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FXAK68 PAFC 230201 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 501 PM AKST Sun Dec 22 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Tonight through Wednesday)... Precipitation remains largely downsloped out this afternoon, with some breaks of low elevation sunshine being observed at some inland locations, including Anchorage. The pattern remains the same as the past several days, with low pressure tracking from the southern Gulf toward Kodiak Island and a series of shortwave troughs lifting north across Southcentral Alaska. Freezing rain, or meteorological rain with below-freezing surface temperatures, will continue to be a possibility at times for many locations across Southcentral through Monday night. Snow will be limited to elevations above 2000-3000 ft, with the exception of the potential for an inch or so of snow accumulation in the western Copper River Basin near Eureka and Tahneta Pass this evening as cold northeasterly flow leads to some upslope precipitation for parts of the Copper River Basin. Greater snow accumulations (up to around 4 inches) are likely along the Richardson Highway south of Tonsina, though this will be mixed with up to a tenth of an inch of freezing rain. Along the Edgerton Highway, sleet is expected to mix with snow as warm air is in place across the southern Copper Basin while a deep layer of cold air remains near the surface. Monday morning, the main axis of the upper level trough shifts north across Southcentral, bringing the next significant chance of precipitation spreading inland past the coastal mountains. The Copper River Valley can be expected to get in on the action as it looks like a small amount of snow (less than one inch) will be able to accumulate in the valley. However, there is significant uncertainty with what this will do for portions of the southern Copper Basin, where some model guidance suggests the push of southeasterly winds, which are expected to reach the surface, bring temperatures above freezing for some time. More likely, though, the depth of antecedent cold air will prevent temperatures from warming that significantly and instead peak somewhere in the 20s. A shallowing of the cold air near the surface will thus make freezing rain a possibility during this round of precipitation on Monday. For the Cook Inlet region, the Anchorage Bowl and the southern Susitna Valley are the most likely focus for freezing rain potential. Though this would likely be only a brief period for Anchorage, there is a greater chance of accumulating precipitation in the Susitna Valley, particularly south of Willow, however not all models are biting off on that solution just yet. For the Kenai Peninsula, warmer temperatures will keep any precipitation rain, and the Matanuska Valley looks to stay mostly dry. The southerly push of warmer air also coincides with a weakening down-inlet pressure gradient, which will allow for a straightening of the Turnagain Arm wind, likely impinging on the south side of Anchorage for a time on Monday afternoon, which could bring temperatures locally close to 40. However, cooler air begins to move in aloft on Monday night, and though surface temperatures may remain above freezing for a time precipitation changes over to all rain or snow, and freezing rain becomes less of a concern across Southcentral. Tuesday and Wednesday, shortwaves continue to lift across the area, though downsloping remains, so expect continued wet conditions along the coast and periods of very light rain/snow inland. Quesada && .SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3: Through Wednesday)... Additional precipitation will still be possible across the greater Bristol Bay region, tonight into Monday. A warm layer of air between freezing layers aloft and at the surface, will provide a favorable setup for freezing rain, with the best chance for up to a tenth of an inch of freezing rain between Koliganek and Dillingham. A Winter Weather Advisory has been issued through Monday morning due to this potential. The entire column will cool below freezing by Monday afternoon, allowing any lingering pockets of freezing rain to switch over to snow. The low which brought freezing rain and mixed rain/snow to Southwest Alaska over the previous several days has weakened north of Cold Bay. This will consolidate Sunday night over Kodiak Island with a low in the northern Gulf. Meanwhile, the front of a strong North Pacific system will sweep eastward across the the Aleutian Island chain Monday. Storm force winds will initially be possible as the front reaches the Western Aleutians, but the front should quickly weaken to gale force before it lifts northeast into the southern Bering Monday afternoon. Models continue to struggle to resolve rapid formation and dissipation of multiple triple-point lows along this front, and there may be changes to the wind and precipitation forecast for Monday into Tuesday due to this inherent uncertainty for the location and development of these smaller lows. There is a general consensus for the main low to eventually shift or redevelop towards the AKPen by Tuesday afternoon. Strong northeast winds will also continue to spread across the Bering Sea as a colder air mass begins to spread south from the Arctic Tuesday night into Wednesday. && .LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)... A broad upper level trough stretches from the Arctic all the way down to the North Pacific and northern Gulf on Wednesday, with several surface lows forming in the pattern. The trough axis will shift eastward into the weekend, with the main cluster of surface lows taking shape in the central Gulf. A ridge will start moving into the western Bering late Thursday before moving over mainland Alaska by late Saturday. Behind the ridge will be a second upper level trough moving in from Kamchatka over the western Aleutians and Bering by Saturday. The Bering ridge and a ridge forming over Southeast Alaska will interact over the interior on Sunday, resulting in a strong ridging pattern over most of mainland Alaska by the end of the extended forecast period. While the troughing pattern persists through Saturday, the series of lows and fronts forming near the Alaska Peninsula, Eastern Aleutians, and Kodiak will help provide repeated rounds of heavy rains along the coastline until the ridge builds in. Bitter cold air will begin to fill in over interior Southwest Saturday before spreading into portions of Southcentral on Sunday, continuing beyond the end of the extended forecast period. &&.AVIATION... PANC...VFR conditions with light northerly winds will persist through Monday morning. There remains a slight chance this evening of some very light sprinkles of rain over the terminal. The next shortwave and surface trough will move across the Anchorage Bowl early Monday morning. These will bring a better chance for precipitation to the terminal early Monday morning through midday. With temperatures hovering near freezing, the precipitation may fall as a period of freezing rain. Any ice accumulation is expected to be light, nothing more than a glaze of ice. The upper-level wave will also bing an increase in southeasterly winds at mountaintop level and through Turnagain Arm. This will likely result in a period of LLWS Monday morning. By midday, there is a chance that the southeasterly Turnagain Arm wind lifts into west Anchorage and across the terminal. Any southeasterly wind over the terminal will likely become northerly again by Monday evening. && $$Fetched URL: http://tgftp.nws.noaa.gov/data/raw/fx/fxak68.pafc.afd.afc.txt
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