rain

An unusual summer rain made for a wet walk in downtown Los Angeles on July 11. (Al Seib / Los Angeles Times / July 11, 2013)

The National Weather Service issued a flash flood watch Monday for portions of Los Angeles and Ventura counties.

A series of storm cells slowly making their way over Southern California’s mountains and the Antelope Valley could bring as much as half an inch of rain in 30 minutes to some areas, said meteorologist Rich Thompson.

The storm’s markedly slow pace increases the chances of flooding, he said. To boot, the moist air combined with the heat and storm cells could bring some thunder and lightning, too.

“There’s a lot of moisture in the atmosphere, it has a lot of water to work with,” Thompson said.

There is a slight chance of showers in downtown Los Angeles and along the coast.

“If people can survive today, they should be OK,” Thompson joked.

Temperatures across the Southland will teeter between the upper 70s and lower 80s, with cooler temperatures forecast for the mountains and beaches, Thompson said.

The wet weather should be limited to the deserts by Tuesday, he said.

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Joseph.serna@latimes.com

@josephserna