Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 657 PM EST Tue Dec 24 2024 Valid 12Z Sat Dec 28 2024 - 12Z Wed Jan 01 2025 ...Arctic cold overspreads much of the Mainland with the coldest temperatures of the season for the western/central Interior... ...Gusty winds possible over parts of the Aleutians late week and possibly for Cook Inlet and surrounding areas next week... ...Overview with Guidance Evaluation and Preferences... The medium-range period will likely begin with an omega blocking pattern across the Alaskan domain while a deepening upper trough swings south from the Arctic Ocean toward the top edge of the omega block. Cyclonic circulations will tend to develop on either side of the omega block and then track along the Aleutians before occluding when they move toward the Gulf of Alaska. Ensemble means generally agree that the arctic trough will lift north and retreat into the Arctic Ocean from early to the middle of next week as a high pressure ridge from the omega block possibly evolves into a closed high to the northwest of Alaska. The ensemble means have been trending more pronounced regarding this evolution, with the EC ensemble means indicate the most pronounced solution. Meanwhile, the deterministic solutions have been most chaotic near/along the Aleutian storm track under this omega block. These solutions begin to diverge further on Day 5 (Sunday) as a triple-point low located just south of the central Aleutians is forecast to break off from the main cyclone farther west. The deterministic guidance then lifts the disturbance(s) to the north and east much faster into the Gulf of Alaska than what the ensemble means indicate. This is especially the case with the GFS solutions. The ECMWF and CMC solutions are much slower by Day 8. Prefer to stay closer toward the ensemble means especially for Days 7 and 8 as they yield solutions in reasonably good continuity from yesterday's Day 8 forecast. The WPC medium-range forecasts for Alaska were based on a consensus blend of 40% from the 06Z GFS/GEFS, 40% from the the 12Z ECMWF/00Z EC mean, and 20% from the CMC/CMC mean. This blend transitions heavily toward the ensemble means by Day 8 for the reasons noted previously. ...Weather/Hazards Highlights... A broad cyclonic circulation centered over the Gulf of Alaska will gradually weaken and dissipate early in the medium-range forecast period through this weekend. The precipitation along the southern coastline will continue to taper off. The next system tracking eastward into the Aleutians will bring the next round of generally light to moderate precipitation from west to east through the island chain for the entire medium-range period. The system could bring a threat of high winds for the western portion of the Aleutians this weekend as a triple-point low is forecast to develop just to the south. The low is forecast to broaden and intensify further as it head in the general direction of the Gulf of Alaska early next week and raise the threat of high winds from the Kenai Peninsula, across Cook Inlet toward the eastern Alaska Peninsula and possibly Kodiak Island. This system will likely increase precipitation chances along the southern coastlines but with only modest amounts in the forecast at this time. Meanwhile, a surge of arctic air is expected to overspread much of mainland Alaska from west to east during the forecast period under the passage of the upper trough from the Arctic. Temperatures are forecast to be around 20-35 degrees below average, with actual temperatures dipping well into the -30s in the northwestern Interior and North Slope, with -10s and -20s as far south as the lower Yukon and Kuskokwim over the weekend. Temperatures should slowly moderate first in western areas Monday and across most areas next Tuesday into Wednesday as the ridge aloft build in from the east. Across Southeast Alaska, temperatures will likely gradually cool from above normal this weekend to near normal or perhaps a few degrees below for highs as increasing easterly winds bring colder air from northwestern Canada toward the coast. Kong 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