Alaska Extended Forecast Discussion National Weather Service College Park MD 701 PM EDT Fri Jun 13 2025 Valid 12Z Tue 17 Jun 2025 - 12Z Sat 21 Jun 2025 ...Guidance Evaluation/Preferences... The medium-range forecast period for the Alaskan domain through next Saturday morning will feature an omega blocking pattern, comprising of a closed 500-mb anticyclone over northern Alaska, a synoptic-scale vortex centered over the Bering Sea, and another vortex over the Gulf of Alaska. In this stagnant blocking pattern, the Bering Sea vortex is forecast to drift very slowly southward only to approach the Aleutians by late next week as the Gulf of Alaska vortex slides southeast toward British Columbia/Pacific Northwest. Model guidance today continues to show fairly good agreement on this overall synoptic pattern evolution, but with the deterministic guidance showing more spread on handling how troughing from the North Pacific may interact with the slow-moving Bering low by the end of next week. The 00Z EC ensemble mean is distinctly different from the GEFS and CMC means, with the 500-mb Bering Sea low generally lagging farther behind (farther north) than the GEFS and CMC, while the surface cyclone remains weaker and farther south than the GEFS and CMC mean solutions. In contrast, the 12Z ECMWF's solution shows a fairly solid cyclone passing the Aleutians from south to north by next Friday. A composite blend of the deterministic and ensemble means yields a solution fairly compatible with yesterday's WPC medium-range forecasts. In addition, this solution indicates that the omega block across the Alaskan domain may begin to break down and open up the overall stagnant upper-air pattern by next weekend. The WPC Alaskan medium forecast package was derived from a composite blend of moderately well-clustered guidance comprising of 40% from the 12Z ECMWF and 00Z/12Z EC mean, 40% from the 06Z+12Z GFS and 12Z GEFS, and 20% from the 12Z Canadian and its ensemble mean. The composite blend transitions to mainly a blend of the ensemble means by Day 7 & 8. ...Weather/Hazards Highlights... No hazardous weather is forecast for the Alaskan domain through the medium-range forecast period. Areas of showers and possibly embedded thunderstorms are forecast for the interior sections of western Alaska and into south-central mainland to begin the forecast period next Tuesday. These activities are expected to linger into Wednesday to the west of an inverted surface trough and a diffused stationary front that extends through eastern mainland. Meanwhile, a good chance of rain is expected from the southern coastline to the Panhandle as a stream of moisture advancing eastward from the Gulf of Alaska low reaches into the Panhandle. Some scattered showers can also be found near the Brooks Range under the presence of diurnally-forced instability. Meanwhile, rain chances are expected to gradually increase from west to east for the Aleutians through midweek and especially late next week as ensemble means indicate a good chance for the next Pacific cyclone to approach the region. Moderate to locally heavy rain could reach the eastern Aleutians into the southern Alaska Peninsula where a triple-point low pressure wave ahead of the main cyclone could develop and pass just to the south of the Aleutians. Under the influence of the slow-moving upper anticyclone over northern Alaska for much of next week, afternoon temperatures are expected to soar well into the 80s for the eastern interior especially across the Yukon Flats but a slow moderation of the heat is forecast heading into late next week. Kong Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook 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