More than 13 million under a flash flood advisory as Southern California gets first significant rain since May

Southern California is getting drenched for the first time in six months.

Rainfall started developing in southern parts of the state Tuesday night — the first substantial rain in Southern California since May.

More than 13 million people are under a flash flood advisory to include portions of California, southern Nevada and Utah, and most of Arizona, CNN Meteorologist Michael Guy said.

The storm is a combination of two weather systems — the remnants of a tropical depression from the East Pacific and a weather system from Canada, Guy said.

Farther east, parts of Arizona could pick up 2-4 inches of rain, and Phoenix could receive 1.5 inches.

In Southern California, rain started Tuesday night in parts of Orange County and Inland Empire. “Please take it easy on those roads as they are slick … turn around, don’t drown,” the National Weather Service tweeted.

Areas east and south of Los Angeles, including San Diego, could see up to an inch of rain, according to CNN Meteorologist Dave Hennen.

The rain will last until Friday, bringing relief to many drought-stricken areas. Much of California is still “abnormally dry,” according to the US drought monitor.

While the rain will help ease fire danger in Southern California, it won’t reach all the state’s most vulnerable areas. More than 3 million people in Northern California, including the Bay area, are under red flag warnings, meaning that weather conditions could result in wildfires. Winds there will be 35-45 mph, with gusts higher than 50 mph.

Dry conditions, low humidity and gusty winds will combine to create a heightened risk of wildfires during the next few days.

Later this week the storm system will move East, bringing rain and snow to the Rockies and the Midwest.