Story highlights Storm approaches Northern California and is expected to bring rain throughout weekend

Sheriff warns residents to remain vigilant despite lifting mandatory evacuation order

Oroville, California (CNN) Rain is expected Thursday in the Northern California area around Lake Oroville, as crews work to reduce the water level there.

Earlier this week, authorities ordered mandatory evacuations over concerns that an emergency spillway at the Oroville Dam could fail and threaten nearby communities. On Tuesday, officials downgraded the evacuation order to a warning, allowing 188,000 evacuees from Butte, Sutter and Yuba counties to return home.

In a news conference Wednesday, Butte County Sheriff Kory Honea emphasized that even though the mandatory evacuation has been lifted, this remains an emergency situation.

"The risk level was reduced that I felt people could return to the area, however they need to maintain vigilance," Honea said.

A series of storms are heading into the region, but they are smaller than previous ones. These storms are expected to persist through the weekend. A flash flood watch is in effect until Sunday.

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