textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

An approaching Arctic trough across western Alaska is sinking towards Southcentral this morning. Light freezing drizzle overnight has switched over to very light snow for the Anchorage area for this morning. This very light precipitation could linger through the rest of this morning as the trough passes into Southcentral with weak upslope flow along the mountains. Snow for the Copper River Basin area will linger through the rest of this afternoon as the trough deepens in the northern Gulf tonight.

As precipitation ends, all attention will shift to a cold and windy pattern. The large scale pattern will continue to amplify through Friday, with a ridge in the Bering Sea and a trough over mainland AK and the Gulf. Colder Arctic air plunges south across Southcentral Friday (-20 to -25 degrees Celsius at 850mb). A surface low will form over the northeast Gulf and help tighten up pressure gradients. As the atmospheric flow becomes oriented N-S tonight, additional vorticity maxima embedded in the flow will drop southward across Southcentral into the Gulf, helping to strengthen winds at the surface. Even colder air will advect into interior Southcentral (as cold as -25 to -30 degrees Celsius at 850mb) Friday night into Saturday.

While most of the region will experience gusty northerly winds the next couple days, the strongest winds by far will be found along the coast and much of the Gulf coastal waters as winds accelerate offshore and through bays and passes. Beginning with the first surge of Arctic air from the northwest - Kodiak Island, the western Gulf, and Seward/Whittier areas will be favored for the strongest winds. This will gradually shift to Valdez/Thompson Pass and the Copper River Delta Friday. Multiple wind products have been issued to highlight the strong winds expected, with some potential to reach the high wind threshold (75 mph) in Kodiak City and Thompson Pass. There is some uncertainty in exactly how strong winds will get. Kodiak will be right along the western edge of the digging trough, so any shift will affect the winds. Meanwhile, for Valdez and Thompson Pass by the time the upper flow becomes really favorable for high winds, the bulk of the cold air advection has passed and the surface low in the Gulf is quickly exiting. Still, the thermal and pressure gradients between Valdez and the Copper Valley look impressive and passage of any vorticity maximum or short-wave trough could be just enough to produce high winds. Stay tuned as we continue to fine-tune the wind forecast.

Meanwhile, temperatures and wind chills will steadily fall over the next couple days. By Saturday morning, expect widespread temperatures below zero inland and in the single digits along the coast. Though winds will be diminishing most places by Saturday, wherever wind lingers wind chills will be well below zero. As is typical, the Copper River Basin can expect some of the coldest temperatures, with wind chills of -40 to -50 degrees possible by this weekend.

-SEB/Rux

AVIATION

PANC...MVFR conditions persist through the morning with a potential for periods of IFR conditions during light snowfall. VFR conditions will prevail when precipitation chances diminish in the late morning. Gusty northerly winds arrive in the afternoon once an upper trough dips into the region, lasting through Friday afternoon.