Alaska Extended Forecast Discussion National Weather Service College Park MD 709 PM EDT Tue Jun 3 2025 Valid 12Z Sat 07 Jun 2025 - 12Z Wed 11 Jun 2025 ...Overview... The extended range period begins Saturday with a persistent upper-low over mainland Alaska that will linger through the weekend before drifting southward early next week. To the South, an upper-level low and accompanying surface frontal system will lift northeastward from the northeastern Pacific and into the Gulf of Alaska. Both lingering precipitation chances from the initial upper-low and the approach of the next system will keep unsettled weather in the forecast at least through the weekend, with a general downward trend in precipitation expected as the Gulf system begins to weaken early next week. The presence of the persistent upper-low over the state will keep mean troughing in place and a period of generally below average temperatures. ...Guidance Evaluation/Preferences... Guidance has come into even better agreement with regards to the overall synoptic pattern this weekend. A persistent, lingering upper-low over the mainland looks to remain in place as another upper-low/accompanying surface frontal system over the northeastern Pacific lifts northward. The GFS, which was faster with this system the prior few days, is now in line with the ECMWF and CMC, and all guidance shows the system trending a bit stronger. This will likely bring greater heavy rainfall impacts to portions of the southern coast/Southeast. Thereafter, guidance begins to diverge a bit, but tends to favor two general features. First, the persistent upper-low over the mainland looks to continue, first drifting south over the southwest/southern coast before shifting eastward towards the Southeast. There are differences in the progression of this feature between the deterministic models, but all favor this general evolution. The means are less detailed, but at least the ECens and CMC ensemble show persistence of mean troughing shifting eastward with time. The surface reflection is more complex, with the latest 12Z ECMWF showing the potential for restrengthening and/or redevelopment of low pressure over the Gulf following the departure of the prior system. This would have the potential for increased precipitation chances along the southern coast. Most other guidance maintains a broad, strong area of high pressure over the Gulf and into the southern Coast. The second feature is the approach of another system upstream over the Bering Sea. The GFS remains faster with the approach of the system, but all deterministic guidance has come into better agreement on the general progression of an area of low pressure upstream of ridging in place to the east. The deterministic guidance is a bit faster than the means, which tend to hold the system back further to the west, and most guidance tends to agree that the ridging to the east will persist while the system begins to weaken. Regardless, there does appear to be a stronger signal for at least some modest precipitation chances over the Aleutians with the focused moist southerly flow between the low pressure system and ridge. Given the overall good agreement on the pattern and features, the updated WPC forecast used a composite blend of the ECMWF/CMC/GFS early to mid-period, with a contribution from the means later in the period as differences naturally increase, which captures the noted features without any strong preference in location/timing given to any one model. The most notable trends in the updated forecast are a stronger depiction of the Gulf system this weekend, potential for at least lingering if not increasing precipitation chances for these same regions mid-next week with the persistence of the upper-low, and increasing precipitation chances across the Aleutians with the approach of the system over the Bering Sea. ...Weather/Hazards Highlights... Precipitation chances will continue into the weekend and into early next week broadly across the mainland as a lingering upper- low remains in place. A threat for some heavier, potentially impactful snow over the Brooks Range given the cold temperatures in place may linger into Friday and early Saturday. A more concentrated area of heavier rainfall is expected along the southern coast and into the Southeast this weekend as another upper-low/accompanying surface frontal system lifts from the northeastern Pacific into the Gulf bringing a fetch of Pacific moisture. Forecast rainfall amounts have continued to trend upward, now in the 2-6" range, especially from Cordova southeast past Yakutat and into northern portions of the Southeast Saturday and possibly into Sunday. Some gusty winds are also expected, particularly for favorable gap locations. Shower chances will linger into early next week but with lighter amounts forecast as the upper-low shifts southward. An increase in precipitation chances may return to the southern coast/Southeast depending on the evolution of this system. An upper-level shortwave over the Arctic may also bring some increased precipitation chances to northwestern areas. Further west, a slow moving system shifting into the Bering Sea will likely bring some rainfall chances to the Aleutians early next week with some locally heavier amounts possible. High temperatures across much of the state will remain below average through the weekend and into early next week as mean troughing remains in place in the upper levels. Most of the state will see highs 5-10 degrees below average, with even greater anomalies along the North Slope of 15-25 degrees. Forecast high temperatures are generally in the 30s for the North Slope, 40s and 50s for western interior/coast and Aleutians, 50s for the Southeast, and 50s to mid-60s for the central/eastern interior and Southcentral. While temperatures will remain cooler and below average, there does look to be a slow but steady warm up through the period, with temperatures rising a degree or two each day, particularly for the interior. Putnam 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