tuesday and into the Gulf has fairly good agreement with the surface low between the GFS and ECMWF and their ensemble means, despite some timing and amplitude differences with shortwaves aloft. Thus the model blend for the latter part of the period was comprised of a deterministic GFS/EC and the GEFS and EC ensemble mean blend for the most part. But did observe that the 12Z ECMWF looked like an outlier with upper-level and surface lows near the Bering Strait around next Thursday into Friday, arising from model differences over Russia earlier on. Leaned away from that solution given the model consensus is for low amplitude ridging over the Bering by then. ...Weather/Hazard Highlights... The initial low pressure system in the Bering Sea will spread light to moderate precipitation to the Aleutians, Alaska Panhandle, and the southwestern mainland early in the week. Then with low development in the Gulf of Alaska, Southcentral Alaska can expect enhanced precipitation beginning Monday with some threat of heavy amounts. Gusty winds are also possible, but will depend on the exact strength and track of the surface low. The low will then cause potentially heavy precipitation into the Panhandle beginning Tuesday as it tracks eastward. Then the next low pressure system should spread precipitation and brisk winds to the Aleutians and the western mainland Tuesday into midweek, while persistent low pressure in the Gulf keeps the moist inflow into the Panhandle and thus precipitation chances there through late week. Temperatures should generally be cooler than normal through next week for much of the southern part of the mainland and the Panhandle, particularly in terms of highs. For the northern two-thirds of the state, near average highs are forecast with a mixture of slightly below and slightly above normal readings. Low temperatures are expected to be generally above normal for western and northern parts of Alaska. Tate Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Wed, Oct 11-Oct 13. - Heavy precipitation across portions of the Alaska Panhandle, Tue-Wed, Oct 12-Oct 13. - Heavy rain across portions of the Alaska Panhandle, Tue-Wed, Oct 12-Oct 13. - High winds across portions of mainland Alaska and the Aleutians, Sun-Tue, Oct 10-Oct 12. 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