Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 706 PM EDT Thu Aug 19 2021 Valid 12Z Mon Aug 23 2021 - 12Z Fri Aug 27 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 will slide along the Southern Coast Monday-Wednesday before the main trough shifts into Western North America late week. This should send a frontal system and plenty of moisture across the Gulf into the Panhandle region during the first half of next week. The next system moves behind this will move into south of the Aleutians by next Wednesday and reach the Gulf by Friday. To the north, a compact closed upper low will slide just north of the state early week while another shortwave sends a low pressure system into the northern Mainland region later in the week. The latest 12z cycle of models and ensembles show good enough agreement early in the week to warrant a general model compromise. After Tuesday, the uncertainty remains high in the details, especially regarding the late week system moving south of the Aleutians into the Gulf. There are both timing and strength differences in the models with this system. The ensemble means are in better agreement on the overall synoptic pattern, but as usual, don't maintain the details and tend to wash out systems. As such the WPC progs for days 6-8 quickly trend towards the ensemble means, with small contributions of the deterministic GFS and ECMWF just to help maintain some of that system definition. ...Weather/Threats Highlights... The amplified pattern expected next week should maintain wet and unsettled conditions across much of Alaska. Southerly flow ahead of the first cold front moving across the Gulf early week will continue to direct significant moisture into southern Alaska fueling moderate to heavy rainfall from parts of the southern Coast to Panhandle the first half of next week. General troughing ahead of the next system moving into the Gulf by next Thursday will maintain the heavy rain threat through much of the week for parts of southeast Alaska and especially the Panhandle. Some of the highest elevations across southern Alaska may also see measurable snowfall. A couple of shortwaves interacting with an arctic frontal boundary should allow lighter precipitation to fall across parts of northern Alaska as well early in the week. A stronger low pressure system should enter northwest Alaska next Thursday bringing increased chances for organized rainfall next Thursday into Friday. Moderate to heavy precipitation is possible. The pattern will continue to support below normal high temperatures over much of the state through next week, with the highest anomalies likely across the North Slope region. The overnight lows should be more moderate with the best potential for above normal lows over southern and eastern parts of Alaska. Santorelli Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Aug 23-Aug 24. - Heavy rain across portions of mainland Alaska, Sun-Mon, Aug 22-Aug 23. 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