NOAA's National Centers for Environmental Information
May, as expected, brought warm temperatures to North America, melting most of the remaining snow cover by the end of the month. The images above display the retreat of snow cover and oceanic ice across northern North America and the Northern Hemisphere. By the end of May, nearly all snow cover in the Rockies had melted, and most lakes in southern Canada were ice-free. Much of James Bay and the Hudson Bay retained their ice cover at the end of the month.
More information on May severe winter weather can also be found on NCDC's Hazards page.