Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 223 PM EDT Sat Aug 17 2019 Valid 12Z Wed Aug 21 2019 - 12Z Sun Aug 25 2019 A blend of the 00Z EC ensemble mean and the 06Z GEFS mean, together with a smaller portions of the deterministic 00z ECMWF/00z Canadian/06z GFS were used to generate the 500 mb height forecasts and sea level pressures/fronts and gridded probability of precip and wind fields for days 4 to 8. Following the Wed low moving onshore into southeastern Alaska Wednesday, the next system upstream develops in the north Pacific south of the Aleutians. On Thu, the low drifts east with a possible triple point low developing well south of Kodak Island. The 12z GFS there in an outlier solution of a rapidly deepening low further east with its low forecast at 00z Fri near 54n 138w. I would prefer to wait for better continuity and model and model agreement on this development, so the 12z GFS was not used in the blend. The ECMWF and 06z GEFS ensembles indicate the possibility of a few waves of low pressure in the Gulf of AK to southeast AK next weekend. The gfs holds the axis of low pressure int he north Pacific further southwest than the other models. With a general cluster of lows over north Gulf of AK and northern Pacific, a general ensemble mean and model blend was sued to mitigate differences. Over the Arctic Ocean, persistent low heights and a few waves of low pressure are forecast this period. Several models and ensembles indicate a wave on the front developing on days 4-5 as the system drifts east. The 12z GFS and 00z Canadian ensemble mean even have another wave developing at the base of the trough next weekend, so the area will be monitored for these developments. The 00z ECMWF was given less weight as it moves the upper trough east faster than most models/ensemble members. More weighting was given to the 06z GEFS Mean and 00z ECMWF Ensemble Mean as a result. Petersen 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 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