Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 412 PM EDT Sun Aug 05 2018 Valid 12Z Thu Aug 09 2018 - 12Z Mon Aug 13 2018 To commence the period, a complex array of upper troughs are sprawled across the state. The system dropping southward out of the Chukchi Sea is the primary one of interest as there may be interactions with upstream height falls by the weekend. This region spanning the north-central Pacific westward remains a point of extreme contention given the existence of Typhoon Shanshan and neighboring tropical invests. As of the last advisory, the forecast through Day 4 most mimicked the 12Z/00Z UKMET and 00Z ECMWF solutions. Thereafter, the guidance jumped out ahead of the forecast points as uncertainty builds considerably during extratropical transition. To further complicate matters, other potential tropical development looms out in the western Pacific basin which could spin up additional areas of low pressure. The ultimate impact of these features is the marked increase in amplification across the Bering Sea by next weekend. While the operational guidance varies with evolution, the idea of a deep low inhabiting the Bering Sea seems quite likely. Unfortunately, while ensemble means would be the best course of action here, they also average out all the spatial low positions which creates an unrealistic forecast. Ultimately will need to stick to an ensemble-based approach beyond Day 5/Friday given so many unknowns in the equation. Went with an equal blend of the 00Z NAEFS/ECMWF ensemble means with the 20-mb strength differences being averaged out. Before then, utilized a minimal amount of the 12Z GFS/00Z ECMWF in conjunction with ensembles before the pattern completely breaks down. Regarding impacts, it should prove to be a wet period, especially across the southern half of the state given the parade of shortwaves and eventual resultant mid-level southwesterly flow regime. It remains to be seen how wet the period will be, but some fairly hefty rainfall totals are possible during the Day 6-8, August 11-13 period with a deep extratropical cyclone approaching. Additionally, it could be quite windy depending on how strong pressure gradients become. Details should reveal themselves sometime next week, but too much uncertainty looms in the meantime. Rubin-Oster WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html