On a recent mid-winter afternoon, sitting in the great room at Cain Vineyard & Winery on top of Spring Mountain, great slashes of wind-swept rain pounded the tall mullioned windows, finally washing down the panes as if one were trapped in an automobile inside a car wash. Fifteen minutes later, while the torrents persisted up on the mountain, down below as one descended into the village of St. Helena, the velocity of the rain had withered to a mere drizzle.