Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 709 PM EDT Thu Aug 26 2021 Valid 12Z Mon Aug 30 2021 - 12Z Fri Sep 03 2021 ...Heavy rainfall possible for portions of the southern Coast region during the middle part of next week... ...Pattern Overview and Model Guidance... A large scale upper trough will progress eastward across the Aleutians into the Gulf of Alaska next week as an upper low settles across the Bering Sea. A couple of shortwaves moving through the base of the trough should send a couple of surface low pressure systems across the Aleutians into the Alaska Peninsula/southern Coast. Meanwhile, upper level ridging should build across the mainland Alaska the first half of next week before slowly shifting east as lower heights move into western Alaska. 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. Models and ensembles continue to show fairly good agreement on the synoptic pattern through much of next week, with typical uncertainties regarding the timing and details of individual systems later in the period. A general model compromise worked well as a starting point for days 4-5, leaning more towards the ensemble means days 6-8 to help mitigate the smaller scale differences. Minor contributions from the ECMWF/GFS were continued through day 8 though, just to add some definition to the washed out means. This approach maintained reasonable continuity with yesterdays WPC forecast as well as the forecast downstream across western North America. ...Sensible Weather... Much of mainland Alaska should be dry to start next week with the exception of some light showers along a frontal boundary draped across northern Alaska. The main weather maker will be a low pressure system approaching the Alaska Peninsula, lifting into the eastern Bering Sea, as it's attendant cold front drifts eastward through the Gulf. This will bring the potential for moderate to heavy rainfall and gusty winds from the Peninsula to the southern Coast. Models indicate 2 to 3 inches of rain is possible, especially for the southern coastal parts of the upper Peninsula, Kodiak Island, Kenai, and the Cook Inlet Thursday into Friday. Heavy rainfall may also extend eastward into far southeast Alaska and parts of the Panhandle next Friday and the weekend. Temperatures across the northern and central parts of Alaska should begin below to well below normal on Monday, before a warming trend kicks in the rest of the week. By Friday, much of the state could be near or above normal underneath of amplified upper level ridging. Santorelli Hazards: - Heavy rain across portions of mainland Alaska, Thu, 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