Look out weather watchers: La Niña is lurking. And that could mean a warm and dry winter for the USA’s southern tier and a potentially cooler, stormier one across the north, federal scientists announced Thursday morning. The La Niña climate pattern — marked by cooler-than-average ocean water in the central Pacific Ocean — is one of the main drivers of weather in the U.S. and around the world, especially during the late fall, winter and early spring.