Cut-Off Low Dies: After almost a week of SW flow just aloft the winds turn NW

by Mike Godsey, mike@iwindsurf.com

For many days the Bay Area has seen a combo of NW ocean surface winds and SW winds just aloft. NW surface winds typically curve and become more westerly as they come through the gaps in the Bay

Area coast range. This keeps the wind focus away from sties like Larkspur, Sherman in the AM, Pt. Isabel. But when the wind just aloft is SW we see a combo of NW and SWalmost every site in the Bay Area windy.

The SW flow aloft the last several days has been caused by a counter-clockwise spinning Cut-Off Low west of the Pacific Northwest which you can see in some of the blogs below. Today the Cut-Off Low has lunged eastward over the Columbia River Gorge. As the Cut-Off Low exits from the west coast an upper trough at ≈ 18,000 ft. moves over California. As this happens the winds aloft over the Bay clock from SW to W and then to NW.

You can see this happening if you study the last 1/3 of the video below and look at the model projections for powerful NW wind near near the surface this afternoon, in green.