Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 544 PM EDT Sat Jul 17 2021 Valid 12Z Wed Jul 21 2021 - 12Z Sun Jul 25 2021 ...Overview... No change in thinking here. It is still the case that there is strong guidance signal indicating that the current blocky pattern will start to break down and move east next week, but with continued/renewed troughing into an unsettled Bering Sea/Strait then western/northwestern Alaska. Meanwhile, ample undercutting storm energies will increasingly work through the Aleutians/Southwest/AKpen to the Gulf of Alaska. A lead upper low initially south of Haida Gwaii will very slowly move into British Columbia as weakening ridging over the Interior/Southcentral moves into the Yukon as the pattern relaxes. ...Guidance/Predictability Evaluation... Same as yesterday. The WPC Alaskan medium range product suite was primarily derived from a blend of well clustered guidance of the 12 UTC GFS/ECMWF and GEFS/ECMWF ensemble means along with the 19 UTC National Blend of Models days 4-8. Predictability seems to stay above normal through the period, albeit with a gradual increase in forecast spread with time as addressed by minority weighted inclusion of the ensemble means. WPC continuity is well maintained, in part again due to subsequent manual adjustments to this WPC blend to ensure offshore low depth consistent with favorable upper support and lowered uncertainty in this pattern. ...Weather/Threats Highlights... It remains the case that precipitation will be focused, especially into midweek, over western/northwestern Alaskan areas during the period under southwest flow with Bering lows approach/height falls, as well as across the Aleutians along the tail-end of the frontal boundaries. Widespread tenth to a quarter inch with focused half to one inch rainfall (locally more) is possible over these areas over a 1-2 day period with each system. Some precipitation will also overspread the North Slope/Brooks Range with inland system translation and weakening. Meanwhile, ample undercutting energy flow through the Southwest/AKpen and into the Gulf of Alaska will lead to deepening northern Gulf low and frontal system genesis. While the details of embedded systems in this flow is not well established in guidance that offers less than stellar run to run continuity upstream, this emerging pattern will offer unsettled maritime conditions over the Gulf and periods of locally enhanced rainfall into southern and southeastern coastal areas mid-later next week. Schichtel 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