Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 PM EDT Fri May 04 2018 Valid 12Z Tue May 08 2018 - 12Z Sat May 12 2018 ...Guidance/Predictability Assessment and Preferences... Model and ensemble guidance continues to cluster better than average in the mid to latter portions of next week due to the high amplitude and slow forward motion of systems. This bolsters the forecast to above normal confidence levels. Deep layered ridging builds from NW Canada to the Alaskan interior/North Slope next week as the initial potent upper low persists in the southern Bering Sea, gradually weakening later in the week with a new triple point low forming further south in the north Pacific. The new triple point low drifts east across the north Pacific, with the 06z GFS and GEFS members lowering heights/pressure a bit faster than the ECMWF and Canadian ensemble members and consequently the ensemble means as well. Given the long term bias of the GFS to move closed lows too fast, less weighting was given to the 00-06z gfs solutions later next week. More weighting was given to the slower 12z GFS. In the early to middle portions of next week, a 12z GFS/00z ECMWF/00z Canadian global /00z ECMWF ensemble mean blend was used since these solutions cluster well. This results in above normal heights/temperatures continue for interior Alaska in the middle to latter portion of next week. The persistent rainfall coverage is across southern AK, with shower chances gradually increasing further east towards southeast AK with height falls and increasing layer relative humidity later next week. Petersen 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 www.wpc.ncep.noaa.gov/alaska/akmedr.shtml http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html