Deep snow can melt into a lot of water.
Deep snow very rarely causes flooding by itself. Often, heavy rain and rapid warm ups combine with rapidly melting snow to cause major flooding problems. For example, Fargo, S.D. had a 15 inch snow pack at the beginning of March 1994. Fortunately, slowly warming temperatures along with below freezing overnight temperatures through most of March into April reduced flooding from melting snow. Forecasters were originally concerned that the deep snow would pose significant problems during the spring thaw.