Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Sun Sep 17 2023 Valid 12Z Thu Sep 21 2023 - 12Z Mon Sep 25 2023 ...Guidance Evaluation/Preferences... The 12Z model guidance suite is initially in good agreement late in the week, but model spread increases substantially going into the weekend and beyond with the timing and magnitude of storm systems crossing the Bering and the Gulf of Alaska. The CMC is likely too far north with the low entering the Bering Sea by Saturday, so a solution between the ECMWF/GFS was favored. The use of the ensemble means increased to about 50-60% by Sunday and Monday owing to increased uncertainty. ...Pattern Overview and Weather/Hazards Highlights... There remains a strong guidance signal in this continued stormy pattern in support of additional deep low development and track into/across the southern Bering Sea and Aleutians out from early next week along with an enhanced maritime risk and wrapping heavy rainfall/winds. Steady downstream deep energy transfer should lead to the potential storm, with aforementioned risks spreading past southwest Alaska, the Alaskan Peninsula and Kodiak Island Tuesday into Wednesday, and then Southcentral to Southeast Alaska in earnest by Wednesday into next Thursday, lingering into Friday. This system will likely tap a deep layered and long fetched atmospheric river with low latitude origins to fuel rainfall. Farther north, a closed upper low will settled over northwest Alaska into mid next week may slowly weaken and eject into the Arctic Ocean later next week or alternately linger over the North Slope/Interior. This system seems amplified enough aloft along with an organized surface system to support unsettled conditions, especially early-mid next week, to include broadly scattered precipitation in proximity of the system and with the added terrain effect for some Brooks Range snows. Upstream, another deep low in this powerhouse series may meanwhile work into the Bering Sea next Thursday/Friday that is likely to spread threatening weather to the western mainland heading into next weekend, likely with a farther northward track/effect than the previous stream of systems given favorable guidance trends. In addition to a maritime hazard, this system may offer enhanced precipitation and winds along with the potential for amplified coastal impacts. Schichtel/Hamrick 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