Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 650 PM EDT Thu Aug 20 2020 Valid 12Z Mon Aug 24 2020 - 12Z Fri Aug 28 2020 ...Overview and Guidance Evaluation/Preferences... Most guidance is fairly similar in depicting southeastward elongation of initial upper trough/low energy over eastern Siberia and the Bering Sea with the core of the energy ultimately tracking across the Gulf of Alaska and possibly into western Canada by late in the week, followed by upstream energy leading to a potentially stronger Aleutians/Bering Sea feature after midweek. A delay in 12Z ECMWF output prevented that run from being examined/used in today's forecast. A blend of the 12Z GFS/CMC/UKMET and 00Z ECMWF provided a reasonable starting point for days 4-5 Mon-Tue, reflecting a modest triple point wave that develops near the southern coast of the mainland. By mid-late week the models/ensembles diverge for timing of energy that reaches the Gulf of Alaska region and the system reaching the Aleutians/Bering Sea, with additional question marks for other details of this latter evolution. Timing differences essentially fall into two clusters. The faster consists of GFS/ECMWF/ECMWF mean runs and the slower includes the CMC/CMC mean/GEFS mean (plus the UKMET by the end of its run). At least through the 00Z cycle the ECMWF mean has been the most consistent piece of guidance, and with deeper low pressure than other means, while the overall progression of flow appears to provide a little more support to the faster cluster. However the slower option is well within the realm of plausibility and typical error range several days out in time so some account for that scenario is reasonable. Thus the early-period operational blend trended to a model/mean solution that included 40/30 weights of the 12Z GEFS/00Z ECens but enough lingering 12Z GFS/00Z ECMWF input to tilt the end result a bit to the faster side. The 12Z ECMWF/ECMWF mean generally maintain support for the progressive cluster, while the ECMWF mean has adjusted south for the Aleutians system--a nod to some operational runs. ...Weather Highlights/Threats... The upper trough/embedded low(s) elongating from Siberia and the Bering Sea into the Gulf of Alaska, along with possible low pressure, should support organized areas of precipitation over portions of the mainland and Peninsula/Panhandle--especially in the Mon-Wed time frame. Continued progression of the upper dynamics would promote a drier trend later in the week. Best potential for highest precipitation totals will be near the southern coast and Panhandle. By the latter half of the week the system forecast to reach the Aleutians/Bering Sea will be accompanied by an area of enhanced precipitation and stronger winds. Some effects from this system could reach the western mainland next Fri if the faster half of the spectrum verifies. The south-southeast and Panhandle should see mostly below normal highs through next week. Northern areas will likely see above normal highs on Mon followed by a cooling trend to near or slightly below normal readings, though some warmer pockets may persist. Elsewhere expect a mix of above or below normal readings depending on location/elevation. For min temperatures above normal anomalies will prevail with only some scattered areas of near to below normal readings. 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