Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 659 PM EDT Tue Aug 17 2021 Valid 12Z Sat Aug 21 2021 - 12Z Wed Aug 25 2021 ...Overview and Guidance Evaluation... The extended range period over Alaska region begins with a closed upper level low which should lift across the central/eastern Aleutians and into the southeast Bering Sea this weekend before opening up into broad troughing and slowly drifting east into the western Mainland next week. The latest suite of guidance shows good agreement on the large scale with this feature, but continues to struggle with individual perturbations through the base of the trough, particularly later in the period. Farther north, a compact closed upper low should slide just north of Alaska which likely drives a cold front into the Northern Slope region. Again, the models show good agreement early on, with diverging timing and strength solutions later on. Across the board, a general model blend between the 12z GFS, ECMWF, and CMC was used for days 4-5. After that, increased contributions from the ensemble means in order to mitigate some of the details. Continued some minor inclusion of the deterministic models just for some added definition to individual systems. This approach maintained reasonable continuity with yesterdays WPC forecast. ...Weather/Threats Highlights... The system expected to track across the Aleutians into the southern-southeastern Bering Sea and eventually the Mainland should bring wet and unsettled weather across much of the Alaska region. Organized rainfall is likely from the Aleutians and the Alaska Peninsula this weekend, extending into the mainland from late weekend into next week as low pressure continues eastward. Some of this moisture will likely extend into the mainland from late weekend into next week as low pressure continues eastward. There are still significant detail differences that affect the coverage and intensity of the precipitation at that time. Some areas of moderate to heavy totals are possible with the best signal currently along/near the southern coast into the Panhandle. Gusty winds are also likely along coastal locations from the Western Mainland, across the eastern Aleutians, the Peninsula, and into the Southern Coast. Meanwhile precipitation should accompany the cold front dropping into the northern mainland but with lighter totals. By the first part of next week there will be a question of how much moisture with the system to the south may interact with the front. The forecast continues to show below normal high temperatures over much of the state through the period but with some daily variability with system progression. Anomalies are likely to trend colder over northern areas during the latter half of the period behind the Arctic cold front. Lows should be more moderate with various areas of above/below normal readings. Best potential for above normal lows will be over some southern areas early and late in the period and over the North Slope on Saturday ahead of the Arctic front. Santorelli No significant hazards are expected over Alaska during this forecast period. 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