What is the Elsinore Effect that’s seen on wildfires in the Lake Elsinore area?

The mixing of cooler air from the ocean and hot air from the valley causes winds to reverse course in the afternoon and abnormally burn downhill toward homes.

One of the accepted truths of wildfires is that flames burning on a mountain will naturally go uphill.

Firefighters know this, and it’s reflected in their tactics.

But in some cases, such as the Macy fire this week near Lake Elsinore, flames will burn downhill, too.

It’s not a coincidence that the phenomenon is called the Elsinore Effect, and Cal Fire/Riverside County Fire Department spokesman Rob Roseen said firefighters anticipated it Thursday when the fire broke out near the El Cariso Campground.

The name is often attributed to the Decker fire that in 1959 killed six firefighters who were burned in the Santa Ana Mountains near Lake Elsinore, although the wind-driven phenomenon can be seen in other places as well, such as in the Cajon Pass.

In Lake Elsinore, cooler air from the Pacific Ocean blows east from Orange County and mixes with the heated air from the valley in Riverside County in the afternoon, causing the uphill winds to reverse. That means flames, such as those in the Macy fire, reverse their path as well and begin marching toward homes. Firefighters staged their engines near homes in anticipation of that, Roseen said.

At nightfall, the winds reverse again and head uphill.

Daisy Rosales has lived at the base of the Santa Ana Mountains in Lake Elsinore for 26 years and appreciates the breezes from the ocean, up to a point.

“Because of that we get the coolest of the air and the lowest of the temperatures, more so than the city in front, which is good for us, but in a fire situation, it doesn’t help,” Rosales said Friday after the flames came so close to her home that she said she felt their heat.

One home did burn, the house at the top of Macy Street that was closest to the mountain. The flames could well have backed onto the property from the mountainside, a firefighter said.