Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Sat Aug 19 2023 Valid 12Z Wed Aug 23 2023 - 12Z Sun Aug 27 2023 ...Wet pattern for much of the state with low pressure systems and Bering Sea troughing pulling in moisture... ...Overview... An Arctic upper low looks to track eastward north of the state around midweek, supporting a frontal system pushing into northern Alaska. But the main impactful part of the pattern will be upper troughing developing and getting reinforced over the Bering Sea through much of the week into the weekend, with likely two surface lows tracking northeastward across the Aleutians into the Bering Sea and the western Mainland, one during the latter half of the workweek and one Friday into next weekend. These lows and the mean moist southwesterly flow will provide increased rain chances across much of the state, generally spreading west to east in a couple of rounds. Downstream, Southeast Alaska should see ridging overhead for comparatively drier and warmer conditions. ...Guidance Evaluation/Preferences... Model guidance is reasonably agreeable with the Arctic upper low, though with the CMC a bit south and east of consensus. Guidance is quite agreeable that an upper trough axis will be in place over the Bering Sea at the start of the period midweek, with some slight shift eastward toward the state by Thursday-Friday. Some model guidance does show energy and troughing pressing farther east across the Interior by then, including the 12Z UKMET and the older 00Z ECMWF, but the larger cluster of the 12Z ECMWF/GFS/CMC holds it back, which also seems to be better supported by the ensemble means. This pattern will support a surface low moving north-northeast through the eastern side of the trough, starting just south of the Aleutians on Wednesday and into the Bering and perhaps along the west coast of Alaska Thursday-Friday. The CMC was somewhat farther east with its low track compared to consensus. Thus the initial forecast blend favored mainly the 12Z ECMWF and GFS with some lesser incorporation of the CMC and of the EC ensemble mean. Into the weekend, greater differences start to arise with energies coming from the north and/or west that could combine with the trough or push it east. Generally the ensemble means show the trough staying put over the Bering Sea/western Alaska, which among the 12Z operational guidance seemed most like the GFS. Despite some timing and placement differences, there is a good signal for another surface low with a similar track as the aforementioned one, but on Friday-Sunday. For the latter part of the period, quickly ramped up the proportion of the more agreeable GEFS and EC ensemble means to half day 7 and 70 percent day 8 given the deterministic model differences. ...Weather/Hazards Highlights... Lingering moisture and a frontal system in place across northern Alaska on Wednesday could lead to some slightly enhanced rainfall totals over the Brooks Range, particularly the western part. Meanwhile areas of the Alaska Peninsula should see increasing rain chances and amounts midweek, which will spread north and east through late week with the track of the surface low. Precipitation totals are looking highest in areas of terrain/upslope flow, like the Alaska Range and Southcentral, with the Brooks Range seeing some enhancement too. Snow is possible in the highest elevations of the mountains. The second surface low should spread another round of rain to the Aleutians/Alaska Peninsula around Friday and support continued precipitation across the Mainland through the weekend. Southeast Alaska is likely to be a drier area with just a few showers there through much of the period. The Brooks Range to North Slope should see the greatest negative anomalies for high temperatures during the period, though the coastal communities may stay closer to average. The eastern interior and southern Panhandle will see the best potential for above normal highs. Low temperatures look to be more above normal, though with the possible exception of the Seward Peninsula and northwestern Mainland. Tate 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