Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 650 PM EDT Fri Aug 21 2020 Valid 12Z Tue Aug 25 2020 - 12Z Sat Aug 29 2020 ...Overview and Guidance Evaluation/Preferences... The primary focus of the forecast continues to be on two dominant features. The first is an upper low/associated trough tracking from the Bering Sea through the Gulf of Alaska/Northeast Pacific, currently expected to cross the Panhandle around late Thu-early Fri. A surface low of moderate strength and trailing front will accompany the upper dynamics. Farther west there is still a decent signal for low pressure development between the North Pacific and Bering Sea in association with consolidating energy that originates from eastern Asia. However models/ensemble members continue to show a lot of spread for exactly how the system will evolve. Also of note, leading energy aloft will support an early-period wave over the Gulf of Alaska and a system behind the North Pacific/Bering feature may begin to affect the western Aleutians by day 8 Sat. The 12Z ECMWF/GFS/UKMET represent the majority cluster for initial Gulf low pressure and the system that tracks east-southeast from the Bering Sea, with reasonable support from the ensemble means. The CMC strays to the slow/deep side of the spread, as has been its tendency over the past day or so. The non-CMC consensus has trended a bit slower over the past 12-24 hours though. Guidance spread has not really improved for North Pacific into Bering Sea evolution. ECMWF/ECMWF mean runs have been consistent in showing fairly early and strong consolidation of upper dynamics, leading to a deep Aleutians/Bering Sea system. The 00Z ECMWF may have been too deep with some 500mb height anomalies reaching at least four standard deviations below normal. The new 12Z run is less extreme. 06Z/12Z GFS runs take longer to develop and ultimately bring a more suppressed North Pacific wave into the far eastern Bering as it deepens while the GEFS mean is slower and quite weak. The 12Z CMC tracks southeast of the GFS after Fri. For another alternative, the CMC mean holds low pressure back over the western Aleutians. With low confidence today's preference is to emphasize a solution closest to the ECMWF/ECMWF mean--providing better continuity than other options. The main adjustment is a moderate southward trend around day 6 Thu. ECMWF/CMC runs, some GFS runs, and the 12Z CMC mean all indicate a late-period system that may reach the far northwestern Pacific and possibly affect the western Aleutians by day 8 Sat. The 06Z GFS was much more comparable to the majority cluster's western Pacific pattern than the 12Z run late in the period. Combining preferences for features of interest, the starting blend used the 12Z ECMWF/GFS/UKMET/CMC (ordered from most to least weight) early in the period and then transitioned to mostly 12Z ECMWF/00Z ECMWF mean emphasis, while minority GFS input switched from the 12Z run to 06Z run around mid-period. ...Weather Highlights/Threats... The combination of a leading Gulf of Alaska wave and trailing system tracking east-southeast from the Bering Sea will favor highest precipitation totals along the southern coast and Panhandle, while other portions of the mainland also see episodes of precip with varying intensity. Expect a drier trend from west to east late next week. From Thu into next weekend an area of enhanced precipitation and stronger winds should spread across parts of the Aleutians/Bering Sea and eventually into the western mainland with developing North Pacific-Bering Sea low pressure. Continued significant spread for exact system evolution keeps confidence fairly low for determining the coverage, timing, and intensity of sensible weather effects. Below normal high temperatures will be most likely over the southern mainland and Panhandle for most of the period. Other areas should vary between above or below normal highs depending on location/elevation. Meanwhile a large percentage of the state should see above normal lows. Expect the warmest anomalies to be over the northern mainland. There may be a few pockets of slightly below normal min temps over central/southern areas. 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