Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 721 PM EDT Thu Aug 24 2023 Valid 12Z Mon Aug 28 2023 - 12Z Fri Sep 01 2023 ...Multi-day Heavy Rainfall Threat for South-central Alaska next week... ...Guidance Evaluation/Preferences... The 12 UTC GFS/ECMWF/UKMET/Canadian seem reasonably compatible for early next week in an active pattern with average predictability and ensemble support, albeit with plenty of uncertainties in the details and timing of individual systems over time. Forecast spread increases for mid-later next week, but a blend of the 12 UTC GFS/ECMWF and GEFS/ECMWF ensemble means along with manual adjustments to maintain/deepen offshore low pressure systems given support seems to provide a reasonable solution best in line with the amplified flow and also with the expected stormy ejection toward Alaska of deep extratropical low associated with current west Pacific tropical system Eight. ...Weather/Hazards Highlights... Wet weather associated with an exiting upper system/lingering front across northern Alaska this weekend is forecast to give way to drier conditions by early next week as high pressure moves over the region. Meanwhile, a multi-day heavy rain event will repeatably focus over the South-central Alaska and vicinity all next week, extending quite a wet and unsettled pattern as several deepened lows and deep moisture work into the region. Several leading and organized surface lows will rotate/lift out from the Aleutians and also the northeast Pacific through the Gulf of Alaska and inland into early-mid next week as fueled by long fetch moisture plumes/atmospheric rivers in advance of an amplifying Bering Sea centered upper through. The combination of moist storms and cumulative affect of multiple systems/rainfall offers a threat for runoff problems. There is then an upstream signal that still uncertain system energies from tropical "Eight" currently in the West Pacific may approach the Alaska domain next week, helping to deepen an associated extratropical surface low that moves in towards the central-eastern Aleutians through next midweek, then potentially onward to the mainland into mid-later next week to fuel an additional heavy rain and maritime to coastal wind threats. In terms of temperatures, the coldest anomalies (10-20F below normal for daytime highs) will linger Monday across the northern interior of Alaska and the Brooks range as upper troughing moves through. Otherwise, temperatures across much of the state will moderate closer to normal and above next week as upper level ridging builds into the region. Schichtel 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 Hazards: - Heavy rain across portions of northwestern mainland Alaska, Sun, Aug 27. - Heavy rain across portions of southern mainland Alaska, Sun-Tue, Aug 27-Aug 29. 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