Cut-Off Low unexpectedly kills Southern California coast winds.

by Mike Godsey,

The forecast was clear that the winds were in jeopardy today due to a nagging vague Catalina Eddy Cut-Off LowCloudsKillscAnimand the threat of clouds forming due to a Cut-Off Low over the S. F. Bay Area. But nothing in the forecast prepared you for the almost complete lack of wind.

So what happened?

Well for one the vague Catalina Eddy did not die until after 1 PM. but that would only drop Cabrillo and Leo winds into the mid teens.

So what almost completely wiped out the wind? Remember that Cut-Off Low over the Bay Area and my 7AM warning that clouds from it could wreck the heating of the inland valleys and the pressure gradient? Well there was no hint of those clouds at the 11:30 AM update so I dropped the warning. But what I could  not see was the mass of invisible water vapor from the Cut-Off Low that was heading towards the Southern California mountains. As you can see in the satellite video when this mass of moist air climbed up the mountain slopes it cooled and vapor condensed into clouds and stopped the inland valley heating. So we never got the expected heating and pressure gradient.

So what I learned is that when there is a Cut-Off Low north of Southern California I can not just look for visible clouds but I have to look at the water vapor satellite imagery and allow for FAST cloud formation.