TRUCKEE, Calif. — Keep the shovels handy: a powerful blizzard in the Sierra Nevada mountains was expected to wane Sunday, but more heavy snow is on the way.The National Weather Service said conditions would improve as winds weakened Sunday, but precipitation would quickly return, with heavy snow in some areas and rainfall in others. That wasn’t much of a break after a multiday storm that one meteorologist called “as bad as it gets” closed a key east-west freeway in northern…