Congratulations, passengers aboard United Flight 5528 into Denver on Saturday night, you made it snow. More precisely, your airplane did, as did other aircraft landing at Denver International Airport that evening, but the United jet fared particularly well as a weather-maker, reports the Washington Post. In the story, meteorologist Matthew Cappucci explains that planes arriving between around 6pm and 7pm inadvertently flew through “a cloud of supercooled water droplets” and triggered a light snowfall. It was modest enough that nothing accumulated on the ground.

The phenomenon has been documented before, but it’s relatively rare and requires just the right combination of below-freezing temperatures and high relative humidity, explains a post at ViewFromtheWing. The “supercooled water droplets” mentioned above remain liquid under such conditions because they have “nothing to freeze onto to become snowflakes,” writes Cappucci. The jets give them that something—tiny particulates in the exhaust. The same general principle of “artificial ice nuclei” applies to the practice of cloud seeding, which CNN previously explained here. (More strange stuff stories.)