Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 748 PM EDT Wed Aug 07 2024 Valid 12Z Sun Aug 11 2024 - 12Z Thu Aug 15 2024 ...A quick round of wind-swept rain expected to move through the Aleutians into mainland Alaska this weekend with high-elevation snow across portions of the Alaska Range... ...Overview... The amplified synoptic pattern currently prevailing across the larger Alaskan domain will favor energetic upper-level troughs to periodically pass through the Bering Sea toward mainland Alaska through the medium-range period. These energetic troughs will then lift north to northeast across mainland Alaska ahead of an upper high that is forecast to remain anchored over northern Canada. One such disturbance will likely bring a quick round of wind and rain through the Aleutians into mainland Alaska this weekend before sliding across the southern coastline of Alaska early next week. The next system of concern is forecast to move from Siberia into the Aleutians/Bering Sea from early to middle of next week with varying forecast intensities depicted by global models today. ...Guidance Evaluation/Preferences... For the upcoming cyclone of interest, the 12Z ECMWF and 12Z CMC yesterday led the way with a faster forward motion of the system across the Bering Sea heading toward southwestern Alaska on Saturday. The GFS followed suit since yesterday. Today, models have generally trended toward developing a more compact system with a more concentrated punch of wind-swept rain pushing through southwestern Alaska later on Saturday into Sunday. Models have also trended faster in lifting the system northeastward across mainland Alaska as the system weakens from Sunday into Monday. The next system of interest appears to eject eastward from Kamchatka Peninsula into the Bering Sea by early next week. Model solutions today have generally shown more spread than yesterday regarding the track and intensity of this system. The 12Z ECMWF now indicates a rather robust cyclone moving into the Bering Sea/Aleutian domain by midweek next week while weaker cyclones/waves are shown by the GFS and CMC. The consensus of the ensemble means generally agree with a broad cyclone centered over the Bering Sea as another cyclone meanders over the Arctic Ocean by Day 8. These synoptic features are depicted on today's WPC prognostic charts for Days 7 and 8. Thus the WPC forecast blend used a multi model deterministic and ensemble mean solutions from the 12Z GFS/GEFS, 12Z ECMWF/00Z EC mean, and 12Z CMC/CMC mean, but leaning more toward the ensemble means by Day 5 onward. This blend yielded a solution reasonably compatible with yesterday's forecast package. ...Weather/Hazards Highlights... With the next energetic upper trough and relatively deep surface cyclone forecast to head toward the west coast of Alaska on Saturday, a quick round of wind-swept rain can be expected to impact the Aleutians and into mainland Alaska this weekend. The rain is expected to be moderate to locally heavy through the Aleutians with winds in excess of 40 knots at times. The wind and rain will then overspread much of western Alaska later on Saturday into Sunday where portions of southwestern Alaska is forecast to receive heavy rainfall in excess of 1.5 inches as depicted on the WPC Hazards map. Heavier rainfall amounts are expected to be farther downstream across portions of the terrain-favored locations of the southern coastline of Alaska. In addition, the higher elevations of the Alaska Range north of the Alaska Peninsula will be cold enough for the precipitation to fall as snow, where a few inches to a foot of accumulations are possible. The moisture associated with the weakened system will likely push through much of the rest of mainland Alaska through early next week with lighter amounts of rainfall and perhaps little to no rain across the North Slope. Meanwhile, the next system of interest is forecast to bring widespread rainfall from west to east across the Aleutians during the first half of next week. There is higher than normal model uncertainties with this system at the moment. This system will be watched for possible high wind threat across the Aleutians in future forecast updates. 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