Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
992 FXAK68 PAFC 071327 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 527 AM AKDT Fri Jun 7 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Sunday night)... A large closed upper low centered overhead of the Eastern Aleutians (Dutch Harbor) this morning serves as the anchor for a long-wave trough over Alaska and the North Pacific. A few weak short-waves embedded in the extremely large cyclonic flow around this low are traversing Southcentral this morning, leading to some localized areas of showers, most notable a line of persistent training showers from Whittier to Portage and east Turnagain Arm. Partial clearing has occurred over inland valleys. Temperatures have cooled into the mid 30s to mid 40s, reflective of the cooler air mass in place at the moment. Gap winds, which were quite strong on Wednesday, have largely diminished, though the Turnagain Arm wind into Anchorage International is lingering. The most eye-catching feature in satellite imagery is a deep vertically stacked low over the northeast Pacific (centered near 45N 146W as of 5am). The development of this low has resulted in amplification of the flow in the NE Pacific with a ridge building out ahead of it off the NW CONUS coast on up to the eastern Gulf and SE Alaska. This in turn has led to a strengthening southerly jet streak, which is helping to transport warm moist air north- northwestward, well out ahead of the low. This atmospheric river will head right for Kodiak later today and then continue westward across the Alaska Peninsula into Bristol Bay, as it gets absorbed into the flow around the Aleutian low. This is setting up to be multiple days of moderate to heavy rainfall for Kodiak Island, beginning later today and continuing through Sunday night. This first storm looks the most impressive, with abundant moisture, strong dynamical lift, and strong low level winds and resultant upslope flow. As a result, Kodiak City and the east side of the island will see particularly heavy rain tonight through Saturday. There may then be a very brief break (where rain will at least lighten up). However, a large cyclonic gyre will take shape Saturday, with multiple strong short-waves/upper lows rotating around the North-Central Pacific to the western Gulf/Kodiak Island to the eastern Bering Sea and back south to the Pacific. Thus, Kodiak can expect additional rounds of at least moderate intensity rain. All of this will lead to potential for flooding, which tends to happen on Kodiak with multiple days of intense rainfall. Rainfall totals through Sunday night look to be in the 3 to 6 inches range for the eastern side of Kodiak Island. Meanwhile, the aforementioned upper level ridge will build northwestward into Southcentral today, then strengthen over the Yukon and AK Interior Saturday. This will lead to a warming trend through Saturday, with interior Southcentral likely to see the hottest temperatures of the summer thus far. While confidence is high in significant subsidence from the ridge and rapidly warming low level temperatures, the one wildcard will be the extent of cloud cover on Saturday. The Gulf storm and strong upper level short- wave will track westward to Bristol Bay, but the tail end of the trough will lift northward toward Southcentral. This could bring a fairly extensive cloud shield inland, which will have some affect on high temperatures Saturday. In any case, rain will spread to the Gulf coast/eastern Kenai Peninsula by Saturday night. As the trough continues inland Saturday night, southeasterly gap winds will rapidly increase - likely leading to a mild and windy but dry night for much of the region. In the wake of the trough passage, Sunday looks to be a bit cooler than Saturday for Southcentral, but continued dry with gap winds likely persisting. -SEB && SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE ALEUTIANS (Days 1 through 3: Today through Sunday night)... Unsettled weather will persist through the weekend as a broad, upper-level low lingers near the Eastern Aleutians through Saturday. By Saturday afternoon, the low merges with an approaching low from the North Pacific and moves southeastwards towards the Gulf of Alaska. Upper shortwaves will continue rotating around the low through the weekend, driving weather across the region. Thus, the general expectation is for coastal Southwest to see cloudier and wetter conditions, whereas interior Southwest will have warmer and drier conditions. Gusty east to easterly winds will persist across much of Southwest through Sunday. For the Bering, expect northerly winds up to small craft. Here are the hazards/notable weather currently being monitored: * Periods of moderate to heavy rain (with storm totals hovering around 0.5 to 1 inch) likely on the Pacific side of the Alaska Peninsula as several waves of precipitation move in through the weekend. * Several rounds of gusty east-to-southeast winds, with gusts as high as 40-50 mph, for interior Bristol Bay through the weekend. * Daytime highs climb into the high 60s and low 70s this weekend for communities along Kuskokwim River. * Minimum RH values dropping into the low 30s and mid 20s for the Middle Kuskokwim Valley and Western Alaska Range this weekend. -AF/KC && .LONG TERM FORECAST (Days 4 through 7) Monday through Thursday... A couple of significant changes over the Alaska Weather Map through Thursday. A Rex block builds from the Arctic into Mainland Alaska through the period. This continues to support surface thermal troughs over the Eastern Interior. One closed low wobbles over the Gulf of Alaska and the Eastern North Pacific as it weakens. A low center entering the Western Bering slips along the Aleutians and merges with the Gulf low for Wednesday. With a ridge forming over the Kamchatka and Chukotsk Peninsula, a third center from the North Pacific with its front enters the pattern over the Central Aleutians on Thursday. A blend of Canadian/ECMWF/GFS and UKMET carries good confidence for the first half of the forecast, with the EC and GFS straying from the group by the end of the forecast. The Gulf low aloft links up with a well developed surface system for Monday and Tuesday. Locally heavy rainfall is expected across coastal Southcentral Alaska, with the highest amounts along the Eastern Kenai, Kodiak Island and parts of the Alaska Peninsula for the beginning of the week. Gusty winds less than gale force will occur along the North Gulf Coast, with gale force winds through the Barren Islands and Shelikof Strait for Monday, diminishing early Tuesday. Lesser amounts of rainfall moves inland to the Alaska Range, and along the West Coast down to Bristol Bay. The Aleutians and Bering will continue rain showers, with locally gusty winds across the Central Aleutians through Tuesday. Another area of gusty winds moves across the Pribilofs through Wednesday. Another area of locally heavy rainfall comes in over the Western and Central Aleutians with a low and its front late Wednesday into Thursday, spreading East through the week. -Kutz && .AVIATION... PANC...VFR conditions will persist. Turnagain Arm winds are expected to bend back over the terminal by around noon again tomorrow, then bend back away from the terminal by this evening. Wind gusts tomorrow afternoon will not be nearly as intense as they were yesterday, with peak gusts not expected to exceed 20 to 25 kts. && $$