Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 703 PM EDT Mon Jul 27 2020 Valid 12Z Fri Jul 31 2020 - 12Z Tue Aug 04 2020 ...Overview and Guidance Evaluation... The most uncertain part of today's forecast appears to be the evolution of energy to the west and south of an upper ridge expected to build over the mainland and western Canada. In varying ways the GFS/ECMWF/UKMET still take a decent proportion of initial eastern Bering Sea upper low energy into the northeastern Pacific/Gulf of Alaska. However they are generally slower to do this than seen 24 hours ago. The ensemble means had been hinting at trending in the operational model direction but now they have reverted to earlier runs that tracked most of the eastern Bering low directly to the north. The 12Z CMC does this as well. What happens with this feature and surrounding flow has an impact on northward ejection of the initial upper low over the eastern Pacific (near 50N 140W early Fri). One positive aspect of the forecast even with these combined uncertainties is that most guidance shows an upper low reaching or evolving over the Northeast Pacific/Gulf in some fashion, followed by ejection across or south of the Panhandle. Over the past day most guidance has been much more consistent and agreeable with the fairly strong system expected to track across the Bering Sea during the weekend into early next week. The most notable difference is that the 12Z/06Z GFS runs are faster than the model/mean consensus, favoring the 00Z run for the GFS component of the forecast. By later in the period a model/mean compromise looks reasonable to resolve latitude differences, with operational runs generally near or south of the ensemble means (which are all very similar). In order to yield a more modest adjustment from continuity between the eastern Bering and Northeast Pacific given the high sensitivity/low predictability for specifics, the first half of the forecast used a blend of the 12Z/00Z cycles of both the ECMWF and GFS along with a little 12Z UKMET input. Then the latter half of the period featured an even blend of models (both ECMWF runs and 00Z GFS) and means (12Z GEFS/00Z ECens). ...Weather Highlights/Threats... Some focused precipitation should persist into late week over the southwest mainland/Alaska Peninsula with the low pressure and wavy front associated with the upper low initially over the eastern Bering Sea. The ultimate path of this upper low is quite uncertain. Current forecast that pulls the low southeast would keep moisture confined to the southwest but a northward track (only modestly less than even probability) would extend organized precip farther northward over the western mainland. Then by this weekend Northeast Pacific/Gulf upper low evolution from one or more sources may bring a surge of moisture into the southern mainland/Panhandle with significant precip totals possible at some locations depending on specifics of flow aloft. A portion of this moisture may continue northward with time. A front settling near the central mainland could help to focus some activity as well. The fairly vigorous system tracking across the Bering Sea during the weekend into next week will likely bring a period of precipitation and stronger winds, with effects reaching the mainland late weekend/early next week. Best potential for highest totals with this system will be near the southern coast but other locations may see meaningful precip as well. From late this week into the weekend expect below normal high temperatures across the northern and southern thirds of the mainland along with the Panhandle, while warmer readings versus normal will prevail over the central mainland. With time the negative anomalies should expand and yield below normal highs over most of the state by next Mon-Tue, but still with greatest negative anomalies over the far north and south. Clouds/precip should promote broader coverage of above normal min temps. The North Slope may still see below normal lows though. 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 Hazards: - Heavy rain across portions of mainland Alaska, Thu, Jul 30. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Aug 1-Aug 2. 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