Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 634 PM EDT Tue Jun 02 2020 Valid 12Z Sat Jun 06 2020 - 12Z Wed Jun 10 2020 ...Overview and Guidance/Predictability Assessment... The best cluster of guidance shows an eastern Bering Sea upper low gradually tracking across or near the Alaska Peninsula and into the northeastern Pacific, in the process interacting with a mid-latitude system forecast to be over the Central Pacific at the start of the period. Farther north a compact upper shortwave/low will likely track over the northeastern mainland underneath a weakening upper high during the first half of the period. The pattern aloft over the mainland should trend toward modest east-west ridging by next Tue-Wed, between the Northeast Pacific upper low and an Arctic upper low that comes into the picture northwest of the mainland. The primary forecast problem involves the eastern Bering to northeastern Bering upper low and surrounding flow. Up to this point there has been considerable variability for the specifics, including among the last two ECMWF runs which were complete opposites--keeping it over the Bering (00Z) or progressing into the Pacific (12Z). Beyond that the 12Z GFS varied the details of the low and surrounding flow such that it compared less favorably to the means than the 06Z run over a sizable area. Before today the GEFS mean had been faster with the upper low versus the ECMWF mean but a slower trend in the 12Z cycle has brought it closer to the ECMWF mean that has maintained continuity fairly well into the new 12Z version. Also of note, the 12Z GFS was a bit on the slow side with the mid-latitude Pacific system reaching the Northeast Pacific. Over higher latitudes the 12Z CMC leaned to the extreme side of the spread with height falls extending into the northwestern mainland by next Tue-Wed. 12Z ECMWF/06Z GFS/12Z UKMET runs provided the initial basis of today's forecast for days 4-5 Sat-Sun. Then the blend increased 12Z GEFS/00Z ECMWF mean weight as operational model details diverged somewhat, reaching 50-60 percent by days 7-8 Tue-Wed. Compared to continuity the new forecast reflects increased definition of the initial eastern Bering upper low followed by a somewhat farther north track of Pacific low pressure due to the stronger upper dynamics. Over the mainland some precise details at the surface changed but the tendency for thermal lows/troughs will persist. ...Weather Highlights and Hazards/Threats... Expect periods of convection over favored terrain from this weekend into next week. The upper low tracking over/near the Alaska Peninsula may also support some precipitation over and southwest of the southwestern mainland during Sat-Mon. Activity near the Peninsula may linger beyond Mon if low pressure ends up tracking on the northwestern edge of the current envelope. Otherwise the surface low should remain far enough south to keep associated precipitation over water next week. For temperatures expect a mix of above/below normal readings depending on location/elevation. In general southern areas including the Panhandle should see more below normal highs while the north will likely see somewhat more above normal highs. There should be greater coverage of above normal low temperatures during the period. 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