Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 708 PM EDT Sun Jul 25 2021 Valid 12Z Thu Jul 29 2021 - 12Z Mon Aug 02 2021 ...Guidance/Predictability Evaluation... The latest ensemble means from the ECMWF, GFS, and CMC remain reasonably compatible with each other through Day 8--basically keeping the Bering Sea low and the ridge across southern and eastern Alaska in place. Some erosion of the ridge is probable as there is general ensemble consensus for an upper trough to edge closer from the Gulf of Alaska next weekend and into Monday. The GFS has been the fastest with respect to bringing a developing cyclone into the Gulf of Alaska next weekend while the ECMWF and CMC have been slower. Meanwhile, the 12Z GFS appears to develop a spurious low pressure system south of the Aleutians. The 06Z GFS appears more reasonable in this regard. Therefore, a general compromise of the ensemble means together with the 12Z ECMWF, 06Z GFS, and 12Z CMC should work well as a starting point. The WPC Alaskan grids were based on an even blend of these models/ensembles with a smaller contribution from the CMC starting on Day 4. By Day 7, only 25% of the deterministic GFS/EC/CMC was used with the reminder portion from the ensemble means. ...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 stationary boundaries under persistence deep-layer southerly flow. 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 can also be expected especially across the wind-facing upslope terrains. 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. Kong 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