Between August 14 and August 16, Northern California was subjected to record-breaking warm temperatures,[8][9][10] due to anomalously strong high pressure over the region. Early on August 15, the National Weather Service for San Francisco issued a Fire Weather Watch[11] highlighting the risk of wildfire starts due to the combination of lightning risk due to moist, unstable air aloft, dry fuels, and hot temperatures near the surface. Later that day, the Fire Weather Watch was upgraded to a Red Flag Warning,[12] noting the risk of abundant lighting already apparent as the storms moved toward the region from the south.