Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 622 PM EDT Thu Aug 5 2021 Valid 12Z Mon Aug 9 2021 - 12Z Fri Aug 13 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. An upper level ridge axis situated over British Columbia will tend to limit the eastward progress of the trough, resulting in rather unsettled weather across much of the southern third of the state, particularly 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. On the synoptic scale, the deterministic guidance is in relatively good agreement, but the 12Z UKMET begins to deviate across the Gulf with a more progressive solution with a shortwave emanating from the main upper trough axis. The 12Z CMC has come into better agreement regarding the placement of the arctic low and is similar in latitudinal placement with the ECMWF, while displaced from the more northern GFS solution. By the end of the forecast period, the CMC becomes a bit more amplified with the trough over the northern Gulf, but still within the realm of possibility. The WPC fronts/pressures forecast was primarily derived from a 12Z GFS/ECMWF/CMC blend, along with some previous WPC continuity, through Wednesday, and then more of the EC and GEFS means for the end of next week. ...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 moderate to heavy rain are expected from the Alaska Peninsula to the southeast panhandle region, with some locations potentially getting 2 to 4 inches of rainfall across topographically favored areas. This may lead to some instances of flooding and enhanced run-off. There may even be some snow showers for the northern third of the state, especially for the Brooks Range. Hamrick Hazards: - Heavy rain across portions of the Alaska Panhandle and south-central mainland Alaska, Sun-Thu, Aug 8-Aug 12. - Heavy rain across portions of the Alaska Panhandle, Mon-Wed, Aug 9-Aug 11. 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