LOS ANGELES (CBSLA.com) — The usual May gray might bring some rain to Southern California and a chance of thunderstorms, especially in the San Gabriel Mountains and the Antelope Valley.

With upper-level winds expected to be weak, the storm is likely to be slow-moving, generating rainfall rates exceeding an inch per hour and creating a risk of flash-flooding, according to a National Weather Service statement.

A flash flood watch will be in effect in the San Gabriel Mountains in Los Angeles and Ventura counties and the Antelope Valley from noon until 8 p.m.

“Any storm that forms may produce dangerous lightning, gusty winds, heavy showers, and hail,” the weather service warned in a statement.

“Heavier showers may result in localized flooding of roadways, small creeks, and old burn areas. Outdoor activities such as hiking and boating will be especially affected.”

In addition to flash-flooding, the storm could unleash slides of rocks and mud and spark mud and debris flows over slopes denuded by wildfires, the statement said.

While the greatest risk of thunderstorms was in the San Gabriel Mountains and Antelope Valley, “a few could drift into the adjacent valleys and even coastal areas,” and “there will be a slight chance for thunderstorms just about anywhere” today, according to the NWS.

The prospect of thunderstorms also threatened mariners, with forecasters warning of isolated thunderstorms over coastal waters.

“Any thunderstorms that form will be capable of producing locally gusty winds and rough seas, dangerous lightning, small hail and heavy rainfall, with reduced visibility,” a statement said.

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