Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Wed Oct 06 2021 Valid 12Z Sun Oct 10 2021 - 12Z Thu Oct 14 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 is forecast to track into the Bering Sea into southwest Alaska Sunday into Monday, then form a triple point low deepening in the Gulf of Alaska around Tuesday. Then Tuesday into Thursday, another low should move across the Bering Sea and possibly across or near the Aleutians, leading to additional low pressure in the Gulf. Areas of enhanced precipitation and/or strong winds are likely with each system. ...Guidance/Predictability Assessment... Model guidance is in reasonably good agreement compared to typical, but with somewhat more model spread than yesterday's forecast. There were minor timing and amplitude differences initially with the mid-upper shortwave coming into the Bering Sea Sunday into Monday, with GFS runs a bit weaker/slower, the 12Z ECMWF/CMC a bit stronger and faster, and the 12Z UKMET sort of a compromise with a slower but deeper solution. Overall a blend of the 12Z deterministic guidance worked well for the beginning of the forecast period to average out these differences. The low pressure system trended faster compared to the previous forecast per the latest guidance. By around Tuesday, less guidance is showing a mid-upper low closing off temporarily in the Gulf of Alaska compared to yesterday's agreeable guidance showing such; the 12Z ECMWF is the main model still doing so. So there is lower confidence with a trough or closed low given the day-to-day model variability. This also has implications for the strength of the surface low--generally weaker than yesterday's forecast, and WPC trended this direction. The 12Z CMC does appear to be a southern outlier with the surface low and it was excluded from the blend after the beginning of the period. The next low pressure system has fairly good agreement that it should track into the Bering Sea Tuesday, but there are timing and track differences as it moves east (north, over, or south of the Aleutians), but will likely reinforce low pressure in the Gulf by Thursday. By the latter part of the forecast period, used a 50/50 blend of deterministic GFS/EC and the GEFS and EC ensemble means. ...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 spread 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. Temperatures should generally be cooler than normal through the period 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 through the first part of next week. Low temperatures are expected to generally be 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, Sat, Oct 9 and 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, Sat, Oct 9. 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