Extremely High Fire Danger for Southern California as Santa Ana Winds Develop

Tom Moore
Published: September 25,2016
The first significant Santa Ana wind event of the season will keep residents of Southern California, who reside in areas vulnerable to fires, on edge into Monday.
The National Weather Service in Los Angeles issued a red flag warning for the mountains of Los Angeles and Ventura counties through 3 p.m. Monday for the valleys and coastal mountains of those two counties.
A combination of heat, low humidity levels and Santa Ana winds are responsible for the elevated fire threat.
(MORE: A Complete Rundown of All the Times Summer 2016's Weather Turned Weird and Violent)
Santa Ana winds are strong dry, downslope winds that often heat up and dry out Southern California. These winds can lead to fires.

Timeline For Santa Ana Wind Event

Red Flag Warnings

Into Monday
Conditions have become much more favorable for Santa Ana winds to increase and expand over a wider area. Sunday was very hot and dry across Southern California. High temperatures were well into the 80s in the mountains, while valley areas saw highs from the upper 90s to over 100 degrees.
Relative humidity levels have dipped into the single digits, so atmospheric conditions are extremely dry. Northeast winds will continue, and gusts in the valleys and coastal mountains could reach 40 mph into Monday. Gusts near 50 mph may occur in mountain areas.
The highest wind gusts should be in Los Angeles and Ventura counties. It is in these areas that the fire danger is highest; any fire that does ignite will likely spread very rapidly.
By later Monday afternoon, winds will begin to subside, but it will remain very hot and dry.

Forecast High Temperatures

(MORE: What Was Your Hottest Temperature This Summer ?)

Setup For Santa Ana Winds

Strong offshore winds (Santa Ana) develop across parts of Southern California.

Over the weekend, a high-pressure system built into the Great Basin, while a trough of low pressure established itself along the coastal area of Southern California.
The general wind flow is from higher pressure to lower pressure. The greater the difference in pressure (pressure gradient), the stronger the winds will be.
In this case, the winds will be blowing from the northeast, across Southern California and toward the ocean. These are known as Santa Ana winds.
The winds will come down the west side of the mountains that are situated to the east, along the border with Nevada. As a result, the air sinks and warms and becomes very dry, so relative humidity levels drop significantly.
MORE: California Fires-September 2016