Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 659 PM EST Fri Nov 15 2024 Valid 12Z Tue Nov 19 2024 - 12Z Sat Nov 23 2024 ...High winds and heavy snow could create blizzard conditions across parts of northwestern Alaska through the middle of next week... ...Overview... Clear and cold conditions across much of mainland Alaska early next week will give way to moderating temperatures and increasingly stormy weather for western and northwestern Alaska heading into midweek as an increasingly amplified pattern develops. The cold upper low lingering northeast of Alaska early next week will give way to a strong ridge building into the Aleutians/Bering Sea. This will be followed by the arrival of an amplifying trough from Siberia, from which a cyclone is forecast to develop and move through the top edge of the amplifying ridge. The gradient between the strong ridge and the digging Siberian trough will bring a long fetch of moist southerly flow across the Bering Sea, bringing an increasing threat of high winds and areas of heavy snow into the northwestern mainland beginning Tuesday and through midweek. Meanwhile, a cyclone passing south of the Aleutians is forecast to become more robust and expansive with time as it tracks east near/along 50N latitude. It appears that much of the impactful precipitation associated with this system will pass south of the Panhandle through midweek next week. ...Guidance Evaluation/Preferences... Model guidance especially the ensemble means today continue to show excellent agreement on depicting an amplifying upper-level ridge to propagate eastward across the Bering Sea early next week. Meanwhile upstream from the ridge, guidance also shows an upper-level trough located across eastern Siberia will begin to dig east towards the amplifying ridge. This is when the model solutions begin to diverge. Since 12Z yesterday, the ECMWF has settled with a solution that allows a cyclone to develop and move northeast into the Arctic Ocean through the top edge of the amplifying upper ridge through midweek next week. The Canadian model (CMC) did forecast a similar solution since a couple of days ago although the cyclone center tracked much farther north with time. The latest CMC runs had adjusted the cyclone track farther south to agree much better with the ECMWF solutions since then. The 12Z GFS solution, however, strays farther and farther away from the ECMWF/CMC solutions with time, and thus is considered an outlier. The 06Z GFS solution agrees much better with the ECMWF/CMC cluster. Similar model discrepancies were noted not only regarding the system that is forecast to impact northwestern Alaska but also across other parts of the Alaska domain. The faster eastward progression and development of the aforementioned cyclone mean that the high winds and areas of heavy snow are expected to reach western and northwestern Alaska earlier than the previous forecasts. In addition to the earlier arrival of the high winds and heavy snow, a high wind area has been included for the North Slope where very blustery conditions are forecast to prevail behind the departing cyclone. The WPC forecast package was based on 40% from the 12Z ECMWF and 00Z EC mean, 40% from the 06Z GFS and 12 GEFS, as well as 20% from the 12Z CMC and CMC mean. This blend yielded a solution with the Siberian cyclone pushing farther east into western and northwestern Alaska early to middle next week than the previous WPC forecast package. ...Weather/Hazards Highlights... Much of mainland Alaska will begin with rather cold conditions early next week under clear skies. Meanwhile, a strong high pressure system is forecast to build east across the Aleutians. The tight pressure gradient between the high and a retreating low over the Gulf of Alaska can lead to gap wind enhancements across the eastern Aleutians and into the southern Peninsula. More impactful weather in terms of increasing east to southeasterly winds and development of moderate to heavy snow are then forecast to reach northwestern Alaska by Tuesday ahead of a warm front. The combination of the heavy snow and high winds would create blizzard conditions. If the associated cyclone moves faster than forecast, the heavy snow across Seward Peninsula could taper off on Wednesday. The snow and winds will likely penetrate farther east across the Brooks Range and the North Slope on Wednesday, with high winds possibly linger across the North Slope into Thursday behind the departing cyclone. It appears that the high winds and snow will gradually taper off towards the end of next week. The cold conditions across much of the Alaskan domain early next week will likely persist into Wednesday morning for the eastern Interior but much milder temperatures are expected to be ushered into western Alaska by Tuesday along with the high winds and heavy snow. The North Slope is forecast to be much milder than normal under west to southwesterly flow while the eastern and southern section including the Panhandle will be colder than normal for late next week. Kong 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