Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Mon May 22 2023 Valid 12Z Fri May 26 2023 - 12Z Tue May 30 2023 ...Overview... Latest guidance continues to show a favorable setup for some enhanced rainfall/high elevation snow along and near the southern coast into the Panhandle during the period, from a combination of an initial southern coast into northeastern Pacific upper trough (likely containing an embedded low) and then steady progression of a Bering Sea system into the Gulf of Alaska. Some details of the supporting evolution still need to be resolved though. Meanwhile the models and ensembles have been quite varied over recent days regarding flow aloft farther north over the mainland and Arctic, with individual solutions varying among a modest north-south trough/weakness, east-west ridging, or a col region depending on the day. ...Guidance Evaluation/Preferences... Recent ECMWF runs and the 12Z CMC were closest to the ensemble means in principle for the evolution of the initial southern coast into northeastern Pacific upper trough, likely containing an embedded low near or a little southeast of the Kenai Peninsula as of early day 4 Friday. 06Z/12Z GFS runs held the feature a little farther southwest of this majority initially and remained slowest with its northeastward progression and opening up by day 5 Saturday, leading to a longer duration of enhanced precipitation than suggested by most other guidance. The new 18Z GFS has trended somewhat toward the favored majority scenario. The guidance average has been trending faster to bring the Bering Sea system eastward into the Gulf of Alaska, with this trend particularly noticeable after Saturday. There has been a modest southward trend as well, though preference was not to adjust as far south as the GFS/UKMET that occupy the most southern side of the envelope in light of the 12Z CMC mean that actually adjusted northward from its prior run. Greater emphasis on recent ECMWF runs and an average of the GEFS/ECMWF means seemed to provide the best intermediate solution while reflecting latest trends. To the north of the above two systems, guidance spread and run-to-run variability keep confidence low for the shape of flow aloft across the northern half of the mainland and Arctic. There is some persistence in the idea of east-west ridging across the northern mainland to start the period on Friday but then solutions diverge into different depictions of weak troughing (possibly extending south from fairly progressive Arctic mean flow) or a col. In general recent GFS runs have been on the more extreme side of the spread in terms of how much east-west ridging they develop over the mainland during at least portions of the first half of next week. Based on the above considerations, today's forecast started the first half of the period with a blend of half ECMWF (split between the 00Z and 12Z runs), a small 12Z GFS component to counterbalance the ECMWF a bit in some areas, and 30 percent total means (12Z GEFS/00Z ECens). With confidence in specifics declining further after mid-period, the blend increased ensemble mean weight to 50 percent with the remainder composed of the operational runs to enhance detail versus the means where possible. ...Sensible Weather and Potential Hazards... As of the start of the period early Friday, expect precipitation across the southern coast and Panhandle to be ongoing in association with the initial southern coast/northeastern Pacific upper trough and associated surface reflection. Highest totals may be just before the start of the forecast period, with intensity decreasing through Friday as the upper system beginning to open up. At the same time, the system over the Bering Sea (with a surrounding area of brisk winds late this week) will spread precipitation across the eastern Aleutians/Alaska Peninsula late this week, followed by potential enhancement over some locations along the eastern Alaska Peninsula and points eastward during the weekend with a triple point wave that may track near Kodiak Island before heading into the Gulf of Alaska. Persistence of rain/higher elevation snow during the first part of next week will be sensitive to the exact track of this wave. Some areas of precipitation will be possible over other parts of the mainland late week into the weekend due to the energy ejecting from the initial southern coast/northeastern Pacific system. Then coverage and amounts over the central/northern mainland will depend in part on uncertain details of flow aloft. The majority of the state will likely see below normal high temperatures during the period, with coolest anomalies likely to be across southern areas. The far northwestern corner of the mainland may have the best chance for above normal highs late this week into the weekend. Anomalies should be warmer for low temperatures, with a mix of readings above or below climatology. Along with the precipitation forecast, uncertainty with details of flow aloft also tempers confidence in temperatures over the northern half of the mainland by the latter half of the period. 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 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