Extreme Santa Ana winds and low humidity are combining to create a dangerous wildfire threat early this week, according to the National Weather Service. Conditions are expected to be so bad that Southern California Edison is considering taking the unprecedented step of cutting power during peak winds to prevent fires sparked by downed power lines.
More than 13 million people are under a red-flag warning that covers parts of eight counties, including the greater Los Angeles area. The National Weather Service issues red-flag warnings when conditions are particularly dry and favorable for wildfires. It’s usually issued when humidity is forecast to drop below 25 percent. On Monday, humidity was expected to drop as low as 8 percent.
The driving force behind the low humidity is the Santa Ana winds, which in and of themselves will be a critical factor in this week’s fire conditions. High-wind warnings are in place for the high elevations surrounding Los Angeles. The National Weather Service expects widespread gusts of about 40 mph, but they could reach 75 mph “below passes and canyons and near the coastal slopes.”
The strongest winds were forecast to peak Monday morning, then weaken Monday afternoon. A second surge of wind was expected Tuesday morning, followed by weaker periods Wednesday and Thursday morning.
High-wind warnings mean that gusts could be strong enough for property damage to occur, but because these winds will be blowing from high elevation to low elevation, they also increase the wildfire risk exponentially.
Winds that flow from east to west sink along the elevation as it travels from mountains to sea level. As it does so, it is compressed, going from lower to higher pressure — we feel this when we drive out of the mountains and feel our ears pop. As air compresses, it heats up and the humidity naturally decreases because although the temperature is rising, the amount of moisture in the air stays the same.
The very strong, dry winds are creating the “potential for very rapid fire spread and extreme fire behavior which could threaten life and property,” the National Weather Service warned Monday.
“In the past, power equipment has been blamed for setting off wildfires that spread rapidly among the same type of dry, windy conditions expected overnight,” KABC-TV reports. Southern California Edison “is facing lawsuits over allegations its equipment was involved in starting the massive Thomas Fire” in 2017.
Every year, tens of thousands of acres and hundreds, sometimes thousands, of structures are burned to the ground in California wildfires. On average, the state’s fire season runs from spring to late fall. October happens to be one of the worst months historically because — unlike other parts of the country — the month tends to be extremely dry in California.
One of the reasons for this is the Santa Ana winds, which are more prevalent in fall and winter.
Wildfires took 54 lives in 2017 and cost U.S. taxpayers a record $18 billion, according to a National Oceanic and Atmospheric Administration report. Higher temperatures, drought and insect outbreaks, caused by or linked to climate change, have increased wildfires in the Southwest, according to the National Climate Assessment. “Numerous” models project more wildfires and increased risks to communities in coming decades.