Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 702 PM EDT Mon Jul 26 2021 Valid 12Z Fri Jul 30 2021 - 12Z Tue Aug 03 2021 ...Heavy rainfall possible for parts of western and northwestern Alaska... ...Guidance/Predictability Evaluation... The medium range period over the Alaska region looks to feature a couple of shortwaves moving through the Bering Sea into far northern Alaska/the Arctic before a much deeper low becomes established over the Bering Sea by late weekend or early next week. Meanwhile, an upper low will drift only slowly westward through the period in the Gulf/Panhandle region while upper level ridging holds on across southern and eastern Alaska. The latest ensemble means remain reasonably compatible with each other on this pattern, while the deterministic GFS, ECMWF, and CMC show typical differences in the smaller scale, lower predictability, features. The WPC Alaska grids leaned more on the deterministic models days 4-6, with increasing contributions from the ECENS/GEFS means days 7-8. Favored the 12z GFS slightly more than the 12z ECMWF late period because it was more compatible with the means on placement of the Bering Sea low. ...Weather/Threats Highlights... The main areas of precipitation and unsettled weather will be focused across the western and northwestern mainland throughout the period as southerly flow ahead of the Bering Sea cyclone interacts with stalled frontal boundaries. A reinforcing trough from eastern Siberia could ingest moisture from T.S. Nepartak and is forecast to reinvigorate the Bering Sea low next weekend into early next week to sustain the general rainfall across western Alaska. Heavy rain is possible especially across the wind-facing upslope terrains of Lisburne and Seward Peninsulas where rainfall amounts may approach climatological extremes. Temperatures should remain below normal for western and northern parts of Alaska but they should trend warmer over eastern parts of the state as upper level ridging builds in aloft. 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 - Heavy rain across the southern portions of Lisburne and Seward Peninsulas in mainland Alaska, Thu-Mon, Jul 29-Aug 2. - Heavy rain across portions of southwestern Alaska, Sat-Mon, Jul 31-Aug 2. - Heavy rain across portions of southwestern Alaska, Fri-Mon, Jul 30-Aug 2. 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