Celebrate or lament the death of the August 17 to 22 Cut-Off Low?

by Mike Godsey, mike@iwindsurf.com

The formation of Cut-Off Lows are fascinating and you can see this one being created by scrolling down through recent blogs.
But today, August 17, we are seeing the death of the Cut-Off Low that hovered near the Bay Area at ≈ 18,000 ft. for over 5 days.
Why are are Cut-Off Lows so important in San Francisco Bay Area winds. And why are they loved by sailors and kiters in the Delta and the East Bay and so disliked by those on the coast, Crissy and Peninsula?

For the East Bay and Sherman Island a Cut-Off Low west of the Bay Area means an end of NW surface ocean wind so wind following the pressure gradient can more easily take a SW pathway through gaps in the coast range to the Central Valley. This brings the bulk of the wind to sites from Treasure Island eastward. A Cut-Off Low also means SW flow on the hilltops which helps the SW flow at the surface. And it also means a deeper marine layer which favors sites deeper inside the bay.

But a Cut-Off Low shrouds the coast  in deep marine layer clouds and the NW wind fades away at the surface since the North Pacific High’s surface NW winds are usually pushed far from the coast. It also mean SW flow at the surface which tends to push the wind away from the launches at Crissy, Coyote & 3rd. It also means late or scant clearing at the same sites which weakens the wind.

So while you watch this Cut-Off Lows lonely death up near the Oregon border you may feel sorrow or joy depending upon where your favorite waters are located.

And if you live in the Gorge you await the wind build up as the remains of the Cut-Off Low merge with an upper trough heading towards the Gorge.