Facebook lit up almost as brightly as the sky over Kotzebue and other areas of the Arctic last Sunday morning, as people speculated about what the bright flashes in the sky were.
More than a dozen people reported seeing several bright flashes in the sky, unexplained by air traffic or other human activity. One thought neighborhood children were pulling a prank at first. Another suggested a meteor had split into three parts. Another reported hearing booms.
Then came a post showing a Chicago-based meteorologist on The Weather Channel standing in a blinding snowstorm with the sky flashing behind him. The ecstatic reporter hooted as he and his camera man captured "thundersnow" on camera several times in the course of a few minutes.
Though rare, thundersnow is a real phenomenon, a snow thunderstorm that occurs under circumstances similar to a thunderstorm as a cold or warm front moves into an area. The thunder is often muffled by the snow, but the flashes may still be visible.
"It's pretty rare, but it's not out of the question in the winter," said John Lingaas, a meteorologist at the National Weather Service in Fairbanks. "The conditions have to be just right."
According to Lingaas, thundersnow occurs when warm, moist air is trapped below colder air at the upper levels. That produces cumulonimbus clouds and the two air masses turn over, producing lightning.
Lingaas said conditions in Kotzebue and surrounding areas did include some warmer air moving north that could have created enough instability to give rise to thundersnow.
"It doesn't happen every day, even in the Lower 48," he said. "It's pretty remarkable."
Lingaas said thundersnow is typically short-lived. It's not surprising that many theories existed about its source given the rareness of the event.
"I'm sure there was all kind of wondering," he said, adding that the weather service doesn't monitor meteor events, so he couldn't rule that out as a possible source of the early morning flashes.