As more than half of the United States braces for a powerful winter storm, some meteorologists are warning on social media that “exploding trees” are possible.

Tree sap is mostly water with sugars and minerals, and like many liquids, it expands when it freezes. Gradual freezes usually don’t harm trees — even if it gradually cools to subzero — but plunging temperature swings cause uneven freezing and internal pressure. This stress can crack the bark and wood, producing what sounds like a loud pop.