Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 641 PM EDT Sat Sep 19 2020 Valid 12Z Wed Sep 23 2020 - 12Z Sun Sep 27 2020 ...Overview and Guidance/Predictability Assessment... A deep upper low in the Gulf of Alaska to begin the period (Wednesday) should weaken as it shifts eastward into Western Canada. Meanwhile, another upper low crosses the Bering Strait by mid-late next week, establishing over the Bering Sea and eventually the eastern Aleutians by next weekend. Several shortwaves rotating underneath the Bering Sea low will eventually send another storm system south of the Aleutian island chain into the Gulf again to end the period. There is decent agreement in the models on the overall large scale pattern, but significant differences in the details, especially in regards to timing/intensity of shortwaves across/south of the Aleutians and into the Gulf. For days 4-5, the WPC forecast relied on a majority deterministic model blend between the agreeable 12z GFS/ECMWF. After day 5, leaned increasingly heavier on the ensemble means (00z ECENS/12z GEFS) to mitigate the detail uncertainties. ...Weather/Threats Highlights... The initial surface low in the Gulf will continue to bring heavy precipitation and gusty winds across parts of southern Mainland and the Panhandle through mid-week. Showers should linger through the period across the Aleutians into the mainland within an otherwise unsettled pattern and as the next system enters the Gulf next weekend. Much of the southern coastal areas and the North Slope will have maximum daily temperatures near or below average through the extended period while much of the Interior will observe above average temperatures underneath of upper ridging. Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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