Oct 22 2008
Anatomy of a Santa Ana Wind Storm
Fall in Southern California means Santa Ana winds. Its the changing of the seasons, when pressure gradients form between a High and a Low. This causes the winds to blow from the hot deserts to the coast, creating an offshore wind event. What you hear most about in these blue sky storms are the fires. These occur, because the tiniest of sparks, either man made or by accident, are picked up immediately by the raging winds, which can create a firestorm.
This is the 11am graphical forecast on 11/22 on Sailflow. Of special interest is the comparison of this graphic to the graphic of Hurricane Omar in my last post. That pretty pink color reflects a forecast of winds in excess of 40+ knots. While a hurricane is certainly forboding to those in its path, Santa Ana’s are much more sublime. All of a sudden it is hot on the coast, its beautifully clear and bright blue skies but the wind is of gale strength and has been known to reach Cat1 periodically…
For mariners, this obviously creates hazards. Normal harbors and anchorages out at the Channel Islands become lee shores; perhaps the most feared of situations for sailors. Not to mention opposite swell sets and more fun stuff like that… Surfers on the other hand like it a lot !
This is our 2nd Santa Ana of this Fall season and probably not the last.
Your reference of the winds blowing from the Great Basin under (Santa Anas) causes an off shore wind is not quite correct. The off shore winds are caused by the high pressure that forms over the Great Basin, due to cold air in the fall which turns in a clock wise direction. This movement of air is forced down the canyons, which you have mentioned, but it is the conpressional heating, that causes the high temps to form. This is much like poking holes into a full can of water. There isn’t much water movement in the can, but the water flowing out of the can is quite dramatic.