Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 533 PM EDT Tue Aug 13 2024 Valid 12Z Sat Aug 17 2024 - 12Z Wed Aug 21 2024 ***Multiple rounds of heavy rain and strong winds for portions of western Alaska through next Wednesday*** ...General Overview... An amplified and energetic upper level flow pattern across Alaska and the adjacent maritime regions will lead to multiple rounds of impactful weather for the state for the weekend and also into early-middle of next week. The initial low pressure system on Friday will likely be lifting northward across the Arctic Ocean as the next storm follows closely behind it for the weekend, with heavy rain and wind impacts expected for western portions of the state. After a brief break, the remnants of Typhoon Ampil may approach the region toward the end of the forecast period Wednesday. Upper level ridging over the Gulf will generally be anchored in place and thus keep weather conditions tranquil for southeastern portions of the state. ...Guidance Evaluation/Preferences... The 12Z guidance overall has trended stronger with the deep trough/closed upper low over the southern Bering Sea and the Aleutians for the beginning of the forecast period Saturday. However, the 12Z GFS was a weaker solution compared to its 6Z run, so the latter agreed better with the new 12Z model consensus, and thus the 6Z run was weighted more than the 12Z run. There are still timing differences as the storm system reaches western Alaska, with the UKMET faster and the CMC slower, and the GFS/ECMWF serving as a good middle ground compromise. Looking ahead to early next week, ensemble spread is greatest across the Bering Sea region and near the west coast of the mainland as the remnants of Typhoon Ampil enter this region by the Tuesday/Wednesday time period. The guidance agrees the most with the upper level ridge extending northward across the Gulf of Alaska and keeping the storm track away from the Southeast Panhandle region. The ensemble means were gradually increased to about 40% of the overall forecast blend by next Wednesday. ...Weather/Hazards Highlights... After a brief respite from the Friday storm, weather conditions are forecast to deteriorate again across the western mainland as a warm front lifts northward with an increase in rain and wind, ahead of the next strong low pressure system, followed by a another surge of wind as the cold front pivots through the region. Moderate to heavy rainfall is expected for portions of the Brooks Range, and extending south across the southwestern mainland and to the Alaska Peninsula as the main moisture plume moves through. Rainfall amounts could exceed an inch for some of these areas. Depending on how strong the surface low gets, winds could gust in excess of 50 mph at times across the terrain and also near the western coast. Looking ahead to next week, the third system (remnants of Typhoon Ampil) are expected to reach the Bering Sea region, and if the remnant low remains organized, another round of rain and wind could affect some of those same areas for Tuesday into Wednesday, including across the Aleutians. Stay tuned as future forecasts refine things further. Temperatures are generally expected to be slightly below average across the western half of the mainland through most of the period where the main storm track will be, and reinforcing cold frontal passages expected across this region. Warmer and slightly above average readings will likely be commonplace across the eastern mainland and extending to the southeast Panhandle region where the upper ridge axis will be governing the overall weather pattern. Hamrick 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