A note from the county. You will likely start seeing more firefighting aircraft overhead. The Nevada County Airport and Grass Valley Air Attack Base are supporting training operations for CalFire air tankers and air attack aircraft for the next five to six weeks in preparation for fire season. According to a county memo, up to six firefighting aircraft per day will be training in the area for three days each week, depending upon the weather, so crews can hone their skills. The Air Attack Base usually opens for fire season June 15.