The National Weather Service has issued a red flag warning for Los Angeles and parts of Ventura County through Thursday evening, meaning wildfire conditions will be at their peak due to low humidity, ongoing drought and the arrival of strong Santa Ana winds

“DANGER!!! A life-threatening, destructive, widespread storm is expected across much of Ventura/LA Co. Tuesday afternoon into Wednesday morning. Areas that are not normally windy will be affected,” the National Weather Service in Los Angeles said in a statement posted on social media Monday.

Areas of “greatest concern” include the San Gabriel, Santa Susana and Santa Monica mountains and foothills, as well as the San Fernando Valley, Pasadena, Burbank, Hollywood, Beverly Hills, Simi Valley, Sylmar, Porter Ranch, Altadena and La Crescenta and Malibu, the National Weather Service said.

Wind gusts of between 50 and 80 mph are expected across the region, with gusts of up to 100 mph possible in some mountainous areas that have not seen significant rainfall in months.

“A red flag warning means that critical fire weather conditions are either occurring now or will occur shortly. Use extreme caution about anything that can start a wildfire,” the National Weather Service said. “Residents near wildland interfaces should be prepared to evacuate if a wildfire occurs.”

Storm warnings have also been posted in the mountains of Riverside and San Diego counties, where there is an increased risk of wildfires.

What are Santa Ana winds?

For Southern California residents, Santa Ana winds are nothing new.

“Santa Ana winds are dry and warm (often hot) winds in the Southern California region that blow from the desert – which includes the Great Basin of the western United States, including Nevada and parts of Utah,” says Robert Fovell, Professor of atmospheric and marine sciences at UCLA, says an FAQ posted on the university’s website.

The winds can blow any time the Great Basin gets cooler than Southern California. This most often happens between September and May.

“The Great Basin is higher than the LA Basin, which is near sea level. The air that flows into Southern California and forms the Santa Ana winds is weakening. As air sinks, it becomes compressed and its temperature rises,” Fovell explained.

Author Joan Didion introduced many Americans to the famous winds in her 1969 essay “The Santa Anas.”

“It’s hard for people who haven’t lived in Los Angeles to appreciate how radically Santa Ana figures in the local imagination. “The Burning City is Los Angeles’s deepest image of itself,” she wrote.

Drought continues to worsen in the south

The warnings come as much of the southern half of the state has experienced drier than normal weather. According to the U.S. Drought Monitor, affected areas are currently experiencing moderate drought conditions, and Ventura, Los Angeles, Orange, San Bernardino and Riverside counties are experiencing unusual drought or worse.

But that wasn’t the case for the entire state.

“Parts of San Diego County experienced the driest start to the season (and 9-month period overall) in over 150 years; The contrast between (anomalously wet) NorCal and (record dry) SoCal is even more anomalous than the northern wet or southern dry anomalies taken on their own,” wrote UCLA climate scientist Daniel Swain on his Weather West blog. “At the moment it is really a question of the ‘haves’ and ‘have-nots’ of rainfall – and there is no real prospect of this changing in the short term; Even in the long term, it remains possible that this general dipole will continue for the rest of the season (although hopefully with less extreme intensity).”

With dry conditions in the southern half of the state combined with strong Santa Ana winds, Southern California residents are prepared for the worst.

“Here we go again. Another wind event. … So the fire concerns will be the primary cause for us,” KTLA meteorologist Henry DiCarlo said Monday.