70 mph Santa Ana Winds

"Here come those Santa Ana Winds again"
-- Steely Dan

Santa Ana Winds are cranking up again over Southern California, threatening to rapidly spread any wildfires in the area. Fortunately, the NIFC says there are no major wildfires currently in Southern California.

Winds could exceed 70 mph in San Fernando. The National Weather Service has put up "Red Flag" (fire threat) Warnings, as well as various wind advisories. Look at our advisories map (PREMIUM | PRO) for detailed information.

What are Santa Ana Winds? Very simply, they are localized winds that develop in Southern California, blowing westward through the mountains. In the Fall, the Santa Ana Winds often aggravate wildfires by fanning their flames.

There are two websites that can educate you a lot on Santa Ana's if you're interested. One is UCLA's Santa Ana Page, the other is a page at UCSD. UCSD actually runs a "Santa Ana Index" which indicates when Santa Ana winds are likely. Ironically, just after I had finished explaining below why their warning "flag" (shown below) should change from green to red, it did.

If you look closely at what they monitor -- the list of weather conditions over time, you can see why we've just changed over from "code green" to "code red." Here's what I mean. Below I have highlighted in red numbers that trend towards Santa Ana winds. These weather conditions are read chronologically from top to bottom, so the most recent weather observations are at the bottom.

DltP means the Delta (difference) in Sea-Level Pressure (SLP) between SAN (column two, code for San Diego Airport) and ELY (column three, code for Ely, Nevada airport). Since a large difference in pressures creates high winds (meteorological principle), a rising DltP is bad and that's what we see most recently at the bottom of the list.

Next we look at the Temperature of the air (Tair) and the Dew Point Temperature (TDew). Here again, the highlighted recent Spread (Sprd), or difference between the two is bad because it indicates that the air is becoming more dry (and conversely, fog, frost or dew occurs when the air temperature equals its dew point).

Finally, the Wind Direction (Dir) needs to be between North-NorthWest (330 degrees on the compass) and East (90 degrees) for Santa Anas to form. Notice that in the last few sets of observations, the wind has come from that direction -- bad.