A severe late spring storm in central Mexico in March 2016 that struck the Monarch Butterfly Biosphere Reserve was unique because it was accompanied by high-velocity winds that eliminated the normal thermal protection provided by the Oyamel fir forest. Temperatures throughout the forest merged with the colder open-area ambient temperatures. The storm was in effect a rain and snow storm sandwiched within a powerful and sustained wind storm, followed by lethal freezing that killed 31–38% of the butterflies in the Sierra Chincua and Cerro Pelón overwintering colonies.

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