Alaska Extended Forecast Discussion National Weather Service College Park MD 659 PM EDT Mon Jun 30 2025 Valid 12Z Fri 04 Jul 2025 - 12Z Tue 08 Jul 2025 ...General Overview... The upper pattern will be characterized by a stable upper level high over the North Slope/Brooks Range later this week and into/through the weekend. To the south, at least a couple systems will traverse the Aleutians/Alaska Peninsula and into the Gulf, bringing enhanced rainfall chances to these regions as well as the southern coast. This pattern will be conducive to warm to hot temperatures and enhanced thunderstorm chances over the interior which may spark some fire concerns. ...Guidance Evaluation/Preferences... The 12Z model guidance suite was in relatively good agreement overall with the handling of the main upper features in a blocky pattern with an upper high over the northern interior/North Slope and a persistent upper low in the Aleutians to Alaska Peninsula vicinity. The largest differences were associated with the evolution of the upper low/individual waves/surface systems across the Bearing, Aleutians, and into the Gulf. The GFS/ECMWF/CMC were all well clustered through day 5 (Friday/Saturday) depicting an initial surface low pressure/frontal system over the Gulf weakening with eastward progression as ridging increased to the east, and a second surface low pressure/frontal system associated with an upper-low to the west crossing the Aleutians to Alaska Peninsula. Then, the GFS diverges from the ECMWF/CMC, and shows a second upper low developing upstream over the Bering Sea, with the two remaining separate features through the next couple of days as they both progress eastward. The ECMWF/CMC, as well as the ensemble means, show the initial upper low persisting as the main feature and remaining slow in eastward progression. The means tended to progress a bit faster, with the ECMWF and even moreso the CMC slower through late this weekend and into early next week. Additional shortwave energy looks to reinforce the low pressure/frontal system by early next week with some uncertainty in the exact evolution of the pattern. Regardless, the pattern supports rain chances for the Alaska Peninsula and southern Coast through at least this weekend, with more scattered chances into the interior, and additional rain chances westward through the Aleutians but with more uncertainty with the specifics given increasing smaller-scale differences. The updated WPC forecast used a composite blend of the GFS/ECMWF/CMC through day 5, with the ECens/GEFS means replacing the GFS for days 6-8 as the GFS diverges from the other solutions and uncertainty grows. ...Weather/Hazards Highlights... A blocky pattern with an upper high anchored over the central/northern interior and North Slope will promote warm to hot temperatures through this weekend and into early next week. Highs south of the Brooks range may reach the mid- to upper 80s, with 70s for the North Slope outside of coastal regions. Thunderstorm chances may increase by later in the week as anomalous easterly flow around the upper high increases instability when combined with very warm surface temperatures. Thunderstorms without much rainfall could lead to fires started by lightning, especially across the Tanana Valley as well as the Copper River Basin and Lower Kuskokwim delta region. To the south, the passage of at least a couple systems into the Gulf will bring wet weather to the Alaska Peninsula and southern coast. The rainfall looks to be heaviest for the Alaska Peninsula through the 4th, and then eastward along the southern coast including Kodiak Island and the Kenai Peninsula through at least the 5th. Rainfall chances, including heavier rainfall, may linger especially for the southern coast into early next week. An additional system upstream may also bring some rainfall, potentially heavy, to the Aleutians. In contrast to the north, highs here will remain cooler and below average with persistent cloud cover and showers, mostly in the 50s and 60s. The Southeast may see some precipitation chances depending on system evolution, but the region should be mostly drier than average throughout the period, with highs in the 50s and 60s here as well. 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