Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 646 PM EST Thu Dec 3 2020 Valid 12Z Mon Dec 7 2020 - 12Z Fri Dec 11 2020 ***Major Gulf of Alaska storm early next week brings high winds and heavy precipitation*** ...Guidance and Uncertainty Assessment... The deterministic and ensemble guidance is in relatively good agreement on the strong Gulf low on Monday in terms of magnitude, with the 12Z ECMWF on the northern side of the guidance. More noteworthy differences appear by Tuesday with the 12Z CMC depicting another strong low lifting northeastward towards the Gulf region. However, this solution has very little support from the ensemble means and was not used in the forecast process. There is better model support for a low pressure system near the Aleutians by next Thursday, but the ECMWF is considerably farther to the northwest than the GFS. Given the uncertainty among the deterministic guidance for this time range, the forecast was based primarily from a GEFS/ECENS compromise for the Thursday to Friday time period. Some of the 12Z ECMWF and less of the GFS was used for early in the week along with the ensemble means. ...Weather/Hazards Highlights... An intense low pressure system over the northern Gulf of Alaska on Monday is forecast to gradually weaken by the middle of the week. This storm is expected to produce strong and gusty winds across the Aleutians and the southern mainland coast, along with additional heavy rain and mountain snow across areas that have already been hammered by relentless precipitation over recent days. This may result in additional episodes of flooding and shoreline erosion. Farther inland across the Interior and the North slope region, a generally benign weather pattern is expected, except for more modest early next week spillover moisture/snows into the Interior as the aforementioned deep low lifts northward and weakens over the Gulf toward southern Alaska. Additional surface lows upstream with lower predictability are subsequently slated from the northern Pacific towards the Aleutians and vicinity by the middle to end of the week. Hamrick Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Dec 6-Dec 7. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Dec 6-Dec 7. - High significant wave heights for coastal portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Dec 6-Dec 7. 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