Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 727 PM EDT Mon Jun 07 2021 Valid 12Z Fri Jun 11 2021 - 12Z Tue Jun 15 2021 ...Overview and Guidance Evaluation... The extended forecast for Alaska and vicinity is finally becoming more straightforward as operational guidance is trending toward better agreement among each other and the ensemble means for shortwave energy crossing the mainland through the weekend followed by an upper ridge that builds in from Canada, as well as for the Aleutians-Bering Sea system that will be the dominant storm of interest during the period. A weaker trend in the 12Z ECMWF from its prior run yielded a good cluster among the GFS/ECMWF/UKMET for the shortwave forecast to progress eastward and then northeastward over the mainland early-mid period. The CMC was somewhat slower for a time. By next Monday-Tuesday the models and means all show the upper ridge building into the mainland from western Canada, with only typical detail differences for strength and axis location. The most noticeable trend in the models for the Aleutians-Bering Sea system is for stronger incorporation of amplifying Siberia/Kamchatka energy, leading to a deeper surface system. Ensemble means have recently been trending stronger as well. The 12Z ECMWF as well as the new 12Z ECMWF mean (not available at time of forecast preparation) adjusted significantly southward toward some of the other guidance by day 8 Tuesday. The 12Z GEFS/CMC means already suggested some degree of suppression at that time and the blend included the 12Z ECMWF so the forecast accounts for this adjustment. During the first half of the period the GFS/ECMWF/UKMET blend preferred over the mainland provided reasonable detail/strength for the Aleutians-Bering system as well. Transitioning the forecast toward about half models (GFS/ECMWF/CMC) and half means (12Z GEFS/00Z ECens) by day 8 Tuesday reflected the large scale agreement well and balanced detail/strength uncertainty. ...Weather/Threats Highlights... The upper shortwave expected to reach/cross the mainland late week into the weekend should promote periods of precipitation that should be best organized over about the northwest half of the mainland. Expect precipitation to become lighter and more scattered by late weekend and early next week as the shortwave departs and an upper ridge builds into the mainland from Canada. The strengthening system that tracks into the Aleutians/Bering Sea will spread a broad area of moisture across the Aleutians and possibly as far eastward as parts of the southwestern mainland. The Aleutians may see a period of enhanced rain/winds during the weekend and the Alaska Peninsula/Kodiak Island could see a couple days or so of focused rainfall during the first half of next week in the leading flow based on the current forecast track of the storm. Relatively cool high temperatures over a majority of the state late this week should gradually moderate with time as shortwave energy lifts to the north of the state by late weekend/early next week and then upper ridging builds. By late in the period the Panhandle and parts of Southcentral as well as portions of the northwestern mainland may still be somewhat below normal for highs. For lows, expect moderately below normal readings over parts of the Interior and western mainland as well as the Panhandle plus far southeast corner of the mainland, while remaining areas should be above normal. The coverage of above normal lows should increase toward Monday-Tuesday. Rausch 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