Upper troughs and nasty weather to the North & South and the Bay Area keeps on blowing.

Bay Area dodges 2 wind killing bullets! But Southern California winds take one in the heart.

by Mike Godsey, mike@iwindsurf.comupper troughs2North&SouthAnim

Normally on a day like this I use the phrase “it’s a race with the clock” but I was tired of that hackneyed wording and too lazy to dream up a replacement. But it was a race and we won it! This video DOES NOT show the  North Pacific High’s NW surface winds. Rather we are looking a satellite view the clouds and moisture above 10,000 feet.

First look at the upper left corner of the video. You are seeing part of a huge upper trough at ≈ 18,000 ft. This southward extending loop has cold air to its north and warmer to its south. Where the two mix is a mass of moist clouds. At the surface far below this cloud mass is a rainy cold front and weak SW storm winds. As you can see this upper trough swings towards the Bay Area. You probably saw the very edge of these clouds to the NW today. This storm mass could have shoved the NPH south of the Bay Area and I would still be clearing egg from my face from one of the worse forecasts ever. But most models and the satellite imagery suggested that the system would not get close enough to shove the North Pacific High’s surface NW winds away from the Bay Area this afternoon. So the first wind killing bullet missed us as I forecast.

Now look at the video again west of Southern California. There is a broad upper trough in that area at ≈ 18,000 ft. and it has stirred up a counter-clockwise spinning low pressure below it which you can barely see. This system brought high clouds over Southern California’s inland valleys weakening the pressure gradient. Worse it jazzed up a wind killing Catalina Eddy that endured most of today.

But is also expanded towards the Bay Area and if all those clouds you see expanding from Southern California had reached the Bay Area only the coast would have blown as the SFO-SAC pressure gradient  plummeted. Once again my forecast hinged on that not happening in the Bay Area but I had no choice but to issue a low teen wind forecast for the Southern California sites.

See the 7PM forecast tonight to see  what happens to these wind killers overnight.

Posted in Los Angeles, San Diego, San Francisco