Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 525 PM EDT Sat Sep 26 2020 Valid 12Z Wed Sep 30 2020 - 12Z Sun Oct 04 2020 ...Overview and Guidance/Predictability Assessment... Model/ensemble guidance is agreeable and consistent in showing a very amplified upper pattern during the medium range, featuring a strengthening ridge over western Canada and a mean trough (with a couple of embedded lows) over and extending well south from the western mainland. Upstream, a high amplitude ridge over northeast Russia means there is confidence the closed low centered south of AK over the north Pacific will be slow to move through next weekend. Guidance suggests above average confidence in the first cyclone moving north across the upper Aleutians/AK peninsula on Wed into the southeast Bering Sea/coastal southwest AK Thu morning. This means a forecasts consisting of a blend of the ECMWF/GFS/UKMET should work to mitigate minor timing/intensity differences. There is more spread for the following Fri-Sat cyclone, as the GFS/ECMWF/Canadian models continue to have run to run changes plus differences with each other. Consequently, the forecast gave low weight to the 06-12z GFS and 00-12z ECMWF, as well as the respective GEFS Mean and ECMWF Ensemble Mean. The multi-model/multi-ensemble blend was needed, given significant run to run changes in the GFS and ECMWF, which means low confidence in any one model run yet until models start to converge and have improved continuity. ...Weather/Threats Highlights... The pattern evolution will favor increasing potential for heavy precipitation from the AK Peninsula to the northern Panhandle. The first surface low tracking northward towards Kodiak Island, should advect moisture into the Gulf of Alaska and eventually the southern Coast/northern Panhandle early next week, with gale force winds likely to accompany the cyclone. The next system will probably bring another round of moderate to heavy rainfall late next week into next weekend, but the timing and intensity details remain in question. The strength of the lows in the ECMWF, GFS, Canadian, and German ICON favor another surge of high winds and heavy rain for Kodiak Island to the southern coastal areas, including areas from the Kenai peninsula east to the northern panhandle. If this storm materializes at the end of next week, a flooding threat will develop as well, so this system is well worth monitoring. Expect widespread coverage of above normal lows prevailing across much of the Alaska mainland. The one area of below normal temperatures is near the upper trough in the lower Aleutians. Petersen 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 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