Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 717 PM EDT Tue Sep 12 2023 Valid 12Z Sat Sep 16 2023 - 12Z Wed Sep 20 2023 ...Potent storm series offers heavy rain/wind threats from Southcentral to Southeast Alaska... ...Synoptic Overview and Guidance Evaluation/Preferences... The 12 UTC GFS/ECMWF/UKMET/Canadian models seem to offer reasonable flow embedded storm system commonality into the weekend in an energetic and progressive flow regime with a less certain but growing Southwest Pacific tropical influence including potential ejection into the westerlies of potential JWTC invest system 93W along with long fetched deep moisture. A favored model composite seems to provide good forecast detail consistent with a pattern with near average predictability this weekend. Fast building forecast spread and uncertainty into next week prompted a quick transition to the broader 12 UTC GEFS/NAEFS/ECMWF ensemble means at the cost of less defined but still organized individual weather features/storms despite remaining in an overall pattern that should still favor additional activity. ...Pattern Overview and Weather/Hazards Highlights... A series of potent low pressure systems will track progressively from across the North Pacific and the Aleutians and through the Gulf of Alaska with translation over the next week underneath a mean/amplified upper trough position centered over the Bering Sea/Strait and western Alaska. These systems will help direct long fetch moisture/atmospheric river/south-southwesterly flow into the Southern Coast/Southeast Alaska resulting in the potential for multiple days of very wet weather and heavy rainfall. Some locations could receive upwards of 4 to 8 inches of rain over the entire forecast period, with the greatest totals expected across the windward terrain of the southern and southeastern coastal mountain ranges. These storms should prove to be periodic significant maritime hazards. Very gusty winds/waves are possible into the coast as well. Onshore flow beyond the weekend should continue unsettled conditions across the Aleutians/AKpen/Kodiak Island and downstream to southern and southeast Alaska. Otherwise, much of the remainder of the mainland looks to remain mostly dry through the period. However, enhanced moisture should work more earnestly into southwest and western Alaska early-mid next week with slow Bering Sea upper low progression, but there is still a lot of uncertainty in the details. In terms of temperatures, expect readings to generally be below average across southern portions of the state owing to both persistent upper troughing/waves of cooler air and increased clouds and rainfall coverage. Temperatures will be around to above average further north into the Interior and North Slope. Schichtel Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Fri-Sun, Sep 15- Sep 17. 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