A flash flood watch is in effect as a once-a-decade rainstorm barrels toward Los Angeles

A powerful series of rainstorms is headed for California Thursday and through the weekend - arriving after a period of already severe weather in the state.

A flash flood watch is in effect throughout Los Angeles, Ventura, and souther Santa Barbara counties.

Over a foot of rain is expected in some places, as the storms drench a region from Northern California down to San Diego, raising safety concerns. Those concerns are perhaps most serious at the Oroville Dam, where unusually high waters damaged an emergency spillway February 9, forcing 188,000 residents to flee the area.

Efforts have been underway through the week to buttress the spillway, but a new rush of rainwater poses risks.

Los Angeles in particular will experience unusual weather, which is expected to begin Thursday night. Two to six inches are expected in the area, with up to an inch of rain falling per hour.

The forecast for Los Angeles has a 10-year return interval, according to Tom Dang, a National Weather Service meteorologist based out of Sacramento. That means that there's only a one-in-ten chance of seeing a storm this powerful in the area any given year, so that it would be expected about once a decade, or ten times in a century.

Torrential rain and wind also poses a risk of mudslides, wind damage, and road closures in parts of California, according to AccuWeather.

Flooding is possible across a swath of the state, with heavy snow expected high in the Sierra Nevadas.