A Pacific storm supercharged by moisture from the subtropics slammed San Diego County on Thursday, flooding streets, snapping trees, closing schools, causing rock slides and delaying commercial airline traffic. The “atmospheric river” streamed ashore from east of Hawaii and dropped more than 10 inches of rain on Palomar Mountain, more than 6 inches in Julian and close to 3.5 inches in Oceanside. The system produced one of wettest winter days in decades, breaking daily rainfall records in seven communities, including Palomar. The mountain received 10.10 inches, snapping the record of 9.58 inches, set on Feb. 14, 1991. Ramona got 4.05 inches, nearly 2 inches higher than a record set in 1995.