Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 745 PM EDT Wed Jun 09 2021 Valid 12Z Sun Jun 13 2021 - 12Z Thu Jun 17 2021 ...Overview and Guidance Evaluation... The main system of interest in the medium-range remains across the Aleutians. Since yesterday, there has been more of a split decision among the major model guidance on this system. The ECMWF switched quite abruptly to separate the upper trough dropping into the western Bering Sea with the southern wave that is forecast to pass to the southeast of the Aleutians. The CMC supported this split as well but the GFS still tended to merge the two systems. The ensemble means basically continue to advertise a main low moving across the Aleutians early next week. Therefore, the decision was to include more of the ensemble means starting on Day 5 to better agree with continuity for today. This solution keeps a double-barrel low moving eastward across the Bering Sea and the Aleutians Sunday and Monday, followed by gradual elongation of the system toward the Gulf of Alaska, with residual vortices near the Aleutians through next Thursday. This scenario is supported by the latest (12Z) EC means (not incorporated in this forecast package). A general model compromise among the 12Z ECMWF/00Z EC mean, 12Z CMC/CMC mean, and 12Z GFS/GEFS trending toward the ensemble means was used to compose the current medium-range forecast package. This yielded a more elongated low pressure system across the Aleutians to the Gulf of Alaska than yesterday's WPC forecasts. Elsewhere, a stationary front should remain draped across the northern portion of Alaska through the medium-range period. ...Weather/Threats Highlights... Precipitation associated with the upper shortwave edging in from Siberia should overspread the northern portion of Alaska on Sunday, and especially along the Brooks Range. The precipitation is expected to linger through midweek near a stationary front but is expected to slowly diminish with time. Meanwhile, the strengthening system that tracks into the Aleutians/Bering Sea will spread a broad area of moisture across the Aleutians and into much of the Alaska Peninsula early next week. The Aleutians should see a period of enhanced rain/winds on Monday as the occluded cyclone is forecast to reach peak intensity. Some enhanced rainfall will then shift eastward along the south coast of the Alaska Peninsula Tuesday and possibly Wednesday. Along the Alaska Panhandle, chance of precipitation will tend to increase through midweek. High temperatures will tend to be cooler than normal for the western half of Alaska through the medium-range period. For lows, expect slightly below normal readings over parts of the Interior and western mainland, while remaining areas should be above normal. The coverage of above normal lows should increase through midweek. Kong No significant hazards are expected over Alaska during this forecast period. 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