Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 334 PM EDT Thu Oct 17 2019 Valid 12Z Mon Oct 21 2019 - 12Z Fri Oct 25 2019 The most significant system of interest during the period continues to be the potentially deep storm that may track toward or to either side of the Alaska Peninsula in the Tue-Thu time frame. Most individual models have been offering a general signal for this development but with considerable timing and track spread due to differences in how northern stream/Bering Sea energy may interact with a wave that emerges into the western Pacific during the weekend. Ensemble members have been sufficiently diverse that the means (especially the ECMWF mean) are much weaker than a number of operational runs. However the ensemble means have been more stable with an intermediate track/timing so preferences continue to lean toward their overall scenario (more to the 06Z GEFS mean due to its deeper surface low) but with some operational input where possible and manual adjustment to ensure the central pressure reaches at least into the 980's mb while awaiting better agreement. With the remaining 12Z models having come in, the UKMET has introduced a deep storm (versus none in the 00Z run) while the CMC/GFS are fastest with northward progression and the ECMWF is still a bit in the eastern half of the spread (though similar to the 06Z GFS). The 12Z GEFS mean has trended a bit westward. This storm will bring a potential for a period of strong winds/high waves. Best confidence for highest precipitation totals is from the Kenai Peninsula to the Panhandle, with areas westward into the Alaska Peninsula also seeing meaningful potential for enhanced precip. Elsewhere... Farther west most operational model runs are siding with the ECMWF mean with respect to the general idea of a system affecting the Aleutians by the latter half of the week. Specifics vary a lot though, so the manual forecast is fairly conservative in the depiction of the surface low. Early in the period guidance is still in the process of resolving multiple surface low centers/frontal systems across the Bering and northern-northeastern Pacific, favoring a model/ensemble mean blend to capture the most agreeable aspects of guidance. Across the higher latitudes, guidance has so far been showing a variety of possible evolutions for an Arctic upper ridge and an upper low that may retrograde to the south of the ridge. Overall the average of guidance has shifted somewhat westward with the upper low versus 24 hours ago highlighted by the 00Z CMC and 12Z GFS/GEFS mean. This type of evolution tends to have below average predictability so again a model/mean blend looks best for producing a single deterministic forecast. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Alaska Hazards... - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Wed-Thu, Oct 23-Oct 24. - High winds across portions of mainland Alaska and the Aleutians, Wed-Thu, Oct 23-Oct 24. - High significant wave heights for coastal portions of mainland Alaska and the Aleutians, Wed-Thu, Oct 23-Oct 24. 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