Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 403 PM EDT Wed May 15 2019 Valid 12Z Sun May 19 2019 - 12Z Thu May 23 2019 Once again forecast details are quite uncertain across a broad area covering the North Pacific, Aleutians/Alaska Peninsula, and the Bering Sea. Most guidance suggests this region will be under relatively low heights aloft with multiple embedded low centers, but agreement and continuity are quite poor regarding details. For example energy initially dropping into the Bering could become part of the overall cyclonic circulation which ensemble means show near the eastern Aleutians/southwestern Alaska Peninsula--or alternatively just meander over the Bering or drop farther south into the Pacific. At the same time various possibilities exist for one or more northeastern Pacific waves. Yet another major uncertainty involves the ultimate track and timing of mid-latitude low pressure which will be supported by an amplifying central Pacific trough and may eventually affect the Aleutians/Alaska Peninsula. Given poor model/ensemble member clustering and run-to-run changes, the forecast maintains a conservative approach over the above area by way of a model/mean blend, consisting of the 06Z GFS/FV3 GFS and 00Z ECMWF along with the 06Z GEFS and 00Z NAEFS/ECMWF means. The blend removes the 00Z ECMWF after day 6 Tue due to its run becoming farther west than consensus for the overall central-eastern Pacific pattern. Also the forecast leans slightly toward the operational runs early and 80 percent toward the means by days 7-8 Wed-Thu. Even the ensemble means have varied with their weak reflection of late period central Pacific low pressure. Overall trend from the past day is for slower arrival of this low but the new 12Z ECMWF adjusted faster from its questionable 00Z run and by day 8 Thu is not far from the manual forecast's timing. In spite of the detail uncertainties, around days 4-5 Sun-Mon there is relative agreement for a period of easterly low level flow that would enhance precipitation somewhat from the Kenai Peninsula to Kodiak Island and the Alaska Peninsula. Farther northeast the ensemble means have been fairly consistent in showing a Canadian ridge building over the northeastern mainland and possibly merging with a short range Arctic ridge. Operational runs show different ideas for ridge details, supporting a solution that transitions from a model/mean blend more toward the means with time. Based on stronger ensemble mean trends from yesterday and recent operational runs, the manual forecast enhanced the strength of the ridge relative to the initial blend described above. The ridge axis is close to continuity though. 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