Winds Caused by Difference in Pressure

Strong winds that roared across San Diego County on Tuesday resulted from an unusually strong air pressure difference between the desert and coast, according to Wilbur Shigehara, chief meteorologist for the National Weather Service at Lindbergh Field.

The greater the barometric pressure difference, the stronger the wind, Shigehara said, and the difference between San Diego and Palmdale, in the high desert northeast of Los Angeles, was significant: eight millibars compared to a usual five millibars during a Santa Ana condition.

A Santa Ana results from a high-pressure system building over the interior of the Western United States. Winds blow from high-pressure to low-pressure areas. The present high-pressure system centered near Boise, Idaho, has pushed wind patterns toward the Pacific. Southern California weather usually features a high-pressure cell offshore and results in light winds blowing inland from the ocean.

The National Weather Service at Lindbergh Field measured downtown winds Wednesday at 28 m.p.h., which Shigehara called very strong for the urban area. Winds were estimated at 75 m.p.h. in mountain passes of the Laguna Summit, along Interstate 8 east of San Diego.

Shigehara said Santa Ana winds tend to pick up speed as they cross mountain ranges because they are funneled through narrow canyons and passes. “It’s much like water being funneled through a narrow channel,” he said.

An aviation wind shear warning was issued for pilots landing at San Diego area airports after large differences in wind speeds were reported at different altitudes. Vertical wind shear can cause a plane to swerve unexpectedly.

Shigehara said the pressure difference should decrease gradually today and Thursday, resulting in less severe winds but maintaining the warm daytime temperatures. He said that warm, dry weather should prevail through the middle of next week and that the remainder of January should be warm with little rain.