Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 633 PM EDT Wed Jun 03 2020 Valid 12Z Sun Jun 07 2020 - 12Z Thu Jun 11 2020 ...Overview and Guidance/Predictability Assessment... Today's guidance maintains good continuity for the general large-scale evolution during the period. The two primary features of note will be the upper low initially near the Alaska Peninsula and forecast to track across the Northeast Pacific--in the process interacting with a North Pacific surface low--and a western Pacific system that should affect the Aleutians during the latter half of the period. In the wake of a compact shortwave/upper low retrograding across the northeastern mainland early in the period, the upper pattern over the mainland and the Bering Sea becomes somewhat ill-defined but with a tendency toward ridging over the mainland and a weakness over the Bering Sea by next Tue-Thu. Within the agreeable and consistent mean pattern there are still some significant detail questions yet to be resolved for the initial upper low near the Peninsula and the surrounding flow. The slow/northward 12Z runs of the GFS and ECMWF both differed from their prior 6-/12-hourly runs and remaining model/ensemble mean consensus so preference was to split GFS/ECMWF input between the last two runs. For about the first half of the period the blend also included the 12Z CMC/UKMET, with the result providing a good intermediate starting point. Mid-late period inclusion of the 12Z GEFS/00Z ECMWF means increased from 20 to 50 percent with time. The operational model component maintained some 12Z/06Z GFS and 12Z/00Z ECMWF input through day 8 Thu and 12Z CMC input into day 7 Wed. The main trend of note is a moderate eastward adjustment for the upper low and associated northeastern Pacific surface low. Consensus continues to suggest the surface system should not track farther north than 50-55N latitude. Meanwhile the model/mean clustering for the system reaching near the Aleutians late in the period has been fairly good over the past day, providing better than average confidence relative to the forecast time frame. The aforementioned model/mean blend provided a good representation of this system through next Thu. Thermal lows/troughs will continue to dominate the surface pattern over the mainland. ...Weather Highlights and Hazards/Threats... Southern and central portions of the mainland should see periods of convection over favored terrain. The upper low initially over or near the Alaska Peninsula may enhance activity in its vicinity at least early in the period, with some uncertainty persisting over how quickly it will move into the northeastern Pacific. North Pacific low pressure will likely remain far enough south to keep its rainfall south of the mainland but some leading moisture could reach portions of the Panhandle. Expect the Aleutians to see rainfall and somewhat stronger winds by around midweek with the approach of western Pacific low pressure. Temperature anomalies will depend on location and elevation. The best potential for below normal highs will be over the south/southeast including the Panhandle while above normal highs will be more likely over the west and north. A greater percentage of the state should see above normal lows. 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 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