Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
002 FXAK68 PAFC 210118 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 518 PM AKDT Thu Jun 20 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Tonight through Sunday)... 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 an east-west oriented upper trough lifting northward from the Gulf into Southcentral. Winds and rain are on the increase across the Gulf and Kodiak Island ahead of the low. Extensive cloud cover with the upper trough is leading to a cooler day along coastal areas of Southcentral from the Kenai Peninsula to Prince William Sound. However, there is very little in the way of precipitation, with just some patchy light rain along the immediate coastline. Meanwhile sunshine over interior Southcentral has led to increased instability ahead of the upper trough. As a result scattered showers and isolated thunderstorms have developed (as of mid afternoon) near the Wrangell Mountains, Alaska Range, and Talkeetna Mountains and are tracking roughly from ESE to WNW. The bulk of showers and thunderstorms will exit toward the Alaska Range this evening On Friday, the main upper trough from today will weaken and rotate northwestward toward Interior Alaska. Atmospheric flow over Southcentral will back around to the northeast in response to the Gulf low progressing eastward. 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 tomorrow 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 varies on the center of the ridge, with most guidance over the western Interior. This will bring even strong 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`s difficult to nail down the preferred areas for convection and overall storm motion. && .SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS (Days 1 through 3: This afternoon through Sunday afternoon)... 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. Diving into the details... the big eye-catcher will be the numerous showers and isolated to scattered thunderstorms moving across Southwest Alaska this afternoon and evening. While the forecast had been plagued by poor model agreement, models have steadily come into better agreement today, especially with the weak shortwave moving overhead that`s helping to spur on this convection. We`ll be keeping an eye on this convection through the overnight hours, but based on how the convection has developed so far, showers and thunderstorms could be moving west a bit more quickly than initially anticipated. This means that areas west of where thunderstorms are currently forecast, like Bethel, could see some lightning today and tonight. Storm motion will be east to west today, so if you see lightning and thunderstorms approaching from the east, be sure to stay weather aware as they could be moving into your location. Thunderstorm chances continue through the weekend, though forecast confidence decreases appreciably for Saturday and Sunday afternoon. Even for tomorrow afternoon, there is some forecast uncertainty based on how storms perform today. If clouds linger from today`s storms, that could affect daytime heating for tomorrow`s storms. Either way, expect storms to generally move from north to south both Friday and Saturday afternoons as steering flow aloft becomes more northerly. For mariners in Bristol Bay, this means that showers and thunderstorms could move off land and onto coastal waters, presenting a marine hazard. Stay tuned as we continue to refine this aspect of the forecast. Otherwise, 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. -KC && .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...Light and variable winds will become stronger out of the southeast by this evening as the winds out of the Turnagain Arm strengthen. Winds will eventually abate during the overnight hours. Showers and perhaps and isolated thunderstorm may develop in the general area (Talkeetnas, Chugach Mtns) on Friday, but will likely remain out of ANC. Otherwise, VFR conditions will prevail throughout the TAF period. && $$