Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 755 PM EDT Thu Oct 26 2023 Valid 12Z Mon Oct 30 2023 - 12Z Fri Nov 03 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 potentially across much of the 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... Model guidance remains agreeable with the existence of a closed upper low atop the Bering Sea to start the workweek, but the track remains a questionable aspect of the forecast. Models agree better today that some energy should spill southward into the northern Pacific south of the Aleutians to form a closed low there even as the period begins Monday, much like the non-NCEP guidance yesterday. So the forecast trended that direction, but the remaining Bering low still has spread similar to yesterday's guidance, with the CMC and UKMET tracking it north quickly. The 12Z GFS showed a westward movement with the low, unlike anything else, so favored the 06Z run for that feature instead. Generally the 12Z ECMWF and the GEFS and EC ensemble means seemed to be the best consensus position. Another upper low atop the Kamchatka Peninsula shows a general track southeast and then east in the guidance. The 06Z GFS was slower than consensus with this low, however. By the latter half of the week it becomes quite questionable how the upper lows in the northern Pacific could interact. These differences affect the strength and track of surface lows, including one tracking near 40N through the week that could strengthen considerably if it interacts with the upper-level energy. While there should be mean low pressure in the northern Pacific, the details have low confidence at this point. Then there remains potential for the southern side of an Arctic trough/low to come into at least the northern Mainland along with an associated surface front, serving to help erode the ridge. There is uncertainty with how far this could press into the state, with the ECMWF lingering it north. For the WPC forecast, the CMC and UKMET were used only minimally with more favoring toward the ECMWF and 06/12Z 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 precipitation near the eastern side of the Alaska Peninsula into the Kenai Peninsula and Southcentral Alaska through Monday, with some lingering lighter amounts possible as the week progresses. There is quite a bit of uncertainty in timing and amounts of precipitation given the spread with upper and surface low positions. But Southeast Alaska could see increasing chances for generally light precipitation by midweek and beyond dependent on the interaction of an upper low with the ridge. The western Mainland could see some rain and/or snow coming in for the first half of a week as a front may come into the region. 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 through much of the week. Though as the upper ridge gets suppressed, temperatures are likely to moderate closer to normal. The primary exception of the milder than normal temperatures will be across Southeast Alaska which could be cooler than normal, but with gradual moderation toward normal by mid- to late week. 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