Up to 12 inches of rain below 8,500 feet is expected, and massive amounts of snow — up to 6 feet — above that elevation. A fourth, colder storm two days behind will drop yet more heavy snow. “It’s a once-in-10-year event,” said Zach Tolby, a meteorologist with the National Weather Service in Reno. “It’s the strongest storm we’ve seen in a long time, the kind of setup we look for to get significant flooding.”