Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Mon Jun 10 2024 Valid 12Z Fri Jun 14 2024 - 12Z Tue Jun 18 2024 ...Overview... Guidance continues to show a blocky pattern aloft featuring a mean low over or near the Aleutians, along with ridging over the mainland into the central/northern part of the Bering Sea at least into the weekend. However latest solutions exhibit increasing divergence regarding the ultimate path of an upper low over or near far eastern Siberia as of early Friday. Thus from later Saturday onward over the mainland there is a range of possibilities from persistence of the upper ridge to significant height falls, especially over the northern half of the mainland. Strength/location/persistence of the warm upper ridge will influence the potential for fire weather concerns over portions of the mainland while the mean low near the Aleutians should support multiple days of unsettled weather over that region. ...Guidance Evaluation and Preferences... Over the past day or so, the ultimate path of the upper low initially over or near the eastern tip of Siberia as of early Friday has become an increasingly significant problem (but with its compact scale within a blocky pattern leading to low predictability) for the mainland forecast. Established consensus consisting of the ensemble means, machine learning (ML) models, and most GFS/ICON runs had been suggesting this upper low would lift fairly far northward with minimal influence on the mainland through the first part of next week. Some CMC runs have been dropping it into the mainland while an isolated ECMWF and UKMET run would have it lingering over the Bering Sea. Then the 12Z ECMWF switched to bringing the upper low across the northern mainland (though slower than the 12Z CMC) while the 12Z GFS gets close to the northwestern coast by next Tuesday. With the 00Z-06Z ML models still generally supportive of the ensemble means as solutions diverge, today's forecast favored keeping the upper low northwest of the mainland per the 12Z GFS (through Monday), 00Z ECMWF, and 12Z GEFS-CMCens/00Z ECens means. Newly arriving guidance does nudge toward more upper low influence, with the 18Z GFS dropping the upper low farther south than the 12Z run, the 12Z ECens mean trending a bit southeastward, and the two ML models that had the upper low closest to the northwestern mainland trending closer to the northwest coast. Meanwhile the ML models have been showing typical detail differences over the Aleutians/North Pacific but have been consistent in showing the mean low meandering over or just south of the Aleutians for most of the period. In general this evolution has been closest to an average of the ensemble means. The dynamical models have been more inconsistent with the details/latitude of what will likely be an initial feature and then reinforcement from additional energy arriving from the west. Today's dynamical models generally seem to agree better with each other and the ML/ensemble mean scenario than in recent days. The 12Z CMC offers the primary questionable solution, incorporating a mid-latitude Pacific wave to yield a stronger/wetter Aleutians system versus other guidance by Sunday. Guidance has come into good agreement with a northeastern Pacific upper low that should track to the south of Haida Gwaii late this week, with the primary effect on the mainland being easterly/northeasterly flow aloft to the north of the low. After the upper low departs, the pattern over the northeastern Pacific/Panhandle becomes increasingly uncertain due to aforementioned issues to the north. Forecast preferences led to starting with 70 percent total 12Z GFS/12Z-00Z ECMWF and 30 percent means (12Z GEFS/CMCens and 00Z ECens) for day 4 Friday, with the next couple days steadily phasing out 12Z ECMWF input while holding steady with the ensemble mean weight. Then days 7-8 Monday-Tuesday increased the means to 50-75 percent while phasing out the GFS by Tuesday. ...Weather/Hazards Highlights... The upper ridge settling over the mainland later in the week should promote a period of above normal temperatures, especially over much of the Interior. Increasing uncertainty over the strength/persistence of this ridge relative to an upper low farther north has lowered confidence in the duration of the warm anomalies, though for now the forecast reflects multiple days of above normal readings per recent consensus/continuity. A strong and persistent upper ridge would raise fire weather concerns with specifics depending on winds and moisture, as well as any scattered convection. Continue to monitor forecasts as important details of the pattern become better resolved. Some scattered areas of rainfall will be possible over southern areas and the North Slope/Brooks Range, with these regions plus parts of the Panhandle seeing pockets of below normal high temperatures. Greater influence of the northern upper low would lead to more precipitation coverage over parts of the northern mainland. The mean low near the Aleutians (composed of one or more separate systems) will likely support unsettled weather over the region for most of the period, with coverage and amounts of rainfall at any particular time depending on the exact shape/location of surface low pressure and upper dynamics. Rausch 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