Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 723 PM EDT Sun Apr 18 2021 Valid 12Z Thu Apr 22 2021 - 12Z Mon Apr 26 2021 ...Overview and Guidance/Uncertainty Assessment... Latest guidance continues to depict a fairly blocky regime during much of the extended range period, with upper ridging/high pressure dominating much of mainland Alaska. To begin the period on Thursday, the guidance agrees an upper low/surface low should settle into a position just south of the eastern Aleutians/Peninsula region, but weaken as the main low shifts north/west into the Bering and energy rounding the base of the trough drives the cold front through the north Pacific into the weekend. By Sunday, another upper low should approach the Aleutians and move eastward with time, with the associated organized surface cyclone drifting near or just south of the Aleutians. Generally speaking, the models show fairly good agreement on the overall large scale pattern as depicted above, but diverge greatly on the details as well as timing of various systems, especially past about day 5. The GFS continues to be the model most consistent in holding onto the blocky pattern across the region, while the ECMWF has shown more run to run variability on how quickly to break down the ridge. The ensemble means also support the GFS in holding onto the mainland ridge, so a preference towards stronger ridging is preferred at this time. The WPC forecast for days 4-5 uses a mostly deterministic model blend (between the 12z GFS/ECMWF/CMC), increasing contributions from the ensemble means thereafter to account for the increased uncertainty with timing and details of the deterministics. Did continue to carry roughly a third of the GFS/ECMWF combined into day 8 though just for some added definition to the otherwise fairly washed out means. This approach fits well with yesterdays WPC continuity as well as the preference downstream over the CONUS. ...Weather/Hazards Highlights... Most of Alaska should remain warm and dry through the period, with any precipitation confined to the Aleutians/Alaska Peninsula and vicinity associated with the couple of surface cyclones, first on Thursday, and then again next weekend. Mainly light to moderate amounts are expected, though some locally higher totals could be possible depending on exact strength and track of systems. Each system may also bring a period of gusty winds to parts of the region as well. The vast majority of the state should be well above normal in terms of temperatures through much of the period, with the warmest anomalies over the North Slope region and western areas of the Mainland (with even more anomalous warm morning lows). Lowering heights across Alaska next weekend should help to moderate temperatures a bit, especially for eastern areas. The exception to all this warmth will be in the southeast quadrant and much of the Panhandle where temperatures should be near or below normal the entire medium range period. 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 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