A year ago 35.5% was covered to an average depth of 4.6 inches. The center watches snow cover and water content in part to predict how severe spring flooding may be when it melts.Winter storm warnings and weather advisories earlier this week stretched from New Mexico to Maine and affected 157 million people, the largest extent of such bulletins since 2005, according to the U.S. Weather Prediction Center.The cold and snow have crippled electric grids across the U.S. South, leaving thousands without power as utilities struggle to provide rising demand.