Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 500 PM EDT Wed Oct 02 2024 Valid 12Z Sun Oct 06 2024 - 12Z Thu Oct 10 2024 ...Dangerous Extratropical Storm associated with former West Pacific Typhoon Jebi to offer a High Wind/Wave Threat for the Bering Sea and Gulf of Alaska and a multi-day Heavy Precipitation and Runoff Threat into Southern and Southeast Alaska this weekend into next week... ...Overview and Guidance Evaluation/Preferences... Guidance continues to highlight development of a major storm with high winds/waves from the Bering Sea to the Gulf of Alaska and multi-day heavy precipitation and runoff threats for Southern to Southeast Alaska late week into next week. A deep extratropical low and moisture is associated with former West Pacific Typhoon Jebi. Prefer a composite of reasonably clustered guidance of the 12 UTC GFS/ECMWF/UKMET/Canadian this weekend and Monday. Pivoted to the 12 UTC GEFS ensemble mean later period amid growing forecast spread. The GEFS mean blends best with model trends. Manual adjustments will ensure sufficient system depth given closed upper trough support, tropical origins and to offset weakening inherent to a blending process. This forecast plan offers detail consistent with average to above normal predictability and WPC product continuity. The GEFS/ECMWF means are also more in line with a growing signal in support of another deepened low track across the Aleutians in about a week to monitor for strength and specifics. The 12 UTC GFS and ECMWF offer a deep system compared to the 12 UTC Canadian. Canadian ensembles offer some deeper low signal. ...Weather/Hazards Highlights... Eyes will be drawn to a large and deep storm system entering the Bering Sea region later in the week, with increasing rain chances along the West Coast and through the Aleutians into the weekend, and then through the southern tier of the mainland. Storm force winds and extremely rough seas are expected over the open waters of the Bering Sea and into the Gulf of Alaska, with strong winds likely across the Aleutians and into the AK Peninsula region as well, with gap wind enhancement. Heavy rainfall (and snow in the higher terrain) is possible across the southern Coast to Panhandle this coming weekend, with lingering inflow and focus into early-mid next week over moistened soils of Southeast Alaska terrain as guidance lingers the main low and redevelopments offshore over the unsettled Gulf of Alaska. In terms of temperatures, cooler than normal highs are likely over southern parts of Alaska and warmer than normal temperatures are likely for the northern two-thirds of the Mainland during the period, with an overall warming trend through the weekend owing to increased southerly flow ahead of the Bering Sea low pressure system followed by moderation. Schichtel 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