textproduct: Anchorage

LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)

The overall upper-level pattern through Wednesday will be dominated by a ridge of high pressure extending from the North Pacific across the Aleutian Islands and southern Bering Sea with a negatively tilted trough with axis extending from the Chukchi Sea southeast to the eastern Gulf of Alaska.

Multiple shortwaves and vorticity maxima will move from northwest Alaska into the Gulf, embedded in the northwesterly flow aloft. For Tuesday, the first of these features will help maintain gusty gap winds from Alaska Peninsula east across the immediate Southcentral coast to Prince William Sound. A transient ridge in the wake of this wave will provide some warm air advection, allowing snow level to rise from an expected minimum around 3,000 ft on Monday. A second, weaker wave moves through on Wednesday, allowing for a return of scattered showers across the Alaska Range and the higher terrain surrounding the Copper River Basin.

By late Wednesday, the upper-level pattern looks to become more amplified, with the North Pacific Ridge moving east and lifting across the Southern Mainland Thursday morning. The eastward progression of this ridge will allow a trough over the western Bering to deepen, resulting in a stout southerly wind flow between the two features. A strong shortwave will move north along a stalled frontal boundary, leading to the development of a surface low somewhere between the Pribilofs and Kuskokwim Delta coast. This feature, along with its surface front, will drive into Southwest Alaska with another round of heavy rain and gusty southwesterly winds along the coast for Thursday.

By late Thursday, model agreement begins to break down more significantly, particularly with regard to the eastward progression of the upper-level ridge. The GFS and Canadian models are favored for the long term forecast, both of which slide the ridge axis over the Alaska Panhandle by Friday. The resultant flow aloft becomes more southwesterly across the Alaska Peninsula and Southern Mainland as the trough also slides east. Multiple shortwave then looks to lift from the North Pacific to the Alaska Peninsula by the end of the week, with more rain and gusty winds for much of Southwest and western half of Southcentral Alaska as yet another storm system drives north across western Alaska.

- TM

AVIATION

PANC...Ceilings and visibility will fluctuate between VRF and MVFR through tonight, although VFR is expected to prevail with ceilings around 4,000 ft. Any drop to MVFR will likely be in rain showers that may pass over the terminal late this afternoon through evening. Strong southeasterly winds and gusts will continue through around midnight before quickly diminishing overnight. The strongest of these winds, with gusts around 50 mph, are expected to persist through around 7 pm this evening.

The biggest challenge will be the extent of clearing overnight and into early Saturday morning in the wake of this system. The flow aloft and near the surface will quickly weaken, becoming light and variable early Saturday morning, before a drier and more northerly flow develops after sunrise. Given the weaker flow developing overnight, the forecast leans toward ceilings lowering back to MVFR (as low as 1,500 ft) by 12z and lingering through 18z before lifting and eroding late Saturday morning as a light northerly wind develops.