Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EDT Wed Jul 25 2018 Valid 12Z Sun Jul 29 2018 - 12Z Thu Aug 02 2018 Models initially showed good agreement with respect to the synoptic scale pattern across Alaska during the extended period. Strong consensus exists for a deep upper low and associated surface cyclone across the southern Bering Sea on day 4 (Sun), with downstream ridging in place from western Canada into eastern/southeastern Alaska. As a result, a majority deterministic multi-model blend (including the ECMWF/GFS/CMC/UKMET) served as a good basis for the forecast starting on day 4. This continued to be the case through days 5-6 (Mon-Tue) as the Bering low pressure system moves northward and gradually weakens, while the front moves east toward the Alaska Peninsula. Model spread increased modestly during days 5-6, and weighting of ensemble means (ECENS/NAEFS) was gradually increased as a result. This scenario will result in widespread showers for the Alaska Peninsula and the west coast of mainland Alaska during days 4-6. By days 7-8 (Wed-Thu) spread began to more rapidly increase among the deterministic guidance, with relatively poor run-to-run continuity as well, in some cases. Significant areas of uncertainty by this time period are the degree of potential amplification in the upper ridge across the north Pacific, the persistence of the trough/upper low from mainland Alaska into the northern Gulf, and potential interaction of this feature with additional shortwave energy arriving from eastern Asia (and possibly even from the Arctic). As a result, the ECENS/NAEFS means were given majority weighting in the forecast for days 7-8. Despite the variety of solutions, the most significant forecast uncertainty is across the Aleutians where the amplitude of the aforementioned north Pacific ridge will play a significant role in the eventual outcome. A persistence of unsettled conditions across mainland Alaska seems to be a common theme among most solutions despite the variability. In addition to the wet conditions, temperatures will be above average across much of the state through the extended period due to the combination of upper ridging and southerly flow ahead of the incoming trough. Ryan 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