Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 757 PM EDT Mon Sep 20 2021 Valid 12Z Fri Sep 24 2021 - 12Z Tue Sep 28 2021 ...Significant Storms to Bring Heavy Precipitation to the Southeast Coast and Panhandle... ...Guidance and Predictability Assessment... The Alaska pattern in the medium range period will be generally characterized by an upper low drifting from the Arctic Circle southward to northwest of the state, while spokes of upper troughing pass across the state. At the surface, a series of potent low pressure systems are forecast to move across the Gulf of Alaska/northeast Pacific, causing the potential for strong winds and precipitation across the Aleutians to Southcentral to the Panhandle depending on the low tracks. Model guidance was generally agreeable with this overall pattern, but with differences in timing and depth of the features. On day 4/Friday, mid/upper heights/vorticity show some differences, with the 12Z ECMWF/UKMET swinging a vort max toward the Panhandle through a little faster compared to the 12Z GFS/CMC, with the EC and GEFS means generally in between. The WPC forecast leaned a little more to the quicker side but incorporated some GFS to show the potential for this movement. Then by the weekend, a deep surface low is expected to move likely south of the Aleutians and into the Gulf, which is generally agreed upon among the models, but the CMC is a weaker exception. There are also differences in the low track and how close it gets to the coast, which will create differences in the sensible weather for the southern parts of the state. For days 4-6, used a model blend of the GFS/ECMWF/UKMET along with the GEFS and EC means, which created a compromise position for the low. Then by early in the next workweek, there is some signal for another low strengthening in the Bering Sea as more upper-level energy drops southeast, but with variability in position among models and not a clear consensus. Used a blend of the GEFS and EC means for days 7-8 to minimize individual model differences, as the ensemble mean guidance was generally agreeable. ...Sensible Weather... The storm system first described above is forecast to cause significantly heavy totals of rain and higher elevation snow to areas from the far eastern Kenai Peninsula to the Panhandle for the latter part of the workweek, with 3-5 inches liquid possible in some areas. Then as the second strong low system tracks south of the state, another round of heavy precipitation is possible over the Aleutians depending on the low track, but likely across the Panhandle once again by early next week. Both storms could also produce a broad area of brisk to strong winds, but may stay offshore. Farther north, central/eastern parts of the mainland could see moisture and increased precipitation chances late this week, otherwise only light precipitation is forecast. The upper trough persisting over the mainland will keep temperatures below normal over much of the state. Coldest anomalies should be over the southwestern parts of the state and across higher elevations of the Brooks and Alaska Ranges. Tate Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Thu-Fri, Sep 23-Sep 24 and Sun-Mon, Sep 26-Sep 27. - High winds across portions of mainland Alaska and the Aleutians, Sat-Mon, Sep 25-Sep 27. 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