Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
531 FXAK68 PAFC 191329 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 529 AM AKDT Thu Sep 19 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Saturday)... The powerful low that tracked across the southern potion of the state the past few days has now moved on shore and into Canada. The final impact from it around the Gulf is some sea heights which are still at small craft advisory levels today. With the next low southwest of Kodiak and looking to take a track across the far southern Gulf and then into the eastern Gulf, Southcentral is under some ridging today which has helped clear out skies from Kodiak through Cook Inlet and to Prince William Sound. These clear skies have dropped temperatures into the 30s in many locations that have not been that cold so far this season. However, all is not clear skies mostly due to the upper level pattern. The 500 mb trough associated with that strong low is near the AlCan border early this morning, and while it is moving eastward, another short wave can be seen on satellite moving through the northern Susitna Valley and into the Copper River Basin. While this short wave should mostly bring just some cloud cover to these areas today, a stronger wave will move into the Susitna Valley and to the Copper River Basin tonight into Friday. This wave will tap into some low level moisture from the Gulf and bring in some rain and snow showers tonight into Friday night for the Talkeetna Mountains southeastward into Prince William Sound as the Copper River Basin. This is where most of the forecast uncertainty lies for tonight into Saturday. Precipitation type is beginning to become more of a question this time of year and higher elevations along the highways, such as near Paxson and near Eureka may see the rain mixing with or turning to snow during the overnight hours. Any accumulations are expected to be light at this time, but it does bear watching. The Prince William SOund region will be all rain. How far east this wave dig will also make a big difference for whether Anchorage and the Matanuska Valley will showers along the mountains for Friday or if it will clear out Friday night into Saturday morning and bring below freezing temperatures to east Anchorage and colder areas such as Willow and the Butte. The western Kenai Peninsula should be mostly clear Friday night so Kenai, Soldotna, and other colder areas will likely get below freezing Friday night into Saturday morning. && .SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3)... Generally colder and quieter weather is on tap for most of the Bering Sea and Southwest Alaska as a ridge builds in over the Bering Sea. While dry weather and weak subsidence is likely for Southwest Alaska, there is a low potential for embedded shortwaves to bring brief periods of precipitation (rain, snow, or a mix) to the Kuskokwim Valley Friday through this weekend. This should be very minor and not widespread. Farther west, a front accompanying a Kamchatka low is lingering over the western Aleutians and western Bering Sea. Progression of the front is being suppressed by the ridge over the Bering Sea, keeping rainfall likely over the western Aleutians until Friday morning. South of the ridge along the Aleutian Chain, a surface low is moving eastward. Chances for rain showers could skirt the eastern Aleutians this morning, but models have continued to trend the low more south so little precipitation is expected. With the ridge in place and its strength dictating the synoptic flow, a series of troughs moving toward the Aleutians will be diverted to along this Aleutian track. The next low approaching the western Aleutians arrives tonight and deflects eastward, spreading precipitation to the central Aleutians before quickly dying off in the southern Bering Sea for Friday night. Yet another, stronger low tracks behind the previous for Saturday morning. Precipitation is likely for Saturday across much of the Aleutians. Models are in reasonably good agreement for the low center to track east along the Chain, reaching the Alaska Peninsula for Sunday and into the Gulf of Alaska by Monday. The Pribilof Islands should remain mostly dry until Saturday night when chances increase to around 30 to 40 percent. Precipitation on Sunday will depend on how quickly the former low dies off in the southern Bering and then also on the low center position of the weekend system shifting slightly north or south. Winds are expected to be stronger with this weekends low. Small craft winds increase to gales over the weekend near the eastern Aleutians and Alaska Peninsula. Storm force gusts out of the north and northwest are possible near Unalaska Sunday morning. rux && .LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)... The upper level Alaska Weather map shows a mildly cyclonic flow with a number of perturbations from Eastern Asia into Canada. These support surface lows and fronts that will sweep over the Aleutians and the Alaska Peninsula. These systems will become more or less stationary and weaken across the Northern Gulf of Alaska through the forecast period. A ridge over the Bering through Monday flattens out through midweek. The ECMWF is running more energetically with greater amplitude, so the GFS/Canadian models are preferred. Locally heavy rains spread from the Central Aleutians, over the AKPEN and Kodiak Island and across the Gulf through Monday. Locally heavy rains occur over the Southcentral coast, with lesser amounts pushing inland. The associated surface also brings near gale force winds with gale force gusts over the Southern Bering, diminishing Monday. Widespread gale force winds extend along the Pacific side of the Aleutians and AKPEN. The surface low continues into the Gulf just East of Kodiak Island, winds intensify to high end gales and storm force gusts. Worst conditions are expected through the Barren Island, lower Cook Inlet and Shelikof Strait Monday, diminishing Tuesday. A gale force barrier jet forms along the North Gulf Coast for Monday, diminishing late. - Kutz && .AVIATION... PANC...There is high confidence VFR conditions prevail to the weekend. There is a small chance for low-lying morning fog early this morning, but light winds mixing the boundary layer are making it more unlikely. && $$