The periodically heavy rain that spread across San Diego County on Tuesday afternoon will give way to a far more powerful and potentially damaging storm late Wednesday night, packing snow and rain that will last into late Thursday, with a third drenching possible late Sunday, the National Weather Service said. Collectively, the three storms could drop more than 1.5 inches of precipitation at the coast, twice as much inland, and 2 to 4 inches of snow above the 4,000-foot level, mostly on Thursday, when temperatures will be about 10 degrees below average throughout much of the region.