Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 339 PM EDT Sun Sep 08 2019 Valid 12Z Thu Sep 12 2019 - 12Z Mon Sep 16 2019 From day 4 Thu into day 5 Fri there is good agreement/clustering for the deep Bering Sea storm that represents the extratropical evolution of Lingling and in some fashion incorporation of Faxai (which is currently near Japan). Over the past day the ensemble means have trended deeper at the surface and aloft toward prior operational model consensus. Thus a blend of operational guidance continues to provide a good starting point for the Bering storm as well as a leading frontal wave forecast to be near the Kenai Peninsula by early Fri and track eastward thereafter. The same is true of a weakening surface low to the south of the Panhandle. Immediately behind these features the model and ensemble guidance rapidly diverges (among each other and between consecutive runs) for specifics of shortwave energy that emerges over the western Pacific, with significant influence on forecast details eventually extending as far east as the mainland and Gulf of Alaska. Up to the arrival of the 12Z GFS, there was a split in most recent solutions--latest GFS runs and 00Z ECMWF closing off a slow closed low versus the 00Z CMC/UKMET/NAVGEM with a phased progressive trough. Ensemble members spanned the full range of operational possibilities but with a majority progressive enough to yield a broad trough in the means. Poor continuity in 12-hourly operational runs up to this point favored trending the days 6-8 Sat-Mon forecast mostly to the ensemble means (with 10 percent of the 00Z CMC whose pattern was closest to the means) to preserve a reasonable degree of continuity until some confidence could be gained for significant adjustments. Note that among the means the ECMWF mean has been the most stable and thus merited the highest weight in the blend. This approach would bring the weakening Bering Sea trough/upper low into the southwestern mainland/Gulf while surface low pressure settles over the Gulf. The remainder of 12Z guidance suggests an increasing probability that the western Pacific energy will separate to some degree but not to the extent of the 12Z GFS. Maintaining some progression appears more plausible given the progressive pattern already in place and progression of upstream flow. However it is still quite early to have any confidence in a specific scenario such as the 12Z ECMWF/CMC that ultimately show interaction between their western Pacific to southwestern mainland storm and the upper low over the northern Bering. During the latter half of this week expect a broad area of enhanced winds around the initial Bering Sea storm with leading moisture bringing significant precipitation to parts of the southwestern mainland/southern coast with lesser amounts eventually extending into the Panhandle. The latest model trends are increasing the potential for another episode of enhanced wind/precip from the Aleutians into southwestern mainland by the weekend--but with confidence too low to depict in the deterministic forecast so far due to poor guidance agreement/variability. 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 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