Canada lynx (Lynx canadensis) and snowshoe hares (Lepus americanus) form a keystone predator-prey cycle that has large impacts on the North-American boreal forest vertebrate community. Snowshoe hares and lynx are both well-suited for snowy winters, but climate change associated shifts in snow conditions could lower hare survival and alter cyclic dynamics. Using detailed monitoring of snowshoe hare cause-specific mortality, behaviour, and prevailing weather, we demonstrate that hare mortality risk is strongly influenced by variation in snow conditions. Although predation risk from lynx was largely unaffected by snow conditions, coyote (Canis latrans) predation increased in shallow snow. Maximum snow depth in our study area has decreased 33% over the last two decades and predictions based on prolonged shallow snow indicate future hare survival could resemble that seen during population declines. Our results indicate that climate change could disrupt cyclic dynamics in the boreal forest.