Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 136 PM EST Fri Feb 01 2019 Valid 12Z Tue Feb 05 2019 - 12Z Sat Feb 09 2019 Amplified flow is expected to persist from the North Pacific to Alaska during the extended period. A mean trough will persist across the Aleutians and portions of the Bering Sea, with downstream ridging from the Gulf of Alaska north into mainland Alaska. A number of systems will rotate through the mean Bering trough during the period, and models/ensembles showed relatively good consensus, especially with respect to the first couple. One weakening low pressure system is expected to be in place across the eastern Bering Sea on Tue, with a second deeper low entering the western Bering Sea. A frontal wave associated with the leading shortwave is expected to develop in the Gulf of Alaska Tue-Wed, but this feature should be relatively weak as it encounters anticyclonic flow aloft on the northern periphery of the upper ridge. The ECMWF and GFS solutions were well clustered with the ensemble means with these systems. Thus, a blend of these solutions served as a basis for the forecast starting on day 4 (Tue) and continuing into day 6 (Thu). During days 7-8 (Fri-Sat) models/ensembles continued to show good large scale agreement but solutions begin to differ with respect to the details. Another vigorous shortwave appears likely to cross the North Pacific with a surface low perhaps nearing the Aleutians. Some solutions/ensemble members keep this system a bit farther south while some take the low into the Bering Sea. Given the increased spread, opted to increase ECENS/GEFS ensemble means to comprise a majority of the forecast during days 6-7. This consensus blend shows a low crossing the western Aleutians on Fri and entering the western Bering Sea Fri night into Sat. Meanwhile, upper ridging should remain in place through the period from the Gulf north into eastern mainland Alaska. Models differ to some extent on whether any of the shortwaves will flatten the ridge and how much, but the general consensus is that a mean ridge should remain in place through the next week. Ryan WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can be found at: http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html