Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 749 PM EDT Fri Aug 06 2021 Valid 12Z Tue Aug 10 2021 - 12Z Sat Aug 14 2021 ...Heavy rainfall expected for portions of southern Alaska next week... ...Overview and Guidance/Predictability Evaluation... A broad upper level trough is expected to be in place across much of the state and extending across much of the Bering Sea and the Aleutians through much of next week. An upper level ridge axis situated over British Columbia and the Pacific Northwest will tend to limit the eastward progress of the trough, resulting in rather unsettled weather across much of the southern third of the state. This will especially hold true from the Kenai Peninsula to the southeast Panhandle region. Meanwhile, a closed low over the Arctic will likely send a cold front southward across the North Slope and Brooks Range, and a storm system over the North Pacific may begin affecting the Aleutians by next weekend. On the synoptic scale, the deterministic guidance is in relatively good agreement through the middle of the week. By Thursday and into Friday, the CMC is indicating more upper level ridging building in across the Aleutians, whilst the ensemble means are more supportive of a trough over this region. By the end of the forecast period, considerable model spread is evident with shortwave perturbations crossing the North Pacific. The WPC fronts/pressures forecast was primarily derived from a 12Z GFS/ECMWF/GEFS and 00Z ECENS blend, along with some previous WPC continuity, and then more of the EC and GEFS means for the end of next week and next Saturday. ...Weather/Threats Highlights... The upper level troughing over the state will tend to keep temperatures below early August averages across most of the state next week. These anomalies will likely be even greater for the Brooks Range and points northward with the arctic front moving through in response to the closed low north of the Arctic Coast. In terms of precipitation, multiple rounds of heavy rain are expected from the Alaska Peninsula to the southeast panhandle region as strong southwesterly flow at the low and mid levels advect copious moisture towards the coast at a nearly perpendicular angle. This could result in some locations potentially getting 3 to 6+ inches of rainfall across topographically favored areas as a couple of atmospheric river events are appearing increasingly likely. This will likely lead to some instances of flooding and enhanced run-off. Hamrick Hazards: - Heavy rain across portions of the Alaska Panhandle and south-central mainland Alaska, Mon-Fri, Aug 9-Aug 13. 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