Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 650 PM EDT Sat May 09 2020 Valid 12Z Wed May 13 2020 - 12Z Sun May 17 2020 ...Overview... The general pattern evolution over the forecast domain has maintained good continuity over the past day even if there is still significant uncertainty for some of the specifics. Guidance consensus shows a strong Arctic upper ridge, at times extending its reach into the mainland, gradually moving west with time. As this occurs expect a couple pushes of height falls from the northeast to support a trend toward cooler mainland temperatures with above normal readings becoming more confined to southern/western areas. Within the Pacific storm track, a leading system's influence on the Aleutians will wane after midweek as the surface low tracks into the northeastern Pacific (but remaining well south of the mainland) while the northern periphery of an emerging western Pacific system may affect the Aleutians next weekend or shortly thereafter. ...Guidance/Predictability Assessment... There is still a fair amount of spread regarding the first bundle of energy dropping around the eastern side of the Arctic ridge mid-late week. In the 12Z cycle the solutions ranged between the GFS that kept a fairly strong ridge over much of the mainland through Fri and CMC that brought a compact upper low across the southern mainland. Remaining guidance showed decent potential for at least some energy to retrograde underneath the Arctic ridge but with higher heights than the deeper side of the guidance--usually a reasonable way to lean given historical precedent in such an evolution. Recent ECMWF runs have been consistent in showing this retrogression though with the 12Z run trending weaker, while the GEFS mean has hinted at this weakness more than the 06Z/12Z GFS, adding support for the intermediate scenario. As the overall upper ridge continues westward, recent ensemble mean trends toward a stronger push of height falls from the northeast into the mainland next weekend provided support for partial inclusion of the stronger energy seen in operational runs--but with a blend approach to downplay uncertain specifics. Beyond the ensemble mean trends, consensus movement of the ridge on its own should lead to increasing potential for troughing to move into the mainland by next weekend. Most aspects of model/ensemble consensus have held up well over the Pacific. The system initially tracking away from the Aleutians has trended a bit faster from yesterday but the track has been fairly consistent. Clustering has improved somewhat for the western Pacific system that may begin to have some influence on the Aleutians next weekend. Recent trends have generally been a little farther south, leading to a modest delay for any effects reaching the Aleutians. Model/ensemble spread extends far enough south for minimal effects to be a possibility. Days 4-5 Wed-Thu started with a 12Z operational model blend followed by including a small component of 12Z GEFS/00Z ECMWF means by day 6 Fri. Days 7-8 Sat-Sun increased ensemble weight to 40-60 percent while keeping minority weights of the 12Z GFS/ECMWF plus added a little 00Z ECMWF to offset some localized lower confidence details in the new run. This blend yielded the desired intermediate solution and good continuity for the mainland later in the week, reflected trends for the stronger height falls heading in from the northeast next weekend, and toned down small-scale detail uncertainties with the Pacific systems. ...Weather/Hazard Highlights... The specifics are still somewhat in question but there is reasonable confidence in the general trend toward cooler temperatures over a majority of the mainland. Above normal readings should decrease in coverage and become more confined to southern/western areas while the pattern will gradually become more favorable for below normal temperatures over the north/east. Expect meaningful precipitation to be fairly limited in coverage during the period. The front settling into the southern mainland may focus some activity at times while light precipitation may reach northeastern areas next weekend with the arrival of upper troughing. The leading Pacific system may produce some lingering precip/wind over the Aleutians into Wed. As this system moves into northeastern Pacific expect its track to remain far enough south for at most a little moisture to reach the Alaska Peninsula/Panhandle. The system tracking over the western Pacific may bring some moisture into the Aleutians late in the weekend but with moderate to lower confidence. Rausch 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