Snow in the Rockies, dry summers in the Southwest?

New simulations of summer rains in the arid American Southwest show that they are influenced by the previous winter's snowpack in the Rocky Mountains. Summer rains, called "monsoons," are the predominant source of rain in eastern Arizona and western New Mexico, says Michael Notaro , a climate scientist who is associate director at the Nelson Institute Center for Climatic Research at the University of Wisconsin-Madison. Anything that can help predict those rains could help protect people and an environment that are severely stressed by water shortages. Monsoons are summer rains that occur when moist air above an ocean, in this case the Pacific, flows over land and releases its water as rain. Monsoons are driven by a summertime temperature differential between hot air above the land and the cooler air over the ocean. Repeated studies have shown that the East Asian monsoon, which delivers heavy rain that supports intense agriculture in China and India, is influenced by snowpack in the Himalayas and Tibetan Plateau. Deep, extensive snowpack in the early spring translates into less rainfall in that summer, Notaro says, but nobody had tried to check for the same phenomenon in the North American monsoon.