Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 233 PM EST Sat Jan 12 2019 Valid 12Z Wed Jan 16 2019 - 12Z Sun Jan 20 2019 Latest guidance is starting to show a more coherent signal toward an upper high closing off within the northern part of the overall area of mean ridging expected across northwestern North America into the Arctic. Exact high position from day to day as well as evolution of shortwave energy that may track to the south of the upper high continue to have a fairly high degree of uncertainty though. Meanwhile there is still a lot of guidance spread for specifics within an axis of mean troughing aloft/associated surface low pressure center(s) from the Bering Sea into the northern and eastern Pacific. Aside from low confidence in the details, the overall pattern still favors a period of enhanced moisture flow directed to some areas from the Alaska Peninsula to Kenai Peninsula into late week. Farther west there is good agreement/continuity in principle for a broad upper trough with embedded upper low to move into the western half of the Pacific. By next weekend the height falls ahead of this western Pacific trough should ultimately push away energy within the initial Bering Sea/northern-eastern Pacific mean trough, yielding a general east-west axis of cyclonic flow aloft over the North Pacific/Aleutians into Gulf of Alaska by next Sunday. For the first half of the period the 06Z-12Z GFS and 00Z ECMWF/CMC provided the best relative agreement for depicting somewhat enhanced detail over the ensemble means. GFS runs have been inconsistent with the position of the upper high over/north of the mainland but the 06Z-12Z runs have adjusted toward recent ECMWF/CMC runs that have showed an upper high path near or north of the northern coast of the mainland. Teleconnections relative to the associated positive height anomaly center in recent D+8 charts have favored leaning more in this direction versus the 00Z and some earlier GFS runs that had been farther south with the upper high. At the same time the aforementioned model cluster suggests some interaction of southeastward-tracking Bering Sea energy and northwestward-moving North Pacific energy/low pressure that would track close to if not across the Alaska Peninsula. Enough models show this feature to favor more definition than the ensemble means but this system is still very uncertain given the spread of individual ensemble members. The rest of the period incorporated increasing weight of 06Z GEFS/00Z ECMWF ensemble means while lowering input of the operational guidance given additional detail spread in the guidance. Current majority scenario has the upper high lingering near the northern coast of the mainland with some possible retrogression beginning around day 8 Sun. The 12Z GFS was dropped from the blend late in the period due to bringing the upper high eastward instead--though it did build another upper high into Siberia. Developing low pressure over the eastern Pacific late in the week may track far enough northward to have some influence on the Gulf of Alaska region by next weekend but with only a fairly weak signal in the means by day 8 Sun. Consensus remains good with a frontal zone nearing the western Aleutians late this week, followed by ongoing detail uncertainty regarding embedded wave development. Thus far the ensemble means have been consistent in keeping the overall surface trough axis south of the Aleutians through next weekend while models/individual ensemble members are quite varied for latitude. This favors leaning closer to the means for the time being. Rausch 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 http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html