Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
146 FXAK68 PAFC 190115 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 515 PM AKDT Wed Sep 18 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: This afternoon through Saturday evening)... Pockets of heavier shower activity across the Northern Gulf Coast this afternoon continues to slide farther east to the Panhandle tonight as the North Gulf Coast and Prince William Sound begin to clear out. The low pressure system causing this disturbed weather will also continue moving east through the Gulf towards the Panhandle. Flow behind this low will continue to be off-shore in nature and gusty at times for areas like Seward, Whittier, and Kodiak with the north and westerly winds. With cold air banking up in Kamishak Gap, also expecting some gale-force winds through the Barren Islands tonight and into the day on Thursday before the cold air and westerly flow weaken later in the day. While there maybe some sunshine tomorrow across most of Southcentral Alaska, it is not expected to be widespread, but more breaks of sunshine in between cloudy periods. This is due mostly to continued cyclonic flow and weak upper-level shortwaves moves through the progressive west-to-east flow. One such shortwave looks to dig southward across much of the central interior and into Southcentral Thursday night and Friday. This could provide the chance at a few showers across the Susitna Valley and Copper River Basin. Although a few snow showers or rain/snow showers mix could be possible in the Copper River Basin late Thursday night into early Friday morning, and again Friday night into Saturday morning, it remains unseen if the area can cool down enough at the surface due to the impending cloud cover associated with the upper waves. The best chance of seeing a little mix would be around the Eureka area. Otherwise, most wintry precipitation should be confined over the mountains. Additional waves also look to traverse the Gulf from west-to-east keeping the Northern Gulf Coast and Prince William Sound unsettled and showery Friday into Saturday. Also of note, the same guidance trends exhibited with the North Pacific low yesterday were also exhibited today. The current trend is for the system to stay mostly to the south of the area and affect mostly Southeast Alaska Friday and Saturday. The Canadian guidance continues to be the northern outlier as this forecast package continues to depict a more southern solution and in line with the majority of guidance. Aside from the cloudiness of the coast for late week into the weekend, cloudy conditions are also likely for most other locations across Southcentral due to the influence of upper-level waves moving through the area. Most shower activity should be confined to the Susitna Valley and Copper River Basin through Saturday evening. && .SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3: This afternoon through Saturday afternoon)... While stronger winds and showers will linger along Bristol Bay and the Alaska Peninsula through early tomorrow morning, generally colder and quieter weather is on tap as a ridge builds in over the Bering Sea. With light onshore flow and pressure building, it is possible that the Kuskokwim Delta, Bristol Bay, and Alaska Peninsula could have patchy fog tomorrow morning. While 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 Southwest Alaska Friday and this weekend. This should be very minor and not widespread. Farther west, a front accompanying a Kamchatka low is expected to move into the western Aleutians by this afternoon. The ridge will help slow the front`s progression, keeping rain chances likely for the western Aleutians and much lower elsewhere. One major change since yesterday`s forecast package is a shift in the track of a North Pacific low. Where previous model runs had shown this low remaining further south, more recent model runs have shifted it north, bringing small craft winds towards the Aleutian Islands and increasing rain chances from late tonight through tomorrow evening. Also by Thursday night, a low moves towards the Western Bering Sea and Aleutians. There may still be shifts in this low`s track, but generally expect winds primarily to small craft speeds with gales possible for the Western and Central Aleutians/Bering Sea. Currently, the forecast has this low stalling out near the Eastern Aleutians Friday night as it runs up against the ridge. We`ll see how models evolve their depiction of the forecast but, for now, the positioning of the ridge over the Eastern Bering Sea and Southwest Alaska will keep calmer, colder, and drier weather over these locations while directing incoming storms towards the Aleutian Islands, keeping this region wetter and warmer for the coming days. rux/chen && .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...An upper level low sits just east of the terminal this afternoon ans is continuing to move quickly to the east. There is high confidence that primarily VFR conditions should prevail as weak cyclonic flow comes through Anchorage through Thursday afternoon, bringing some light northwest to southwest winds. A brief shower is possible later this afternoon into early evening due to a weak upper-level wave dropping southeast through the Susitna Valley. There is a small chance that the lower atmosphere is moist enough to result in some low-lying fog tonight into Thursday morning, but the combination of light winds keeping the boundary layer mixed and the presence of clouds limiting radiative cooling makes it not very likely. Overall, things are looking good for a brief break in significant weather from Wednesday evening through Thursday, keeping VFR conditions through this time frame. && $$