Santa Ana Wildfire Threat Index could give SoCal residents advanced warning

A new predictive tool could give fire-wary Southern Californians advanced warning when conditions are ripe for devastating wildfires like the Cocos Fire, which burned dozens of homes in San Diego earlier this year.

The Santa Ana Wildfire Threat Index, announced Wednesday, will classify the fire threat potential of the notoriously hot, dry and strong "devil wind" so familiar to area residents.

It was developed by the U.S. Forest Service with help from UCLA and San Diego Gas & Electric, and the idea was sparked at least in part by the massive wildfires that swept across Southern California in 2007, according to U.S. Forest Service meteorologist Tom Rolinski.

That year, the Witch Fire alone destroyed 1,125 residential structures and left 40 firefighters injured and two people dead.

The new web-based tool will be used by fire agencies to help determine the severity of a wind event and make decisions about what resources are needed and where, and it will benefit the general public, as well, Rolinski told KPCC.

"I think most people in Southern California are not so concerned that it's going to be a windy day. What they're most concerned about is that, is there going to be a major wildfire today due to Santa Ana winds, and are they going to have to evacuate their home?" Rolinski said.

The index places Santa Ana wind events into one of five threat levels, ranging from no rating to extreme. Each level comes with corresponding actions authorities recommend residents take, according to Rolinski.

"Those recommended actions are things like gassing up your car, or charging your cell phone, make sure your escape routes are in place, make sure you have an evacuation plan. Those are all tied to the different threat levels, and that's going to help the general public be more prepared for  an upcoming event," Rolinski said.

The research behind the tool has been decades in the making, according to UCLA.

Most people living in the region are acquainted with how Santa Ana winds feel, but maybe not so much on the science behind them. The winds blow in from the northeast or east when the air is cooler in the desert, according to an online primer from UCLA professor Robert Fovell, who led the university's research team on the project.

"Forecasting winds is a tremendous challenge, and the reason for that is because that winds tend to vary so tremendously over relatively small scales, particularly in mountainous areas," Fovell told KPCC.

When high pressure builds over the Great Basin, a clockwise flow pushes air, which often starts as a cool or even cold wind, into the L.A. Basin. In many places, mountain passes and canyons act like wind tunnels, driving that air into fast-moving currents and creating the conditions in which a spark can ignite a firestorm.

But that's just the basics.

Three scientists, including Fovell, have been for decades performing high-resolution modeling for a large number of Santa Ana wind events, according to a statement from UCLA.

Fovell's team used several years of wind data to update an existing weather forecast model. They then compared the model to 30 years of historical weather reports and found it was quite accurate at predicting how winds are gonna blow around Southern California.

Fovell says his team combined the wind model with data on fire fuel and dryness in a given area to come up with the ratings for how dangerous possible fires might be. The research has led to improved understanding about how the winds form and evolve.

"We not only have a new, deeper understanding of how the San Diego-area terrain influences weather, especially wind, which is crucial to SDG&E’s operations, but we also have been able to make improvements in weather modeling that will benefit forecasters around the world," Fovell said in the statement.

The Forest Service tapped that knowledge to overhaul an internal tool that had already been in use for about five years, according to Rolinski.

The agencies worked together for about three years to get it ready for the public, and it spent a year in beta testing. During that time, Rolinski said, the index gave local authorities several days' advance notice on several prominent fires, including the Etiwanda Fire in Santa Barbara County and a series of San Diego fires in May of this year, as well as the Camarillo Springs Fire in 2013.

No predictive tool is perfect, of course. Rolinski made sure to note that the new service is not a guarantee that a major fire will break out.

But it could be a welcome tool for homeowners in the midst of a fierce fire season.

This story has been updated.