While driving through the Japanese city of Fujisawa last week, a Twitter user known as Poppy was shocked to look up and see what appeared to be a giant snowball floating in the sky.

"When I looked out of the car window, I saw a round ball-shaped cloud. I gazed at the cloud for a while then I rushed to take the photo," Poppy told local Japanese news outlet, Rocket News 24. "When I saw the cloud it was an even more spherical shape, so I regret not taking the photo more quickly."

https://twitter.com/pmxpvrtmx/status/805938180092411905

Poppy's sighting comes just over a year after another snowball cloud was captured in Japan by Twitter user Nico.

So, what exactly are these clouds and how do they form? Speculation is rife that they're everything from "roll clouds," created as airstreams flow over mountains, to a normal cloud that looks unusual due to the viewer's perspective. Another Twitter user says he photographed the same cloud above Fujisawa from another, decidedly-less spherical, angle.

Whatever the cause, there's no doubt that 2016 has seen its fair share of interesting cloud moments. From strange cloud formations over the Bermuda Triangle to increases in electric-blue night clouds above Antarctica, you never know what you'll see when you take a moment to look up.

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.