Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 339 PM EDT Tue May 14 2019 Valid 12Z Sat May 18 2019 - 12Z Wed May 22 2019 Today's ensemble means agree well for large scale flow evolution. They show initial Aleutians through northeastern Pacific energy (with one or more embedded lows) trying to consolidate near the eastern Aleutians/southwestern Alaska Peninsula. Western Pacific mid-latitude trough energy should gradually progress into the central Pacific with some interaction possible. Farther east/northeast, the means expect upper ridging over Canada to build northwestward, eventually covering the northeastern mainland and possibly connecting with an upper high that reaches the Arctic in the short range time frame. Not surprisingly the spread among individual model runs and ensemble members would suggest much lower confidence in specific details. For the upper ridge, operational GFS runs continue to be on the stronger side of the spectrum. The 06Z FV3 GFS offers a compromise between the GFS and weaker means/ECMWF. Across the North Pacific and Bering, ensemble members lose any semblance of clustering after day 5 Sun over the former and already after early day 4 Sat over the latter. There is a general hint among the most compatible solutions that northeastern Pacific low pressure in some form may try to track back to the west, providing a period of enhanced--though not exceptional--low level easterly flow/precipitation to the southwestern coast/Alaska Peninsula. Meanwhile another uncertainty is the extent to which western-central Pacific troughing/associated surface reflection might interact with the mean upper low near the eastern Aleutians. The ECMWF/CMC ensemble means provide enough support for at least a conservative depiction of phasing in the manual forecast. Sporadic operational runs (e.g., 12Z/13 ECMWF and 00Z/14 GFS) have displayed much stronger low pressure but there is not yet enough agreement/continuity to depict in a single deterministic forecast. Energy that may drop southward over the Bering provides another wild card in the forecast. The manual forecast started with a model/ensemble mean blend consisting of the 06Z GFS/FV3 GFS and 00Z ECMWF along with the 06Z GEFS/00Z ECMWF means (plus some 00Z NAEFS late day 6 Mon onward due to having better low pressure definition vs the GEFS). The blend leaned 70 percent toward the models early in the period and then transitioned to 70 percent means by day 8 Wed, with minor manual adjustments as needed. Rausch 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 No significant hazards are expected over Alaska during this forecast period. 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