The water level at Lake Oroville continued to drop Thursday as state officials pressed on with the effort to drain the reservoir in light of a forecast calling for an “atmospheric river” to strike the area beginning Monday. The lake level fell by nearly 5 feet in the 12-hour period ending at 8 a.m., dropping to below 869 feet. That was about 32 feet below the top of Oroville Dam even as the first in a series of storms hit the Oroville region late Wednesday.