Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 615 PM EST Wed Dec 11 2024 Valid 12Z Sun Dec 15 2024 - 12Z Thu Dec 19 2024 ...Storm to hurricane force winds possible near the southern Bering Sea and the Aleutians into early next week... ...Overview/Guidance Evaluation/Preferences... A mid-upper level ridge now across mainland Alaska will weaken over the weekend as a trough between the Sea of Okhotsk/Bering Sea and the Gulf of Alaska team up with a westward retrograding system from northwest Canada into the Alaskan Interior that tucks underneath a closed upper ridge/high over the Arctic Ocean. Within the west-to-east elongated upper trough, the main deep layered low is expected to be most persistent from the Bering Sea westward. There is a growing guidance signal supporting deep closed upper low/surface storm development near the Aleutians late weekend into next week and this pattern will increasingly over time favor additional downstream low intrusion up into a highly unsettled Gulf of Alaska, with growing snowy impacts through a cooled Southeast Alaska by next midweek. Overall, prefer a composite of clustered guidance of the 12 UTC GFS/ECMWF to provide max detail valid Sunday/Monday. Opt to transition to best compatible guidance from the GEFS/ECMWF ensemble means amid quickly growing forecast spread and run to run continuity issues through longer time frames. WPC product continuity seems reasonably maintained in this manner. ...Weather/Hazards Highlights... A deep Arctic air mass and associated 1035 mb or so high will build into the Yukon and interior north/eastern Alaska on Sunday. Temperatures at the surface could drop as cold as 35 below, with colder wind chills possible in the windier gaps. Temperatures will not be quite so cold as to be an extreme event. Further, as the cold air from the high reaches the gaps in the Chugach and northern Panhandle, predominant southerly flow over the Gulf should mitigate the gap winds some. The Arctic air will be short-lived, already moderating by Tuesday as a large low over the Bering approaches mainland Alaska and draws warmer Pacific air across much of the state. High winds associated with this low are forecast over the Aleutians on Sunday and Monday, which will weaken but remain gusty as they move towards the Gulf of Alaska midweek. Heavy rain at the lower elevations and mountain snows are expected through Kodiak and the western Gulf of Alaska through the Kenai Peninsula as the low approaches on Monday and Tuesday. A secondary low developing east of the primary low will spread heavy precipitation into the southern Panhandle on Tuesday, which may spread north up the Panhandle into Wednesday. Wegman/Schichtel Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: The WPC Hazards Outline depicts thse threats. 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