Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 800 PM EDT Fri Aug 27 2021 Valid 12Z Wed Sep 01 2021 - 12Z Sun Sep 05 2021 ...Heavy rainfall possible for portions of the southern Coast region during the middle part of next week... ...Pattern Overview and Model Guidance... During the extended period ridging will be in place over much of the interior and southeast and will shift eastward as a upper trough progresses across the Aleutians into the Gulf of Alaska. As this happens an upper low will begin to settle in over the Bering Sea and a series of short waves will pass through the base of the trough, spinning up a couple of surface fronts that will track across the Aleutian Chain and into southern coast/Alaska peninsula. Meanwhile, to the north, a strong polar vortex and associated mid-level westerly flow will be in place across the Arctic and North Slope early in the week before heights begin to rise again across the region and the Polar Vortex retreats to the north. In general, the latest model guidance and the ensemble means are maintaining a decent consensus with this synoptic pattern for the coming week. As usual, there is the typical uncertainties regarding the timing and details of individual systems later in the period. The 12Z GFS solution was a little fast than the 06Z run, but both were clustered well with the 12Z ECWMF and the ensemble means. For continuity purposes, continued to rely on a blend of the 12/6Z GFS/ECWMF through the whole period will increasing weighting of the ECENS, GEFS and NAEFS means through the mid and late periods. This helped reduce spread for southern and southeast portions of the state. ...Sensible Weather... Light showers may occur over northern Alaska near a draped frontal boundary early on which will keep temperatures below seasonal average across the northern and central parts of the state. High pressure will keep much of the interior and parts of the panhandle drier. By Friday, much of the state could have daily temperature near or above normal underneath of amplified upper-level ridging. Rain will steadily spread from the peninsula to the southern as a low pressure system lifts into the eastern Bearing Sea, as it's attendant cold front drifts eastward through the Gulf. Rain may be moderate to heavy at times, especially from upper portions of the peninsula, Kodiak Island, Kenai and the Cook Inlet into Friday. The heavier rain may reach in far southeast Alaska late Friday and through the weekend. Along with heavy rains, these areas may also experience gusty winds. Campbell Hazards: - Heavy rain across portions of southern Alaska, Wed-Thu, Sep 1-Sep 2. Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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