PG&E said in a news release that it made its decision based on a number factors, including the Red Flag Warnings issued by the National Weather Service this weekend, and reports from its crews in the affected areas.
While the warning is effective through 11 p.m. Monday, the extremely low humidity from the weekend and forecast downslope winds coming from the east made for particularly dangerous conditions Sunday night, said Craig Shoemaker, a meteorologist for the service at its Sacramento office.
“We’re expecting very strong winds tonight,” he said. “Normally at night, humidities increase and usually the temperatures drop, which tends to improve fire weather conditions, but the winds actually helped keep the temperatures warmer and the relative humidity higher. It kind of works together, especially with the downslope wind.”
Shoemaker said winds being pushed down the mountain to areas such as Placerville, Colfax and Jackson, as well as towns farther north along the foothills including Oroville and Nevada City, were expected to be between 15 and 30 mph through the night, with some localized gusts reaching 55 mph.