Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 750 PM EDT Tue Aug 08 2023 Valid 12Z Sat Aug 12 2023 - 12Z Wed Aug 16 2023 ...Storm system will bring heavy rain to Southcentral and Southeast Alaska this weekend along with a mainly maritime high wind threat... ...Overview... An upper/surface low remains likely to move through the Gulf of Alaska toward Southcentral/Southeast Alaska this weekend, spreading heavy rain into those areas. The highest winds look to remain offshore but could be a maritime threat in the Gulf, and some gusty winds may sneak into coastal areas. Farther west, an upper low looks to sit near the Aleutians/Bering Sea into next week. A west-east oriented ridge axis farther north across northern Alaska late this week is likely to retreat early next week as troughing influences from the aforementioned upper lows and perhaps some energy from another upper low well northeast of Alaska should combine to create a more troughy pattern stretching from the Aleutians northeast across the Mainland. ...Guidance Evaluation/Preferences... Model guidance is mostly in broad scale agreement with the pattern described above, but detail differences remain, first with the surface low placement in the Gulf on day 4/Saturday. In the 12Z model cycle, the ECMWF was on the west side of the spread along with the bulk of its ensemble members. Meanwhile the UKMET was farther east of consensus, while GFS and CMC runs appeared to be more of a middle ground, so favored those latter solutions in the model blend early in the period. But into early next week, the 12Z GFS diverged from consensus by splitting some energy east toward Kodiak Island that most models (and its 06Z run) showed remaining near the Aleutians. The CMC seemed to be reasonable through around Monday but then diverges from consensus as strong shortwave energy rounds the southern side of the upper low and creates troughing in the northern Pacific/Gulf where other guidance is building ridging from a strengthening upper high well offshore of the Pacific Northwest. Despite the ECMWF pattern at the start of the period, it seemed to fit reasonably well with the ensemble means later at 500mb in particular, though was quite strong with a surface low in the northern Pacific by the end of the period next Wednesday, without much support at this lead time. Thus as the GFS and CMC were phased out of the model blend for the most part, increased the weighting of the GEFS and EC ensemble means that were more agreeable to around 75 percent of the blend by Day 8. ...Weather/Hazards Highlights... While there are still some forecast uncertainties in the exact surface low position in the Gulf to Southern Coast, at least models generally agree that the low will be relatively strong for summertime and that it will help create heavy rainfall perhaps on the order of 2-4 inches per day peaking on Saturday across southeastern Alaska as an atmospheric river takes aim ahead of the low. Additionally, the strength of the low could produce gusty winds over the Gulf of Alaska and perhaps reach coastal areas generally from Kodiak Island east across the Southern Coast over the weekend. Into early to mid-next week, moist southwesterly inflow could lead to additional rounds of rain that may be enhanced along the Southern Coast once again and in the terrain of the Alaska Range, but at this point heavy rainfall does not look to be as widespread as over the weekend. High temperatures should stay a bit cooler than normal in the southern part of the state given the rain chances and cloudiness. But the upper ridge impacting northern Alaska should lead to warmer than normal temperatures farther north, except for the North Slope where oceanic flow should keep that area cool. Temperatures are likely to moderate closer to normal for the Brooks Range to Interior into next week as the ridge breaks down in favor of upper troughing. Tate 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 - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Sat, Aug 12. 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