Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 654 PM EDT Sun May 23 2021 Valid 12Z Thu May 27 2021 - 12Z Mon May 31 2021 ...Overview and model guidance... The overall pattern across Alaska for the medium range will feature a large scale upper level low that will slowly move over or just south of the Aleutians the first half of the period, getting blocked and meandering near the eastern Aleutians by next weekend as upper level ridging amplifies over the mainland. Troughing may try to briefly move through northern/northeast Alaska late this week before shifting into northwest Canada by the end of the period. Guidance continues to show good agreement on the large scale pattern, but increasing uncertainty in the details towards the end of the period. The 12z ECMWF shifted its upper low position to closer match the GFS so the blend for the first half of the period favored a general model compromise. After day 5, the CMC seemed too eager to bring a closed low across northern Alaska and into the western Bering Sea where it then becomes the main upper low as the Aleutians low weakens. The ECMWF also supports energy drifting westward across Alaska, but weakens it late in the period keeping emphasis on the southern low. The ensembles also support maintaining a decent low across the Aleutians through the entire period, so after day 5 the CMC was excluded from the blend. The forecast for today favored a majority ensemble mean blend by day 8, with some inclusion of the GFS/ECMWF for added detail/definition. Overall, this approach seems to fit well with previous WPC continuity. ...Weather/Threats Highlights... The low pressure center and associated frontal system into the Aleutians should bring a period of unsettled weather to areas from the Aleutians to the southern mainland Coast. Fronts and embedded waves may provide some localized enhancement of precipitation and winds at times, but nothing seems particularly heavy or hazardous at this time. The best signal for highest totals during the five-day period exists from the eastern Aleutians to the Kenai Peninsula/Prince William Sound, with totals during that period of an inch or more. For temperatures, the Panhandle and southern coastal regions should remain at least modestly below normal through the entire period. North Slope to northeast Alaska may be much below normal to begin the period, but should moderate back towards normal (or slightly below) by the weekend. Much of western Alaska will remain near or above normal as upper level ridging holds in place aloft over these areas. Santorelli 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