SAN DIEGO (FOX 5/KUSI) -- The Mountain Empire Unified School District announced school closures for the second day in a row. On Wednesday, the school district did not have classes due to high winds. A power shutoff affecting multiple school sites has forced Mountain Empire Unified to cancel classes for Thursday, according to the San Diego County Office of Education. "The safety of students and school staff is of the utmost importance to San Diego County school districts," the educational institution said. Critical fire weather in San Diego County as Red Flag Warnings take effect The power shutoff comes amid a Red Flag Warning in effect through Thursday evening for San Diego County valleys due to dangerously low relative humidity and gusty northeast to easterly winds. The warning will remain in place for mountain areas through Friday. San Diego Gas & Electric has begun rolling power shutoffs for thousands of customers in the county’s backcountry to reduce the risk of wildfires. For real-time updates, follow @SanDiegoCOE on X, formerly known as Twitter.