Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 758 PM EDT Wed Oct 25 2023 Valid 12Z Sun Oct 29 2023 - 12Z Thu Nov 02 2023 ...Overview... Eastern Pacific/western Canada upper ridging will extend northward across much of Alaska into next week, causing much above average temperatures while gradually weakening. Meanwhile mean troughing will be in place atop the Bering Sea as an upper low starts off there early in the week but with some question on its eventual track, and another upper low tracks southeast from the Kamchatka Peninsula. The upper trough to ridge pattern will draw in moisture to the Alaska Peninsula and Southcentral Alaska for some enhanced precipitation early in the week, with some precipitation migrating to Southeast Alaska as the week progresses. An Arctic shortwave may track around the top of the ridge to bring a surface front across at least the northeastern Mainland. Temperatures could stay above average but somewhat moderated from the early week temperatures, though the Panhandle may stay on the cool side throughout next week. ...Guidance Evaluation and Preferences... The Bering Sea upper low's track looks to be the most questionable part of the forecast. Even by Day 5/Monday, models diverge on its track as energy within the trough may split. The ECMWF, CMC, and UKMET all split the energy with some tracking south into the northern Pacific and some tracking north. One difference though is that the CMC and UKMET are stronger with the northern energy and thus have a notable upper low feature moving into Siberia unlike the GFS, ECWMF, and the ensemble means. The ECMWF looks to show a better low position more in line with consensus in the Bering. The GFS runs have been showing that the upper low may stay consolidated, with a slow drift of the one upper low south and then east. The GEFS mean generally follows a southern position, while the EC ensemble mean is farther north more like the deterministic ECMWF, though both means are not as extreme. How much energy presses south into the northern Pacific will help determine reorientation/erosion of the ridge to its east as well, so this will continue to be monitored. Other features of note include potential for the southern side of an Arctic trough/low to come into the northern Mainland along with an associated surface front, and another upper low tracking southeast from the Kamchatka Peninsula. With the former, the more favored GFS/ECMWF indicate a trend today toward having the shortwave/front coming into the Mainland. With the latter, model guidance is in fair agreement with the track but with some north/south spread (ECMWF farther north than the GFS and CMC) and some spread in its strength. These differences also affect the strength of a surface low tracking across 40N through the week that could strengthen considerably if it interacts with the upper-level energy, which the 12Z GFS is indicating. Certainly did not feel comfortable going that strong at this point. For the WPC forecast, the CMC and UKMET were used only minimally with more favoring toward the ECMWF and GFS. Increased the proportion of the GEFS and EC ensemble means as the forecast progressed, to half by Day 7 and over half by Day 8. ...Weather and Hazards Highlights... The forecast pattern should favor the best moisture focus and locally moderate to heavy precipitation from the Alaska Peninsula Sunday, with some precipitation of varying types extending northward across the western mainland. The enhanced precipitation amounts will move into Southcentral Alaska and the Kenai Peninsula through the first half of next week. A general shift of the precipitation shield from west to east looks likely, but there is quite a bit of uncertainty in timing and amounts of precipitation shifting into the southeastern Mainland into the Panhandle, dependent on the upper low/ridge interaction. Farther north, some of the western mainland moisture could interact with a front reaching the North Slope to produce mostly light snow around early next week. Much of the state will see above normal temperatures throughout the forecast period. The greatest anomalies will be across the North Slope and northwestern Mainland early in the week, with lows 20-40F above average and highs more along the lines of 10-20F above normal expanding eastward into the workweek. The primary exception will be below average temperatures across Southeast Alaska, which could see some gradual moderation closer to normal through midweek. Tate 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