Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 730 PM EDT Thu Oct 31 2024 Valid 12Z Mon Nov 04 2024 - 12Z Fri Nov 08 2024 ...Deep low pressure system(s) could cause high winds across the Aleutians/Alaska Peninsula and southwest Mainland and enhanced precipitation in southern Alaska next week... ...Overview... A quick-moving shortwave trough and surface low moving across Haida Gwaii could bring some precipitation to the southern Panhandle as the period begins Monday. Meanwhile farther west, models continue to indicate that an upper low will move across the Bering Sea and vicinity and support consolidating and deepening surface low pressure formed in part by what is currently Tropical Storm Kong-rey in the western Pacific. The surface low is forecast to move from the northern Pacific, cross the eastern Aleutians/western Alaska Peninsula, and reach Bristol Bay to the Lower Kuskokwim/Yukon regions Tuesday-Wednesday, bringing high winds there and heavy precipitation potential to its east across Southcentral to Southeast. Additional energy and another surface low are likely to move through the Aleutians eastward and reinforce the trough pattern. This deepening and then reloading upper troughing over the Bering Sea southward into the Aleutians and northern Pacific should promote ridging developing across the eastern Mainland to Panhandle for mid- to late week. ...Guidance Evaluation/Preferences... 12Z model guidance showed relatively minor placement/timing and strength differences with the surface low moving through Haida Gwaii Monday, after the 06Z GFS seemed slow. Then attention turns to the notable low moving northeast in the North Pacific nearing the state. Some models over the past day or two have shown multiple surface lows through Monday, with questions of which one will dominate before consolidating by Tuesday. Today's 12Z guidance tends to prefer deepening the low farther northeast, which EC runs have been persistent with. The 12Z GFS still does have two surface lows but ends up pretty agreeable with the EC. But the CMC has two surface lows that are displaced from other guidance, ending up farther southeast and tracking toward Kodiak Island, supported by a farther east upper low compared to consensus. Thus did not prefer the CMC today. Models are generally in the 940s or 950s with the low at peak depth. The upper low is forecast to meander into midweek with some question of whether the surface low moves north or east as it weakens. All this will be affected by an upstream system tracking east across the Aleutians and vicinity and approaching Wednesday-Thursday. The general theme is that vorticity could combine with the upper low already in place on its southern side and pivot it slowly east. A surface low associated with it shows significant spread by Wednesday though. Ensemble means were quite agreeable in showing a low track across the Aleutians with similar timing, but individual models had quite a bit of spread. Most deterministic solutions were faster and farther south into the North Pacific with this low track, with the 12Z GFS particularly far south and weaker. Interestingly the CMC, not favored for the first low, clustered the best with the ensemble means with the second low. The 12Z EC mean that was not available at forecast generation time did trend a bit farther south/east. Leaned toward the ensemble mean low positions rather than deterministic models for this feature. Overall the WPC forecast favored a GFS/ECMWF blend with lesser components of other models/means early in the period. Gradually transitioned toward more ensemble means, reaching half by Day 6 and more Day 7-8 given the increasing spread. ...Weather/Hazards Highlights... Brief moderate to heavy rain is possible in the southern Panhandle on Monday with the Haida Gwaii low. Then the deepening surface low moving from the northern Pacific northeastward is likely to cause high winds for the Aleutians and Alaska Peninsula on Monday and moving into the Lower Kuskokwim and Lower Yukon regions given the strength of the low. Ahead of the low, precipitation will spread from the Alaska Peninsula and into the Southwest Mainland Monday, to Southcentral on Tuesday and toward Southeast by Wednesday. The reloading upper low pattern should promote additional rounds of precipitation across southern Alaska into late next week. Currently the heaviest precipitation amounts are forecast from the Kenai Peninsula into Southeast on Tuesday, where the hazard is located on the Day 3-7 Hazards chart. Meanwhile, rounds of snow showers are possible farther north through the period. A tight pressure gradient across the North Slope could also cause some breezy easterly winds and blowing snow there. Most locations will see above average temperatures rising further next week, with the possible exceptions of the Seward Peninsula, parts of the higher mountain peaks, and the Panhandle showing cooler temperatures early in the week. In most cases the anomalies for morning lows should be greater than anomalies for daytime highs. High temperatures will generally be in the upper teens to 20s in the Interior and North Slope, with 30s and low to mid 40s in southern areas. 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