Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Thu Sep 7 2023 Valid 12Z Mon Sep 11 2023 - 12Z Fri Sep 15 2023 ***Heavy rainfall likely over portions of South-central to Southeastern Alaska into next week*** ...Synoptic Overview... An upper trough is expected to extend from northwest to southeast from Siberia into the western Mainland and the Gulf of Alaska through much of next week, with embedded upper lows. Surface lows focused in the Gulf directing moisture inland into coastal areas could lead to multiple rounds of potentially heavy rainfall. The highest precipitation totals are likely from parts of South-central into Southeast Alaska. ...Guidance Evaluation/Preferences... Recent model guidance has persisted in indicating this trough pattern across much of the state, with the negatively tilted orientation of the trough possibly allowing some ridging from western Canada to push into the northeastern part of the Mainland. Differences become substantial from Wednesday on across the Bering Sea and the western Aleutians regarding the timing of the next storm system. The CMC is most out of phase with a ridge building into the western Bering, whereas the GFS/ECMWF support more of a shortwave and surface front. By next Friday, the GFS becomes much stronger with a low developing over the Gulf region compared to the model consensus. Given the uncertainty of shortwaves arising from eastern Siberia, confidence is below average in any particular solution. Thus gradually increased the ensemble means from the GEFS and ECENS as the period progressed, ending up to just over half by the end of the period. ...Weather/Hazards Highlights... The southeast portion of the mainland and the southeast Panhandle region will remain rather unsettled for much of next week with multiple rounds of enhanced moisture advected inland, which will be associated with low pressure systems over the northern Gulf region with the potential for an atmospheric river event or two. Some locations could get 3 to 6 inches of rain over the entire forecast period, with the greatest totals expected across the windward terrain of the coastal mountain ranges. In terms of temperatures, expect readings to generally be slightly below average across western portions of the state and slightly above for the eastern Interior to start the week. Going into the middle to end of the week, warmer conditions are likely across the northern two-thirds of the state, and slightly below average for the southern coastal areas owing to increased clouds and rainfall coverage. Hamrick Hazards: - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sun, Sep 10. 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