Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 318 PM EDT Thu May 31 2018 Valid 12Z Mon Jun 04 2018 - 12Z Fri Jun 08 2018 Upper flow continues to look quite blocked across Alaska (and much of the northern hemisphere) through the medium range. This results in a flow pattern that will be relatively slowly evolving, but also rather chaotic, with low predictability at the smaller scales. An upper ridge is expected to persist across eastern Asia into next week, and downstream of the ridge, negative height anomalies are expected to persist (in the form of an upper low) across the Bering Sea and the Aleutians, perhaps working east toward the Gulf of Alaska by the middle of next week. Meanwhile, upper ridging will initially be dominant from eastern Alaska/northwestern Canada north to the Arctic Ocean. Models/ensembles show some degree of weakening of this feature during the forecast period, although it remains a bit unclear to what degree this will occur. Model consensus is relatively good early in the period. The 00Z ECMWF/UKMET were most the solutions most tightly clustered with the consensus with respect to the deep low initially across the Bering Sea and the shortwave/triple point low traversing just south of the Gulf of Alaska. A blend of these solutions served as a good forecast starting point for days 4-5 (Mon-Tue). From Wed (day 6) onward, model solutions begin to diverge and forecast confidence decreases. One major point of contention is whether the upper low quickly moves east into the Gulf of Alaska (00Z CMC), or progresses more slowly (00Z ECMWF), nearing the Alaska Peninsula by late next week. Deterministic solutions have varied significantly from run to run - while ensemble means support something either in the middle or toward the slower side. Meanwhile, disagreement also emerges as to whether a ridge axis will be able to expand into interior Alaska, and whether shortwave energy of Arctic origin will be able to move southward into Alaska. Analysis of teleconnections based on anomalous Rex Block over Asia seem to support at least some degree of ridging over the interior, but also support keeping the negative height anomaly center closer to the Alaska Peninsula and not too far east into the Gulf. Given these considerations and the uncertainty, the forecast for days 6-8 was based on a majority blend of the 00Z ECENS/NAEFS means, with a continued minority component of the 00Z ECMWF. In terms of sensible weather, the medium range will initially be unsettled with frequent showers and gusty conditions across the Aleutians and the Alaska Peninsula. Higher probabilities for precipitation should gradually migrate eastward ahead of the upper low, with southern mainland Alaska and Southeast Alaska seeing increasing for precipitation from Tue night onward. Ryan WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html