Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EST Tue Mar 05 2019 Valid 12Z Sat Mar 09 2019 - 12Z Wed Mar 13 2019 Today's guidance continues to show better than average agreement and continuity in principle as the pattern evolves toward a mean trough aloft becoming aligned near the western coast of the mainland. A shortwave embedded within progressive North Pacific flow may phase with this trough by around next Wed, leading to the possibility the overall trough could take on a negative tilt. This pattern should lead to one or more periods of focused precipitation along the southern coast and Panhandle along with episodes of strong winds/high waves from the Aleutians eastward. The portion of the forecast spanning day 4 Sat into day 6 Mon incorporates ideas from the 00-06Z GFS and 00Z ECMWF/CMC. There was a robust cluster of 00-06Z operational models showing eastern Bering triple point development tracking toward the western mainland while the deep parent low over the western Aleutians as of early Sat (950's mb, similar to yesterday's forecast) tracks eastward along the Aleutians while weakening. The ensemble means merged the two separate lows. Interestingly the new 12Z GFS has come in with a merged scenario but on a track a little south of the means. Thus confidence in exact details is not exceptionally high. Other 12Z runs vary in specifics but do agree on an overall low track to the north of the 12Z GFS. By day 6 Mon the operational runs show better definition than the means with another wave tracking near the Aleutians, favoring continued operational model emphasis through mid-period. By days 7-8 Tue-Wed the forecast rapidly adjusts toward a more even blend of model and 06Z GEFS/00Z ECMWF mean solutions. Guidance shows a general theme of surface low pressure emphasis transitioning from the western mainland into the northeastern Pacific as a reflection of potential phasing of North Pacific shortwave energy with the upper trough near the western coast of the mainland. The most likely scenario has low pressure tracking within an area to the south/southeast/east of Kodiak Island by day 8 Wed. Especially by late next Wed the ECMWF mean and operational runs all display deeper/eastward low pressure than the 06Z GEFS mean to varying degrees with the ECMWF mean more stable over the past day and GEFS means showing an eastward trend over recent runs. As a result the preferred blend leans more toward the majority cluster. Meanwhile operational models are generally faster than the means with another North Pacific/Aleutians wave that comes into the picture by next Wed. The model/mean blend provides a good middle ground between the two clusters. Across the Arctic there is decent agreement that during the weekend into early next week flow aloft will gradually amplify to the south of an upper low drifting along near 80N latitude, with the preferred blend resolving differences in amplitude--GFS/GEFS guidance generally deeper than other solutions. By Tue-Wed the upper low/trough should drift far enough eastward to allow for expansion of surface high pressure north of the mainland. Rausch Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Tue, Mar 10-Mar 12. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sat-Tue, Mar 9-Mar 12. - High winds across portions of mainland Alaska, Sat-Sun, Mar 9-Mar 10, and for the Aleutians, Fri-Tue, Mar 8-Mar 12. - High significant wave heights for coastal portions of the Aleutians, Fri-Sun, Mar 8-Mar 10. WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can 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