Lack of rain in Southern California creates dangerous fire conditions

(December 6) Southern California is experiencing the worst fire season on record with a warm dry fall and very strong offshore winds. The situation may get worse as a dome of high-pressure air is forming above the West Coast that could keep the area dry for weeks.

A large fire called the Thomas Fire started in the foothills of Ventura County last Monday evening. The fire has devastated over 65,000 acres and caused 27,000 people to flee. New fires including one in the rich Bel-Air area of Los Angeles also recently broke out as described in a Digital Journal article.

Another recent article notes that the fires have led to the evacuation of nearly 200,000 people from threatened areas.

Hot dry winds are not abnormal in southern California but lack of rain is

The hot dry Santa Ana winds that blow as high as 70 miles per in southern California aren't that unusual for this time in early December according to Daniel Swain, a climate scientist at the University of California in Los Angeles. The winds start in the fall and continue throughout the winter.

What is unusual this year is a lack of rain. Swain says: "By this time of year, usually, there’s been some rain that’s wetted things down. It’s just as dry as it was in the summer months.”

The state of California gets most of its rain from October through to May, as strong winds in the upper atmosphere cause storms to roll in from the Pacific Ocean. By this time, Los Angeles an area where there are many fires usually should have had about two inches of rain. So far it has only about 5 percent of that, just a tenth of an inch.

In Northern California there have been many rain showers. National Weather Service meteorologist David Sweet describes the Burbank area as quite parched.

The atmospheric ridge in Southern California

The storms carried in by the jet stream from the Pacific can be diverted if there are high-pressure bubbles of warm air. These are called an atmospheric ridge. This is what is causing the present dry spell in southern California.

Swain notes that an even larger ridge is forming along the entire West Coast of the US. Rainfall could be shunted into Canada or even Alaska. Swain claims: “We were dry before and now the prospects for rain look even less likely because of the size of this thing.”

Atmospheric ridges a recurring problem

An atmospheric ridge has been over California for three winters in a row, creating a record-setting drought lasting five years now.

Swain said the real question was how long the ridge remained over the area. During the drought the ridges had lasted for months at a time. Swain says the ridges are becoming more common with global warming according to a study he and others did in 2016.

As the polar ice melts, there is a chain reaction that in the end helps these atmospheric ridges form and ultimately keep rain from falling over Southern California according to recent research led by Ivana Cvijanovic of the Lawrence National Laboratory.

However, Civijanovic cautions readers that the study is not a prediction as many other factors can influence what happens in the future. Another recent study suggests that California could become wetter.

For now the weather predictions for more windy weather means firefighters have a long battle ahead of them. What is needed is for enough rain to douse the flames and turn things green again.

Previously published in Digital Journal