Thundersnow is a problem for airplanes. In Finland, planes are actually more likely to be struck by lightning in the winter months because pilots know to avoid thunderclouds when it's warm out, but may not take the same precautions in colder weather, Mäkelä says. On one day in October 2011, ten different planes trying to depart from or land at Helsinki Airport were struck by lightning. When Mäkelä interviewed the pilots, some reported being temporarily blinded or deafened. The temperature on this day was a little above freezing, so the storm they were traveling through wasn't quite thundersnow, but it did demonstrate how much rarer cold-weather thunderstorms are—and how little pilots expect them to produce lightning.