Santa Ana Winds

In January 2025, wildfires devastated residential areas of southern California.

According to the California Department of Forestry and Fire Protection, as of 27 January, four distinct fires have killed 28 people, forced 200,000 to evacuate, and damaged 16,000 structures over 57,000 acres.

The scale and intensity of this disaster is difficult to fathom but some of the imagery from the area is harrowing.

Though the length of wildfire seasons has grown substantially in the past few decades, historically, the number of fires in January is low. What caused this brutal outbreak and why has it been so difficult to control?

Part of the fire math equation includes a drought, rather substantial in southern California since the summer of 2024, and a bout of low humidity. These ingredients make vegetation ripe for conflagration.

But what might be a localized terror can become a blitzkrieg from hell thanks to the Santa Ana winds. Fittingly, this phenomenon is sometimes called the devil winds.

Thanks to a combination of the Earth’s west-to-east spin, the Coriolis effect, and the latitudinal positioning of the continent, wind and weather patterns typically move roughly from west to east in North America. In California, this translates to wind and weather moving from the ocean to the mainland, which helps moderate the temperatures of coastal towns.

Santa Ana winds, as seen in the graphic above, toss these norms aside. As we’ve learned over the years studying anomalous weather and climate situations, extreme things tend to occur when a phenomenon can counteract the everyday mechanisms of the planet.

And the Santa Anas do not disappoint. These winds can bring hurricane-force gales to pacific California in the wrong direction, all without a storm! During the 2025 wildfires, windspeeds hit 100 miles per hour.

What causes these odd gales?

Recently, we learned about the Great Basin. This massive region, which includes most of Nevada and parts of Oregon, Idaho, California, and Utah, gets its name because the water flowing in its rivers does not go to the ocean. Instead, it either evaporates or disappears into the basin’s aquifers. Unsurprisingly, much of the Great Basin is desert.

This region also tends to attract high-pressure systems. In Part I of this series, we discovered that wind is the movement of air from areas of high pressure to those of low pressure. On large scales, in North America, winds move weather systems from west to east. However, we learned that other factors can influence winds on smaller scales. Katabatic winds – Greek for “descent” – combine the movement from high to low pressure with the power of gravity.

The Santa Ana winds are katabatic. If a high-pressure system sits over the Great Basin and a low-pressure system masses off the Pacific, winds will move from the inland desert toward the ocean. And, instead of a calm flow, gravity really gets going, as air moves from the heights of the Sierra Nevada, which includes the highest point in the contiguous United States, to the zero-point of the ocean. Amplifying the effect, the route from the mountains to the ocean is filled with canyons, which funnel the wind into veritable jets.

Air from the top of mountains is typically cool, so these winds bring refreshing breezes to the area, right? As we learned in Part II of the series, unfortunately, the opposite occurs. As the Santa Ana winds move from high elevations to low, not only do they gather speed, but they are also adiabatically heated. Because the pressure increases as elevation decreases, the air warms just because it receives more pressure. For every 1,000 feet in elevation loss, the air heats 5.4 degrees Fahrenheit.

Add it all together and the Santa Ana winds bring hot, dry air at high velocity to southern California.

Strong Santa Ana Winds in San Diego County

Most Santa Anas transpire in the autumn, though they can happen at any time of year. They are so warm that the hottest month in southern California isn’t July or August, as they are in most places in the northern hemisphere, but September.

If conditions are already parched – as they were in January 2025 – Santa Ana winds can spell doom for the region. The gusts do not bring humid air, which might mitigate fire risks; instead, they exacerbate the situation. Any spark in such a scenario could ignite a fire. But the really dangerous attribute comes from the speed. A fire that might burn a few trees somewhere can suddenly jump ridges, neighborhoods, or entire cities. The Santa Anas can transport embers from one area to another with scary quickness. This factor keeps firefighters from containing blazes and allows for the possibility of easy spreading.

January 2025’s wildfires were whipped around by winds that hit 100 miles per hour.

In a typical year, 10 to 25 Santa Ana episodes occur, usually spanning about three days. The longest ever was a 14-day marathon in 1957. Multiple blasts peppered California in January 2025, with just a few days of respite between the events, leaving firefighters with little time to make progress. Until they abate, we might have to make due with limiting damage.