Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 711 PM EDT Wed Aug 18 2021 Valid 12Z Sun Aug 22 2021 - 12Z Thu Aug 26 2021 ...Heavy rainfall possible across portions of southern Alaska and the Panhandle... ...Overview and Guidance Evaluation... An amplified pattern will take shape over Alaska during the extended range period. An initial closed low lifting into the Bering Sea by Sunday should slowly drift eastward into the Mainland Monday-Tuesday. This should send a frontal system across the southern Coast towards the Panhandle region Sunday-Tuesday. Behind this, another shortwave dropping into the Bering/central Aleutians by mid-week next week will help to maintain broad extended troughing over Alaska through day 8. To the north, a compact closed upper low will slide just north of the state, driving a cold front and additional troughing into the northern half of the region. The latest 12z cycle of models and ensembles show good synoptic agreement on the overall pattern through the period. There is good enough agreement in the deterministic solutions to warrant a general model blend between the 12z GFS, ECMWF, and CMC for days 4-5. After that, uncertainty remains high in the details of individual systems and shortwaves rotating through the base of the trough into the Aleutians. The 00z ECMWF/ECENS solutions showed some timing inconsistencies with the rest of the guidance, but the 12z runs came in much closer to the consensus. As such, the WPC progs for days 6-8 used an increasing weighting of the ensemble means to help mitigate some of the differences. Did maintain some degree of deterministic solutions just to help maintain system definition later in the period. ...Weather/Threats Highlights... The system expected to track into the southern-southeastern Bering Sea and the Mainland should bring wet and unsettled weather across much of southern Alaska and into the Panhandle. Southerly flow ahead of the attendant cold front in the Gulf will direct significant moisture into southern Alaska to fuel moderate to heavy rainfall initially for parts of the Peninsula region on Sunday, steadily shifting eastward with time across the southern coast and into parts of the Panhandle Monday-Tuesday. Rainfall should wane across western portions of this area after the weekend, but could linger a few extra days across southeast Alaska and the Panhandle as week troughing hangs out into mid-week. Some of the highest elevations across southern Alaska may also see measurable snowfall. Gusty winds are also possible along coastal locations as the system moves through and eventually weakens as the cold front moves into western North America. Some precipitation may also accompany the cold front dropping into the North Slope region on Sunday, but with lighter totals. The forecast continues to show below normal high temperatures over much of the state through the period but with some daily variability with system progression. Anomalies are likely to be the most below normal across the North Slope region behind the arctic boundary and linger into early next week. Overnight lows should be more moderate with various areas of above/below normal readings. Best potential for above normal lows will be over southern and eastern parts of Alaska. Santorelli Hazards: - Heavy rain across portions of mainland Alaska, Sun, Aug 22. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Aug 23-Aug 24. 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