Monday, March 4, 2024

Anchorage Wind

A reader inquired about the persistent north wind event of last week in the Anchorage area, so let's take a look at this.

First, the facts on the ground: there was indeed a very lengthy period of stiff northerly winds, lasting from early morning on Wednesday (Feb 28) through Saturday morning (March 2).  Here's a graphical look at observations from Anchorage airport, with wind speeds in mph:

Much the same sort of thing was observed up in Palmer, and with higher wind speeds, although there was a break on Thursday morning:

Remarkably, the peak wind gusts were 60mph or higher for 4 consecutive days in Palmer.  The maps below (click to enlarge) show the daily peak gusts from Feb 28 (top) to March 2 (bottom).  This was a remarkably persistent event:

Taking a quick look at historical hourly data from Anchorage airport, I see only one other event since 2000 with comparable sustained winds: it looks like a very similar event occurred at the same point on the calendar in 2017 (Feb 28 - March 3).  Here's the average MSLP for the 3 windiest days in both cases:  2017 (top) and 2024 (bottom):

Clearly the driving factor in both cases was the strong pressure gradient between low pressure in the eastern Gulf of Alaska and high pressure to the west and north.

The long duration of the event reflects the unusually persistent MSLP setup, with low pressure slow to depart or weaken in the Gulf of Alaska, and with building high pressure to the north maintaining the gradient as the low pressure eventually decayed.  Here's a sequence of MSLP analyses at 3am AKST for 5 consecutive days: February 27 through March 2.

Farther aloft, the situation was unusual, with a sharp ridge over the Bering Sea progressing slowly eastward behind a broad and deep trough over the Gulf of Alaska.  The 500mb map from Thursday afternoon shows powerful northwesterly flow in the very tight pressure gradient over southwestern Alaska, but yet the 500mb wind was out of the south at Anchorage (highlighted with the red circle below):

To me, this highlights the large degree of spin (technically "vorticity") in the atmosphere aloft, which helps explain the longevity of the low pressure in the northeastern Gulf of Alaska.  This upper trough and associated jet stream, by the way, is what brought extreme mountain snows to California over the weekend.  It was windy down there too: there's a lot of energy in this jet stream, and this is probably attributable to El Niño.

1 comment:

  1. That was me! Thanks for your insight and analysis!