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Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
310 FXAK68 PAFC 211256 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 456 AM AKDT Fri Jun 21 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Friday through Sunday)... No significant changes to the previous discussion... Key Messages: * Warmer temperatures and an increase in thunderstorm activity coming to Southcentral this weekend. * Gusty offshore winds in Resurrection Bay and Passage Canal Friday night through Saturday morning. * Gusty northerly winds across the northern Susitna Valley and northern Copper River Basin on Friday night through Saturday. Looking at satellite imagery, the key weather features are a vertically stacked low in the northeast Pacific tracking into the Gulf of Alaska and a north-south oriented upper trough stalling over the Southwest Alaska coast. A second wave is situated along the Alaska-Canada border, just north of the Alaska Range. The bulk of the shower and thunderstorm activity has diminished overnight and remains focused along both the trough over Southwest and underneath the Al-Can wave. Today, the atmospheric flow over Southcentral will back around to the northeast in response to the Gulf low progressing eastward and the upper trough over Southwest rotating northwestward. Clouds will diminish along the coast, while the northerly component to low level flow results in warming temperatures and establishment of a thermal trough over interior Southcentral. This will result in an uptick in showers and thunderstorms this afternoon and evening, though the bulk of them will remain inland. Storm motion will generally be from northeast to southwest. Continuing to Saturday, an upper level ridge will strengthen somewhere over the Alaska Interior. Model guidance continues to vary on the center of the ridge, with most guidance placing the center over the western Interior. This will bring even stronger northerly flow to Southcentral Friday night through Saturday, leading to additional warming and destabilization of the atmosphere. Locally gusty offshore winds are expected along the coast and along the Alaska Range into the Susitna Valley and Copper River Basin, contributing to very warm and dry conditions region-wide (probably not quite as hot as last Saturday, but not too far away). Showers and thunderstorms will form inland and track toward the coast the late afternoon and evening hours, potentially including Anchorage once again. While Sunday continues to look warm with afternoon/evening showers and thunderstorms, there is quite a bit of model spread in location of upper ridging and troughs. Thus, it difficult to nail down the preferred areas for convection and overall storm motion. -SEB/TM && .SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS (Days 1 through 3: Friday morning through Monday morning)... The big picture of the forecast remains largely unchanged, though there have been major updates to the precipitation and thunderstorm forecast for Southwest Alaska as we continue to assess more data. Expect thunderstorm chances to persist through the weekend for Southwest Alaska, along with a general warming and drying trend. For the Bering Sea and Aleutian Islands, most areas will see light winds less than 25 kt as the ridge moves east across the Bering Sea, and incoming lows remain on the periphery of the forecast area. This morning, showers move offshore from the Kuskokwim Delta and south to the Alaska Peninsula by this afternoon. Thunderstorm chances for mainland Southwest continue through the weekend, though forecast confidence decreases appreciably for Saturday and Sunday afternoon. Expect storms to generally move from north to south both Friday and Saturday afternoons as steering flow aloft becomes more northerly. Shower coverage gradually diminishes this weekend as the upper level ridge moves in. Afternoon and evening highs will climb into the 70s under this ridge, with the potential for temperatures to even approach 80 on Monday. && .LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)... A number of changes come to light on the Alaska Weather map through the forecast period. The upper level low over the Russian Far East curves towards the Sea of Okhotsk and dissipates late Tuesday. Its extended trough forms another low over the Western Aleutians and Bering for Wednesday, and moving to the Central Bering for Thursday. A third low in the Eastern North Pacific exits along the Canadian coast for Thursday. A shortwave ridge over the Eastern Aleutians and Bering moves over Southcentral Alaska and reinforces an Interior ridge through Thursday. Model agreement in the geographic broad brush is good, but becomes somewhat chaotic in the finer details. ECMWF/GFS are closest in the details, the Canadian model runs low and slow. A well developed low and front spreads locally heavy rain and gusty surface winds less than gale force across the Aleutians and Bering, impacting the Pribilofs and Eastern Aleutians for midday Tuesday, and into Western Alaska, the Alaska Peninsula and Kodiak Island through Thursday. Surface thermal troughs support some convection across the Southcentral Interior South of the Alaska Range. Areas closer to the coast will see isolated to scattered showers through Thursday. -Kutz && .AVIATION... PANC...VFR conditions will persist through the TAF period. Light and variable winds this morning will turn more westerly by mid- day today as the sea breeze kicks in coincident with day-time heating. The terminal should stay dry today with convection staying further to the north over the Talkeetna Mountains and Chugach Mountains. Southwesterly winds will turn more light and variable overnight tonight into Saturday morning. && $$