Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 549 PM EST Sat Nov 13 2021 Valid 12Z Wed Nov 17 2021 - 12Z Sun Nov 21 2021 ...Much below normal temperatures likely across much of Alaska through the medium range period... ...Overview and Guidance Evaluation/Preferences... An upper level low, with troughing extending into the Gulf of Alaska, will be present over southern Mainland Alaska to start the period on Wednesday. The low should slowly retreat into Canada, though some form of weak troughing may linger across the state through next weekend. At the surface, a modestly deep cyclone will be present in the Gulf, but should gradually weaken through the period as the next system from the north east Pacific moves towards the region. To the West, another deep upper low will drop southward over/near the western Aleutians Thursday-Saturday, as multiple perturbations in the base of the trough send a couple of surface low pressure systems into the well south of the Aleutians, and eventually into the southern Gulf by next Sunday. For days 4-5/Wednesday-Thursday, the guidance shows reasonable enough agreement to allow a general deterministic model blend between the 12z GFS, ECMWF, and CMC. After this, differences and uncertainties in the details quickly begin to arise especially with respect to how much troughing gets left behind over the Mainland the last half of the period and also with the next upper low dropping into the western Aleutians and the shortwaves rounding the base of that trough. As is typical for these long range periods, the deterministic models get pretty chaotic south of the Aleutians, that a blend towards the better agreeable ensemble means seems to be the best approach to smooth out the harder to resolve details. Some modest amounts of the 12z ECMWF and CMC were maintained even through day 8, since those solutions are closest to the ensembles and should give some additional definition/depth to individual systems. This approach also maintains good continuity from yesterdays forecast. ...Weather/Hazard Highlights... Much of the precipitation over Alaska should be confined to the Aleutians/Southern Coast/Panhandle, with much of the mainland remaining very dry and cold, other than maybe a few snow showers. The low pressure system in the Gulf on Wednesday-Thursday will likely bring a period of moderate to locally heavy precipitation to much of the Panhandle region with wet conditions, but lighter in intensity, lingering the rest of the week associated with maintained weak troughing across the Gulf. In addition, favorable flow funneling through the mountain ranges of southern Alaska are likely to result in the potential for localized but strong outflow winds across downwind locations of southeast Alaska. Precipitation chances again increase by next weekend across the Panhandle as the next low pressure system approaches. A system into the Aleutians late next week should bring unsettled conditions to the region with light to moderate precipitation spreading towards the Peninsula and Southern Coast as well. Much below normal temperatures should prevail across much of Alaska (with the exception of the North Slope region) through next week as surface high pressure becomes established across much of the state. The most pronounced anomalies should be over the western to southern part of the state where daytime highs could be as much as 20-30+ degrees below normal. Temperatures should remain below normal into next weekend, but may moderate slightly as the upper trough weakens and upper ridging attempts to sneak in from the west. Santorelli 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