Heat wave ends and marine surge fizzles as Upper level high pressure retreats too fast.

by Mike Godsey, mike@iwindsurf.com

Well last Thursday I forecast a major marine surge to hit the S. F. Bay yesterday and there is no hint to masses of cool fog and upperHPretreatsNOsurgeAnim strong SW wind pouring through the Golden Gate. What happened? The simple answer is that yesterday the marine surge climbed up the coast from Southern California waters and even made it to the entrance of the Golden Gate but the NW wind out at the ocean buoys was just to strong for the marine surge to reach its potential. But there is more to it than that. Since the NW winds are usually absent at the coast in the early AM it is common for the southerly marine surge to sneak up the coast and blast into the bay despite NW winds over the outer waters. Basically during a normal marine surge the key to getting that fog into the bay is the retreat of the heat wave. When this happens at the normal pace the high pressure leaves a lobe of hot low pressure air over the ocean just north of the Golden Gate. This really causes the marine surge to shoot up the coast to the Hwy. 92 gap and the Golden Gate where it encounters the strong pressure gradient to the Central Valley and rushes into the bay.

But as you can see in the satellite video the upper level high pressure, note clockwise winds and clouds, retreated so fast that there was only a brief low pressure north of the Golden Gate yesterday morning. And then when the NW winds made their normal afternoon push towards the coast they wiped out what remained of the marine surge.