Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 755 PM EDT Thu Jul 11 2024 Valid 12Z Mon Jul 15 2024 - 12Z Fri Jul 19 2024 ...Heavy Rainfall Threat across Southern Alaska this weekend... ...Overview and Guidance Evaluation/Preferences... The latest guidance solutions seem reasonably agreeable in depicting a slow-moving upper air pattern, with an initially deep cyclone centered near the west coast of mainland Alaska weakening and opening up with time toward the end of the medium-range forecast period. Deterministic solutions indicate that shortwaves will spin around the mean center of the cyclone at various speeds as the center of the cyclone drifts farther inland and de-amplifies over southwestern Alaska through next week. The ensemble means from the GEFS, ECMWF, and CMC show very good agreement in depicting the mean position of the weakening cyclone through Day 8. Therefore, the WPC forecast package today was based a blend of 40% from the 06Z/12Z GFS and 12Z GEFS, 40% from the 12Z ECMWF and EC mean, and 20% from the CMC/CMC mean for Days 3-5, increasing to more than 2/3 from the ensemble means by Day 8. This blend maintains reasonable WPC continuity. WPC manual edits were applied to better depict the strength of the main organized surface systems that seem to have the most favorable mean upper support as an offset to inherent smoothing from the blending process. ...Weather/Hazards Highlights... The southern portions of Alaska will be in the midst of a wet period as the medium-range period begins next Monday. The wettest day will probably be Sunday along the southern coastal areas and down through the Panhandle as depicted on the WPC Hazards Outlook map. Winds could reach gale force in the Bering Strait and on the back side of the surface cyclone across eastern Aleutians on Sunday. Cumulative heavy rain, 1-3" areal average amounts and local amounts in the 3-5" range are possible in the Panhandle. The heavy rain threat will generally decrease by midweek as the cyclone weakens but the rain can be expected to linger through late week with a period of enhanced rainfall possible in the Panhandle with the arrival of a low pressure wave. The remainder of the state will remain unsettled with scattered showers and perhaps some embedded thunderstorms. High temperatures will be more evenly distributed, with 60s and 70s in the central Valley, 40s on the North Slope, and 50s and 60s elsewhere. Subfreezing lows should be constrained to the higher terrain of the Brooks Range and the various ranges across south-central and southeast Alaska. The next round of rain should reach western Aleutians late next week ahead of the next low pressure wave. Kong/Roth 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