Santa Ana winds can down trees, trigger power outages and even damage buildings. They're also notorious for fanning some of the most destructive wildfires in Southern California history.

What are Santa Ana winds?

These winds form when an area of high pressure builds over the Great Basin, a region in the Intermountain West that includes Nevada and parts of other neighboring states.

When this high forms, it creates a sharp pressure difference between the interior and the coast. Air then rushes downhill to the sea in an attempt to create balance.

But there's an issue: California's mountain ranges get in the way.

(MORE: The Pineapple Express is a firehose, and El Niño just turned it up)

This air is forced to squeeze through narrower mountain passes and canyons. One of these mountain ranges is the Santa Ana Mountains in Orange County, which is how these winds got their name in the first place.

Get More of Our News on Google

Set The Weather Company as a 'Preferred Source' to get quicker access to the news you value.

When the wind is squeezed into these narrow paths, it speeds up dramatically. Gusts often reach 70 mph, but in the most intense events, they can top 100 mph.

These winds worsen when you have upper-level low pressure swirling in or near Arizona. That enhances the pressure gradient and can further increase the wind speeds, making them more widespread in Southern California rather than only below passes and canyons.

(MORE: Is hurricane season over? Here's what past super El Niños have shown)

They are hot and dry, too

It's not just that these winds are fast — they're also hot and dry, and there are a few reasons why.

1. Origination: These winds begin in the Great Basin, a very dry and arid landscape. That means these winds don't have much moisture to begin with.
2. Heating up descending mountains: When air travels down the mountain, it undergoes a process called adiabatic warming. This occurs because air that descends in the atmosphere compresses due to higher air pressure and therefore heats up.
3. Air squeezes between mountains: When air is squeezed into narrow passageways, it speeds up as it descends. This enhances the rapid warming due to descending in the atmosphere.

When are these winds worse?

The season runs primarily from October through March, though events can occur as early as September or as late as June. Winds tend to peak overnight and into the early morning, when desert cooling strengthens the pressure difference driving them.

What makes Santa Ana winds especially hazardous isn't just their speed — it's the timing. They typically arrive in fall, right when Southern California's vegetation is at its driest after a long, rainless summer.

(MORE: Use these two numbers to avoid cleaning your gutters twice)

The impacts of these winds

These winds are most known for their wildfire risk.

A small spark, whether from a downed power line, a vehicle or a campfire, can explode into a major wildfire within minutes under these conditions.

Some of the state's most destructive fires on record have broken out during Santa Ana events. And should the wildfire season be particularly deadly, you'll see more landslides across these burn scars when the rainy season comes.

The Camp Fire, which destroyed nearly 19,000 structures in Butte County in November 2018, ranks as California's most destructive wildfire, according to Cal Fire. However, a majority of California's most destructive wildfires have occurred in October.

Of course, these high winds can also down trees, knock out power, damage mobile homes, blow cars and trucks off the road and produce areas of blowing dust and reduced visibility.

They also can produce dangerous low-level wind shear and turbulence for planes, as many approaches and climbs after takeoff occur over the mountains. They can even be a boating hazard.

Santa Ana winds can howl far offshore, reaching all the way to the Channel, Catalina and San Clemente islands.

Heavy surf can develop over the waters immediately adjacent to the mouth of canyons, as well as northeast-facing harbors of the aforementioned islands.