Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 721 PM EDT Thu May 30 2024 Valid 12Z Mon Jun 03 2024 - 12Z Fri Jun 07 2024 ...Overview... A closed upper low south of the Alaska Peninsula to start the period on Monday will move into the Gulf Tuesday-Wednesday. This should support a modestly deep surface system in the Gulf of Alaska and a period of heavy precipitation across Southeast Alaska and the interior mountains. Meanwhile, an upper low in the Arctic looks to send at least some energy southward into the Bering Sea where there is some support for a modestly deep upper low by late period, while several weaker shortwaves traverse the southern side of this mean troughing south of the Aleutians and towards the Gulf. Over the Mainland itself, upper ridging should build. ...Guidance Evaluation and Preferences... The latest guidance shows pretty good agreement in both placement and strength of the upper low and resulting surface system over the Gulf Monday to Wednesday, as well as southward progressing energy from the Arctic through the Bering Strait. By mid-week though, uncertainty increases substantially with regards to how much energy dives southward from the Arctic low and how strong/dominant it becomes over the Bering Sea. The latest 12z runs of the ECMWF and the GFS both suggest a stronger upper low reflection over the Bering Sea by next Thursday, with the Gulf energy/low eventually becoming wrapped up into it. The CMC however keeps the stronger upper low north over the Arctic with a stronger system well south of the Aleutians and upper ridge over the Bering creating a more blocky pattern. The GFS and ECMWF are by far the strongest with an upper low over the Bering but the AI/ML models and ensemble means do generally suggest more late period troughing over the Bering than the CMC does. The WPC forecast was able to use a blend of the deterministic models for the first half of the period amidst good model agreement. Began increasing weighting of the ensemble means late in the period to help smooth out the harder to resolve details. For this most part, this maintained good continuity with the yesterdays WPC forecast as well, through day 7. ...Weather/Hazards Highlights... The deep upper low and surface system over the Gulf early next week should bring a period of moderate to heavy precipitation to much of the Southeast/Panhandle and into parts of the interior mountains. Several inches of rainfall is possible, especially along the coast, during this multi-day period. Showers are also possible farther inland and north/west associated with upper level energy dropping down the West Coast. Expect temperatures to be below to well below normal across much of the Southern half of the Mainland most of the period, as well as the North Slope region (trending warmer by late week). The beginning of the week should be warmer than average across the eastern Interior region but may trend cooler/back towards normal later in the week. Santorelli 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