Powerful Santa Ana winds are sweeping across Southern California in a windstorm that triggered red flag warnings for Los Angeles County and created what firefighters called some of the most dangerous conditions the fire-prone region has ever seen.
Wind speeds increased Tuesday morning, not long before a wildfire broke out in Pacific Palisades, with the strongest gusts Tuesday evening into Wednesday. Gusts up to 60 to 70 mph are possible with mountaintop winds reaching 100 mph.
So why is it so windy?
Get top local stories in Southern California delivered to you every morning. >Sign up for NBC LA's News Headlines newsletter.
What to know about Santa Ana winds
Wind moves from high pressure to low pressure. When you add Southern California's rugged topography of mountains, canyons and passes, that wind can now pick up speed as it's channeled through those areas.
"They're specific to our area because of the topography," said NBC4 meteorologist Shanna Mendiola. "High pressure and low pressure play a big part in this. Our winds flow from high to low, and they come through the passes and canyons. We call these the offshore winds. They come from the deserts through the passes over the mountains and compress downhill."
As the air gets to the top of the mountain it races down, it acts like a bike with no brakes and gaining speed. The canyons and passes act as a toll road. The wind piles up and once it squeezes through the canyon it races out in a powerful blast of wind.
And wind that is moving down a mountain dries as it sinks. It’s more physics than meteorology, but this drying lowers the humidity into the single digits. The combination of dry fuels, low humidity, and strong gusty winds create a critical fire weather threat. If a fire starts it can spread rapidly and behave erratically due to wind gusts.
Santa Ana winds occur in the fall lasting through the winter.
Send us your windstorm photos
