Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 558 PM EST Sat Jan 23 2021 Valid 12Z Wed Jan 27 2021 - 12Z Sun Jan 31 2021 ...Major Bering Sea Storm to Threaten Alaska and the Gulf of Alaska mid-later next week... ...Overview and Guidance/Uncertainty Assessment... Quite an active storm track on tap with a powerhouse closed low/trough and ~950 mb surface low slated to reach the Aleutians and Bering Sea into Wednesday that will slowly fill while spinning over the Bering toward western Alaska Thursday into Friday. This system already has a well defined mid-latitude satellite signature off eastern Asia and offers a substantial maritime threat. Ample downstream energy transfers over the AKPen/Southwest AK/Kodiak Island and into the Gulf of Alaska offer subsequent well organized maritime low re-development. Guidance flow evolutions have trended in much better agreement, bolstering forecast confidence quite a bit. Accordingly, the WPC Alaskan medium range product suite was derived from a well clustered blend of the 12 UTC GFS/ECMWF/Canadian models days 4-6 (Wednesday-Friday) along with the 19 UTC National Blend of Models. Added the GEFS/ECMWF ensemble means to the composite blend days 7-8 for max WPC product continuity through next weekend in an amplified pattern with above normal predictability. ...Weather/Hazards Highlights... The deep Bering Sea storm will spread heavy wrapping precipitation and a threat of high winds/waves to the Bering Sea and into the Aleutians midweek, and an enhanced snow risk into western/southwest Alaska Thursday into Friday with approach. Amplified upper ridging building over the Interior/North Slope in advance of the deep low will meanwhile weaken, slated to reform back over the Bering Sea next weekend. Forecast spread increases in Arctic stream flow rounding the ridge, but the WPC guidance blend allows a decent venue for impulse energy to dig into a cooling/unsettled Interior in increasing amplitude flow. Underneath, downstream transition across the AKPen/Kodiac Island will result in a pattern favorable for deepened northern to eastern Gulf of Alaskan low developments later week into next weekend, but recent guidance trends do show a slightly more offshore track from the Southeast Panhandle. WPC PoPs guidance and associated parameters have decreased accordingly from yesterday as per coordination with WFO Juneau. However, the well organized low should remain a maritime threat into next weekend. Schichtel 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