Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 630 PM EST Sun Dec 22 2024 Valid 12Z Thu Dec 26 2024 - 12Z Mon Dec 30 2024 ...Bitter cold likely across much of the Mainland, the coldest temperatures of the season for the western/central Interior... ...Overview... An upper trough stemming from an Arctic to Chukchi Sea upper low phasing with preexisting energy along the southern coast to northern Pacific will lead to much colder temperatures across much of the state later this week into early next week as it slowly traverses east. Some precipitation is forecast ahead of this trough, with moderate to locally heavy amounts along the southern coast and light snow for the Interior. Upstream, an upper low will spin near the western Aleutians next weekend into early next week and support a couple of surface low pressure/frontal systems, bringing some precipitation and gusty winds to the Aleutians and Alaska Peninsula. ...Guidance Evaluation and Preferences... Model guidance shows rather good agreement on the large scale pattern described above through much of the forecast period, with smaller scale differences of surface low positions and energies aloft taken care of by a multi-model blend. Relatively larger model differences come into play early next week, as there is some spread with a ridge axis in between the Mainland trough and western Aleutians upper low. The ridge is set to traverse the Aleutians west to east Thursday-Saturday, but upper troughing in the northern Pacific already and perhaps another round of energy tracking south of the Aleutians serves to reorient the ridge with some models closing it off into an upper high. Even the ensemble means show some spread, with the 00Z EC ensemble mean over the southwestern Mainland while the 12Z GEFS mean is over the eastern Bering Sea with a stronger ridge axis. The newer 12Z ECens mean did nudge a bit west and strengthen so perhaps guidance is becoming more agreeable. The WPC forecast used a blend of the deterministic models early in the forecast period. Better than normal model consensus meant a majority of deterministic models could be maintained throughout the extended period, with some incorporation of the GEFS and EC ensemble means. ...Weather/Hazards Highlights... Surface lows in the Gulf of Alaska and vicinity, along with energy aloft and moist inflow ahead of the main trough, will bring some precipitation to the southern coast late week. Moderate to locally heavy totals are possible across Southcentral and Southeast Alaska, with multiple rounds of precipitation in some areas. Precipitation amounts should decrease into next weekend as the surface lows weaken. Farther north, some light snow is forecast to linger into Thursday (after moderate amounts midweek), stretching from the Y-K Delta northeast into communities like Galena and Bettles and affecting parts of the Dalton Highway. Snow chances will get pushed eastward later in the week as the upper trough brings in much colder and drier air to western Alaska. Northerly winds with this upper trough could produce gap winds in favored areas of the eastern Aleutians/Alaska Peninsula Friday-Saturday; models suggest a magnitude of around 30 knots for these winds. Then with surface systems tracking across the Aleutians, light to moderate precipitation and gusty southerly winds are possible for the weekend into early next week there. Significantly colder temperatures are likely across the state during the extended period given the upper trough. The cold will affect western Alaska Thursday-Friday, gradually push into central Alaska by Saturday, and across the rest of the Mainland next Sunday-Monday. Temperatures are forecast to be around 20-35 degrees below average, with actual temperatures dipping into the -30s in the northwestern Interior and North Slope and -10s and -20s as far south as the Lower Yukon and Kuskokwim over the weekend. Temperatures should slowly moderate in western areas early next week as the ridge aloft comes in, but may be slower to warm up than the upper ridge alone would allow because of a persistent cold surface high. Into Southeast Alaska, temperatures look to gradually cool from above normal late this week to near normal or perhaps a few degrees below for highs. Tate Additional 3-7 Day Hazard Information can be found on the WPC medium range hazards outlook chart at: The WPC Hazards Outline depicts these threats. 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