Flash Floods Possible for San Diego, Los Angeles as Thunderstorms Approach Following Two Months of Drought

As thunderstorms start to move into the area after about two months of extreme drought, flash floods are a possibility for cities like San Diego and Los Angeles.

Due to the increase in moisture associated with the North American monsoon, coastal regions from the Mexico border all the way up to the mountains north of Los Angeles might experience their first shower or thunderstorm In May or June.

Rarely does it rain along the Southern California coast in the summer and early fall, but the current weather pattern may bring some rain to the region by next week. Although the anticipated widely separated thunderstorm activity is not expected to significantly affect the long-term drought, some roads may become slippery as flash flooding may affect some communities well inland, according to forecasters.

On the first full day of astronomical summer, June 22, just 0.01 of an inch of rain fell in Downtown Los Angeles. Only a few raindrops have fallen along parts of the Southern California coast since the spring. The most recent general soaker brought 0.10-0.50 inches of rain to the Los Angeles area on April 21-22.

San Diego, further south along the California Coast, only received 0.02 of an inch of rain on May 20-barely enough to moisten the ground. On March 28-29, when roughly 0.70 of an inch was measured in the city's rain gauges, the San Diego region last experienced significant rainfall.

The Weather Streak Disturbance

In response to this disturbance, there will be an increase in moisture, which will appear as high and mid-level cloud cover rather than the low clouds that the Pacific Ocean is famous for. On Wednesday, a disturbance visible on satellite images was changing direction toward the northwest from Arizona and Mexico. On Thursday, the day that these clouds move across Southern California, they will rotate over that region. There may be sufficient additional moisture in the atmosphere on Thursday to cause shower and thunderstorm activity over parts of interior Southern California.

With a few exceptions, the slightly drier air that will follow this feature's departure may once again restrict the activity of thunderstorms over the area on Friday and Saturday.

Localized Rainshowers

Through next Tuesday, as the monsoon's moisture surges and wanes a few times, pockets of 0.25 to 0.50 of an inch of rain with sporadic amounts of 1-2 inches are possible over interior Southern California.

Even in the heaviest downpours, there won't be enough rain to produce widespread runoff and significantly affect Southern California's drought conditions. As early as next week, the California cities of Palm Springs and Victorville are among those that could experience numerous occasions of thunderstorm downpours as early as next week. Since June 22, when 0.03 of an inch of measurable rain fell, there has been no measurable rain in the area around Palm Springs, despite a few thunderstorms so far this summer.

In addition to the potential for downpours that could briefly soak communities in the desert and mountains, there is also a chance of intensely localized flash flooding. Thunderstorms associated with the 2022 North American monsoon season have recently caused flash flooding in the metro areas of Phoenix, Flagstaff, as well as Tucson in Arizona as well as Las Vegas.

The risk of flash flooding as well as the mudslides that go along with it will be greatest in areas of Southern California close to recent burn scars.

Probable Flash Floods

On Monday, when there is the greatest likelihood of a thunderstorm, the threat of flash floods is very low in Los Angeles and San Diego. Where it does manage to rain, however, the moisture and oil buildup from cars during the summer and late spring can make road surfaces especially slick. There hasn't been much rain to wash the greasy substances away.

There will be a risk of thunderstorms producing very little to no rainfall in addition to the increase in rainstorms over interior Southern California. The storms' associated lightning and strong winds may start fresh wildfires.

Lightning is still a potential ignition source for the state's deadliest active fire, the McKinney Fire, whose cause is still under investigation. The fire is thought to have started in the afternoon of July 29 when storms were in the area of Southern Oregon, and Northern California, according to AccuWeather Meteorologist Ryan Adamson. National Incident Information System and Cal Fire data say that, as of Wednesday, the fire in California's northern tier had scorched 57,500 acres and was only about 0% contained.