Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
898 FXAK68 PAFC 061252 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 452 AM AKDT Sun Oct 6 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Tuesday night)... A large upper level low circulation continues to be the dominant feature affecting Alaska. However, a new low which developed yesterday in the north-central Pacific has become the dominant low. It is tracking into the southwestern Gulf this morning, while the original low weakens as it drops south across the Alaska Peninsula and gets absorbed into the circulation of the newly developed low. An occluded front draped east-west across the southern Gulf will rotate north and west across the Gulf today, leading to increasing winds across the Gulf waters as well as Cook Inlet and Shelikof Strait. Based on observations overnight and the impressiveness of the low in satellite imagery, have generally upped the marine wind forecasts by 5 to 10 kts across the board. Meanwhile, a host of short-waves continue to rotate around the still very large cyclonic circulation aloft. One short-wave which brought showers to Anchorage and parts of the Mat-Su yesterday is now exiting across the Western Alaska Range to the Kuskokwim Valley. However, additional short-waves continue to stream in from the southeast, with widespread showers being observed across the northern Gulf and Prince William Sound regions. To the east of the low center, a jet streak is tracking northward across the central to eastern Gulf, driving short-waves northward toward eastern Prince William Sound and the Copper River Basin. The heaviest rain will be shunted eastward toward the northeast Gulf coast and Southeast Alaska. However, some rain will spread northward into the Copper River Basin tonight through Monday. Snow levels over Southcentral will gradually fall over the next couple days. Thompson Pas, which has seen some falling wet snow, will likely see some light accumulation on the roadway. Other passes surrounding the Copper River Basin could also see periods of wet snow, including Tahneta Pass/Eureka, Paxson to Isabel Pass, and Mentasta Pass. Model guidance displays a fairly large spread in the ultimate track of the low across the Gulf tonight through Monday night, leading to uncertainty in the wind and precipitation forecast. However, the general trend will be for the low to exit eastward with diminishing precipitation across Southcentral and Kodiak Island. The upper level pattern becomes quite messy by Tuesday, with the remnants of a trough, a short-wave ridge, and a new weakening trough approaching from the west. This will likely maintain significant cloudiness across the region (with some breaks), but little in the way of precipitation by Tuesday. Cold air advection will accompany the arrival of the short-wave trough in the western Gulf Monday night through Tuesday, leading to strengthening gap winds along the Alaska Peninsula and across Kodiak Island and the western Gulf. -SEB && .SHORT TERM FORECAST SOUTHWEST ALASKA, AND THE BERING SEA/ALEUTIANS... A large low, recently spanning the eastern Bering and coastal Southwest Alaska, departs to the south from Cold Bay this morning. In its wake, a swath of cold midlevel arctic air (minus 10 Celsius) will be drawn south across the Bering Sea. Northerly winds will increase again across the eastern Bering Sea from Nunivak Island and the Pribilofs south to the eastern Aleutians and the Shumagin Islands. Locations such as Cold Bay can expect northerly winds with gusts of 40 mph likely during the morning hours on Sunday and Monday. There is moderately low confidence on the exact peak magnitude of the wind gusts, however, cool, dense air could become enhanced through gaps, bays, and passes. Generally drier weather is expected for Southwest Alaska, as precipitation will likely be limited to prominent terrain. Meanwhile, over the western Bering, high pressure will continue to build through Monday morning before dipping south of the Aleutians ahead of two lows, one from Russia and one from Japan. Monday afternoon, the low out of Russia will swing through the northwestern Bering. Its front and associated precipitation will weaken Tuesday morning between Saint Matthew and Nunivak Island. Although there will be relatively warmer air advecting into the area, a few snowflakes cannot be ruled out for the Pribilofs and Saint Matthew Island. On Tuesday, the incoming system from Japan to the western Aleutians will be much warmer at the midlevel (0 to 4 Celsius). Although there is some model spread concerning the low`s center, the general track is expected to move west to east across the southern Bering Sea with its triple point hovering along the Aleutian Chain through midweek. Temperatures for the Aleutians are expected to be in the mid 40s to lower 50s. && .LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)... The global and regional models are in fair agreement through Friday with the persistent upper level trough over mainland Alaska and the Gulf becoming less defined into Friday as it begins to interact and merge with an upstream shortwave in the Bering Sea. The Canadian model suggests the upper level closed low remains over Central Alaska. However, preferred GFS/ECMWF solution that has the upper level low remaining over the South Central Alaska and the northern portion of the Gulf of Alaska. The surface low and attached fronts will quickly move over the Central Aleutians and Alaskan Peninsula Thursday and then stall out over Gulf of Alaska through Saturday. Scattered coastal precipitation and gale force northerly gap winds are likely as this impactful system crosses from the Bering Sea and into the Northern Gulf Friday and Saturday. High pressure will ridge into the Western Bering Sea ahead of another North Pacific system that approaches the area early next week. -DD && .AVIATION... PANC...VFR conditions and light winds will persist. Additional upper level short-waves moving in from the southeast today will likely bring showers back to the terminal. While exact timing is challenging, the best opportunity for showers will be between 18Z and 00Z today. Ceilings could briefly lower to around or just below 5000 feet in steadier showers. Ceilings will lift considerably tonight as upper flow backs around toward the north, bringing an end to the steady stream of short-waves from the Gulf. && $$