By Mike Godsey

by Mike Godsey,

This was not supposed to happen.

Today we were in a very clear eddy pattern with SW flow all day spoiling the 3rd Ave. winds.

And with a huge eddy slated for tomorrow, there was not a chance that this eddy would die.

And sure enough, by midmorning, anyone could see the eddy in the satellite imagery.

Check it out yourself in this first image.

See the spiral of fog and how it is shooting fog and southerly wind into Napa.

And of course, southerly flow means that the SW winds will pour through the Hwy. 92 Gap and wreck the launch site winds at 3rd Ave.

Now, look at the wind graph from our new 3rd Ave. beach sensor.

Yep, I was totally right about those SW 3rd Ave. launch winds.

That is, UNTIL 10 AM, when the wind abruptly turned from SW to WNW as you can see in the wind graph.

No biggie, I thought,  just a bit of weakening of eddies SW winds but they will come back.

But then those WNW winds began to build at 2 PM and reached into the low 20’s.

This utterly blew my forecast for unreliable launch winds.

My next thought was to figure out what happened so I could do a Backcast by Mike.

In this case, the proximal cause for the SW to WNW shift was easy. The eddy which had built like clockwork was demolished in the early afternoon by building WNW winds.

You can see this happening in this animation. Watch carefully as the eddy builds in the early morning.

But then it begins to drift towards Half Moon Bay.

Then the eddy is crushed against the coast. And all the friction of the Coast Range killed the eddies counterclockwise circulation.

Next, the WNW winds that had destroyed the eddy poured through the San Bruno Gap reaching the 3rd Ave. launch blowing my forecast to shreds.

There was no way I could have forecast this event… which is a pretty lame excuse. Have insights? Mail me at