Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 PM EST Sun Jan 28 2018 Valid 12Z Thu Feb 01 2018 - 12Z Mon Feb 05 2018 Guidance appears to remain within a lengthy process of settling on the details of important features during the extended period. The greatest disparity still involves the relative evolution of an eastern Siberia upper high and eastern Pacific ridge whose northern periphery should extend into the Gulf of Alaska for most of the period. While models have stabilized over the past day or so with respect to the idea of upper low energy tracking along/near the Aleutians during the latter half of the week, there are still significant question marks over specifics of this feature and energy within a larger scale central Pacific trough--along with corresponding surface features. Broadly speaking, over recent days and into today the ensemble means have been providing the most stable and similar forecast, keeping upper high and East Pacific ridge emphasis evenly balanced. This includes keeping the eastern Siberia upper high just west of the northern mainland while keeping the weakness between the upper high and eastern Pacific ridge close to the southern coast of the mainland. GFS tendencies have been either to weaken the upper high more quickly/progress it east/southeast, or less frequently retrograde it. Either way leads to greater emphasis on the East Pacific ridge. On the other hand sporadic ECMWF runs have tended to place greater emphasis on the upper high leading to a more suppressed pattern than the means. Among 00z/06z model runs, the 00z GFS/UKMET/CMC show greater east/southeast progression and weakening of the upper high while the 06z GFS/00z ECMWF maintain an upper high closer to the ensemble means. However the latter two models still diverge for flow southeast of the upper high. There is reasonable agreement/continuity in principle that the mean upper low over the Aleutians/North Pacific should retrograde and become part of an elongated mean trough as eastern Asia energy emerges over the western Pacific. Models and ensembles still differ widely for specifics of individual surface systems. One or more waves should be embedded within easterly flow while later in the period there is a general model/ensemble signal that energy aloft rounding the eastern Pacific upper ridge may lift low pressure or at least a wavy front toward/into the Gulf of Alaska. Guidance still expects a period of enhanced wind/moisture directed at the eastern Aleutians/Alaska Peninsula but with disagreement for timing/duration corresponding to surface low spread. For most of the period, trends/continuity have generally downplayed the northern side of surface low spread that extends into the Bering Sea. Some ensemble members show such a northern track for one or more lows but few enough for the means to remain along/south of the Aleutians. A blend consisting mostly of mostly 00z-06z operational models for day 4 Thu yielded a forecast closest to the 00z ECMWF mean in principle. By mid-late period the blend transitioned to 00z GEFS/ECMWF mean emphasis (06 GEFS mean not comparing quite as well to preference for some features) with lingering minority input from the 06z GFS/00z ECMWF, given preference to stay closest to the means and those two model runs being the closest to the means over the highest proportion of the full forecast domain. Rausch