Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 619 PM EST Thu Mar 05 2020 Valid 12Z Mon Mar 09 2020 - 12Z Fri Mar 13 2020 ...Overview and Guidance/Predictability Assessment... Model and ensemble guidance shows a moderate progression of features during the period. During the Mon-Wed time frame expect a couple streams of shortwave trough energy to promote surface low pressure over the Gulf of Alaska, followed by a southeastward departure as the dynamics aloft continue to the east. A weakening wave/frontal system will likely cross the Bering Sea around midweek. Then a strong and broad storm system should reach a position just northwest of the mainland by early next Fri after tracking over or west of Japan and Kamchatka earlier in the week. Regarding forecast specifics, one question mark involves the exact details of low pressure from south of the Alaska Peninsula into the Gulf during the first half of the week. Based on 12Z guidance there is a split between two general scenarios: 1. a developing system tracking south of the Peninsula and replacing a leading wave over the northern Gulf as of early Mon (UKMET/CMC); 2. a more subtle representation of the western wave initially and either farther east development in the Gulf or reinforcement of the initial Gulf low (GFS/ECMWF). Perhaps not surprisingly given that the means are averaging many solutions, they depict only one Gulf low through this time frame. The fine-scale nature of important shortwave details that will influence surface evolution suggests it may take into the short-range period to resolve. Therefore current preference is an intermediate approach with a 60 percent tilt to the GFS/ECMWF relative to the UKMET/CMC. Also this approach represents consensus well for the weakening wave tracking over the western Bering into midweek and associated frontal system. Overall guidance agreement is better than average in principle for the strong and broad northeastward-moving system expected to reach northwest of the mainland by early Fri. There is typical spread and run-to-run variability with strength and track/timing, favoring a transition of the forecast to a model/ensemble mean blend by Thu-Fri. Latest GFS runs are a bit on the faster/eastern side of the full guidance spread but not to an extreme degree for the extended nature of the forecast with the GEFS mean also moderately faster than the ECMWF/CMC means. During the past couple days the ECMWF/ECMWF mean have been more stable with the general evolution of this system versus the GFS/GEFS mean. Thus the late-week model/mean blend tilts a bit more to the ECMWF/ECMWF mean scenario than the GFS/GEFS (with modest CMC weight maintained as well). ...Weather Highlights/Threats... Early-mid week Gulf of Alaska low pressure will support enhanced precipitation along the Alaska Panhandle with somewhat lesser amounts extending back to the southeastern coast of the mainland. Expect this activity to trend lighter by the latter half of the week. Meanwhile cold high pressure building into/across the state from west to east will bring a period of much below normal temperatures. Readings will moderate late in the week, again from west to east, ahead of the system forecast to track across Siberia and just northwest of the mainland. This system will likely bring a broad moisture shield into the mainland Thu-Fri with fairly strong winds helping to enhance precipitation totals over favored terrain. 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 Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Mar 9-Mar 10. - Much below normal temperatures for the outer islands of western Alaska, Mon, Mar 9. - Much below normal temperatures across western Alaska, Mon-Tue, Mar 9-Mar 10. - Much below normal temperatures across central to eastern Alaska, Tue-Thu, Mar 10-Mar 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