Warmer temperatures increase the elevation where falling snow melts and becomes rain, thus increasing the contributing area for a given storm and the likelihood of flooding (White et al. 2002; Lundquist et al. 2008). Mountain ranges lining the Pacific coast are most at risk from “atmospheric river” or “pineapple express” storms, when winds transfer a narrow jet of warm, moisture-rich air from near Hawaii to the U.S. West Coast (Ralph et al. 2004; Ralph et al. 2006; Neiman et al. 2008). This type of storm caused floods that closed Yosemite Valley in Yosemite National Park in January 1997 and May 2005, and floods that drastically damaged roads in Mount Rainier and North Cascades national parks in November 2006. Rivers with a large proportion of total contributing area near the mean elevation of the winter 0°C (32°F) isotherm are most sensitive to increased flood risks because these areas will become unfrozen and contribute to flood runoff as temperatures warm (Bales et al. 2006).