Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EST Thu Dec 13 2018 Valid 12Z Mon Dec 17 2018 - 12Z Fri Dec 21 2018 General elongated troughing becomes reinforced during the day 4-6 (Mon-Wed) time period by a couple of shortwaves moving into the Gulf. This sends a couple of deep surface lows northward through the Gulf, weakening as they move inland. Upper ridging builds across the Bering Sea during the same time, while another upper level trough and associated deep surface low drops south and eastward across or just south of the Aleutians. Models and ensembles show good clustering in the day 4-5 period, with uncertainty in the details and timing arising by day 6 and beyond. Despite some timing differences, there is pretty good agreement on the overall synoptic pattern in the ensemble means through the whole period. The WPC suite of Alaska progs for the 4-8 day period used a majority blend of the deterministic 00z ECMWF with the 12z GFS for days 4 and 5, transitioning to a total ensemble mean blend (between the 06z GEFS/00z ECENS/00z NAEFS) by the end of the period. Regarding sensible weather threats, expect widespread moderate to locally heavy rainfall to continue through the first half of next week across the panhandle and possibly extending into parts of the southern coast as a pair of deep surface lows moves northward through the Gulf. Gusty winds and high waves will accompany these systems as well with general cloudy and showery conditions farther inland across interior portions of Alaska. Conditions improve for coastal locations mid to late week, but showers may persist as general troughing continues. Organized moderate rainfall and gusty winds also look to impact parts of the Aleutians by Wednesday/Thursday ahead of an approaching low pressure system. Santorelli 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