Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 748 PM EDT Sun Jun 06 2021 Valid 12Z Thu Jun 10 2021 - 12Z Mon Jun 14 2021 ...Overview and Guidance Evaluation... There are still stray solutions that differ but today's model and ensemble guidance is generally better clustered for the large scale pattern. Over the past day consensus has finally converged toward the idea of the short-term upper low over/near the far western mainland ejecting to the north-northeast in response to upstream troughing. The majority of guidance shows this mean trough amplifying and eventually interacting with a western Pacific feature that should track into the Aleutians--most likely yielding an upper low over the eastern half of the Bering Sea by the start of next week. Today's forecast blend started with a blend of 12Z operational models, ECMWF/GFS/UKMET/CMC in order from most to least weight, for the first two days of the period to depict the most agreeable aspects of guidance while blending lower confidence details. Then the forecast trended to 40-60 percent total weight of the 12Z GEFS/00Z ECens to provide a slightly enhanced ensemble depiction of the system tracking into the Aleutians/Bering Sea while staying close to the means over the mainland where models differ significantly over some details. Even with the outcome of the short-term western mainland upper low closer to being resolved, there are still other detail uncertainties in the guidance. The majority shows shortwave energy that reaches near the southwest corner of the mainland as of early Thursday dropping well southward into an eastern Pacific mean trough/low. However there is still some spread for the character of this energy and the new 18Z GFS has a particularly low-confidence evolution of it closing off an upper low that remains over the mainland for most of the period. From late week into the weekend the ensemble means provide a good middle ground between the offsetting 12Z ECMWF cyclonic flow (around a Bering Strait upper low) and 12Z GFS ridge. The means agree that flow should evolve toward a western Canada into mainland mean ridge late in the period as the upper trough/low reaches the eastern Bering Sea. The North Pacific into Bering evolution still has a fair degree of uncertainty for specifics. Recent ensemble means have been trending toward more stream interaction which the operational models had been suggesting, thus nudging the main surface low a bit eastward. Otherwise the means have been fairly stable. In contrast, consecutive GFS runs have been particularly inconsistent lately. Today's 06Z/18Z runs are quite progressive and suppressed for the leading wave which pushes into what the remaining consensus says will be a mean ridge. The 12Z GFS was just close enough to other guidance to include in a compromise with the ECMWF/CMC to enhance the ensemble low depth a bit. ...Weather/Threats Highlights... Precipitation from the eastern Alaska Peninsula to the Kenai Peninsula and vicinity may extend into Thursday before a brief drier trend. Meanwhile shortwave energy of uncertain strength could help to produce scattered areas of precipitation farther north over the mainland. Confidence is low in the details of coverage and intensity due to significant model spread for specifics of flow aloft. The system expected to track into the Aleutians and Bering Sea should spread moisture into the Aleutians late this week into the weekend and then the southwestern mainland and vicinity by next Sunday-Monday. Some areas could see a period of brisk winds/enhanced rainfall depending on the strength and track of the system. Below normal highs over much of the state as of Thursday should gradually moderate from the southwest with time, yielding various areas of above/below normal highs by early next week. Low temperature anomalies should be fairly modest on either side of normal from late week into the weekend. Interior and western areas along with parts of the Panhandle are most likely to see below average readings with remaining areas near/above normal. By Sunday or Monday there may be greater coverage of above normal lows and with somewhat higher anomalies. 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 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