Alaska Extended Forecast Discussion National Weather Service College Park MD 648 PM EDT Thu Jun 12 2025 Valid 12Z Mon 16 Jun 2025 - 12Z Fri 20 Jun 2025 ...Guidance Evaluation/Preferences... The medium-range forecast period for the Alaskan domain through next Friday will feature a 500-mb ridge gradually closing off into a separate anticyclone over northern Alaska while two synoptic-scale vortices, one over the Bering Sea and another over the Gulf of Alaska, will meander over the same general vicinity. In this stagnant upper-air pattern, the Bering Sea vortex is forecast to drift very slowly southward only to approach the Aleutians by Day 8 while the Gulf of Alaska vortex may approach British Columbia by then. Model guidance today generally shows fairly good agreement on this overall synoptic pattern evolution, with the 12Z ECMWF and its ensemble means slightly faster in advancing the three main synoptic systems forward. Over the Aleutians, deterministic global model solutions continue to show a great deal of spread on the timing of the arrival of the next cyclone from the Pacific. However, ensemble means from the EC, GEFS, and CMC show solid agreement for the core of a cyclone to reach the western Aleutians by Day 8 Friday. 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 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. Continuity from yesterday's forecast package is well maintained. ...Weather/Hazards Highlights... No hazardous weather is forecast for the Alaskan domain through the medium-range forecast period. The lingering rainfall focusing on the south-facing shore of the southern Alaska Peninsula should begin to spread northeastward into southwestern Alaska as the forecast period begins next Monday. Heaviest rainfall is expected across the inland section of southwestern Alaska where totals could top one inch on Monday. Meanwhile, chances of rain will be on the increase from the southern coastline to the Panhandle as the Aleutian system merges with the Gulf of Alaska low. The southern interior sections and further up into portions of the western mainland and perhaps into the Brooks Range can expect an increasing chance of scattered showers and thunderstorms through much of next week under the presence of diurnally-forced instability near the northern edge of the Gulf of Alaska circulation. 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. 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