Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 646 PM EDT Tue Apr 28 2020 Valid 12Z Sat May 02 2020 - 12Z Wed May 06 2020 ...Guidance/Predictability Assessment... Most of today's guidance is fairly similar in principle. Consensus for this weekend shows separate ridges aloft over eastern Siberia/northwestern mainland and western Canada while a weakness separates the two. By the first half of next week the operational models differ on evolution of the Siberia ridge but the ensemble means indicate that the two ridges should eventually merge. Models/means have come into better focus in showing Arctic flow to the north of the overall ridge bringing a front to around the northern coast of the mainland by Mon-Tue. Meanwhile expect a mean low to meander over the northeastern Pacific with one or more embedded centers. The northern periphery of this circulation may bring some precipitation to the Panhandle as well as the southern coast and Peninsula. To the west a short-range Aleutians system should become a part of the Northeast Pacific mean low and then a system crossing Kamchatka should reach the Bering Sea by around Tue. The forecast blend started with a compromise among 12Z operational models for this weekend to reflect consensus for significant features while resolving lingering detail differences. Individual model runs began to diverge more significantly for some specifics after Sun. This led to a transition toward the 06Z GFS from the 12Z run, using a mix of 12Z and older 00Z runs for ECMWF input, and increasing total weight of 12Z GEFS/00Z ECMWF means to 35-50 percent by days 7-8 Tue-Wed. The 12Z GFS broke off energy aloft and an associated surface system over the western Aleutians on day 6 Mon while the remaining upper low back toward Kamchatka did not really lead to much of a surface reflection until a western Pacific wave tracked northeastward into the western Aleutians by next Wed. Remaining guidance did not provide much support for the 12Z GFS scenario while the 06Z run compared better. ECMWF runs showed various detail differences with decreasing confidence in which run would be better at later valid times. In addition to the increasing clarity with the Arctic front, latest guidance has generally trended toward holding the eastern Siberia upper high in place for a longer period of time and with greater strength, before possibly lifting northeastward and merging with the Canada ridge. General trends have been slower for the system forecast to reach the Bering Sea early-mid week. ECMWF runs have varied some with the evolution/timing of this system but thus far have been much more consistent in principle than GFS runs which have been very erratic with western Pacific through Bering evolution in general. GEFS mean runs have trended northward to consensus over the past day. Over the northeastern Pacific the latest operational cluster is close to the ensemble means which have provided the most stable solution for initial low pressure expected to wobble back to the northwest during the weekend and early next week. Models/individual ensembles quickly diverge for this and other possible low centers after early Mon, leading to decreasing confidence in specifics during the latter half of the period. ...Weather/Threats Highlights... The circulation around Northeast Pacific low pressure should spread some precipitation across parts of the Panhandle and then the southern coast and possibly into the Alaska Peninsula. There may be some enhancement along and southwest of the Kenai Peninsula depending on the surface low track during the first half of next week. Lingering moisture from a short-range Aleutians system may keep some light precipitation over the islands during the weekend and then next week low pressure emerging into the Bering Sea and its leading frontal system may bring some moisture into the Aleutians. Temperatures should be fairly steady during the period with a mix of positive/negative anomalies depending on location, though with somewhat of a tendency toward below normal readings over the Panhandle and eastern mainland and above normal over the western mainland. 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 Hazards: No significant hazards are expected over Alaska during this forecast period. 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