Strange clouds over London spark mystery during Trump visit

Caroline FloydMeteorologist

Aliens? Apocalypse? Asperitas.

While it wasn't the mothership descending on London during Trump's visit earlier this week, it definitely looked like it to some residents.

Creepy-looking skies were snapped across the city's south end on Tuesday as a massive vortex-like cloud hovered overhead, prompting Londoners to ask "What is that thing?" on social media.

Summer revealed! Visit our Complete Guide to Summer 2019 for an in-depth look at the Summer Forecast, tips to plan for it and much more

So if it wasn't aliens or the apocalypse, what was it?

Judging by the images, the clouds look to be what are known as asperitas, a relatively new classification given to the undulating, ominous-looking formation in 2017.

"Asperitas is a distinctive, but relatively rare cloud formation that takes the appearance of rippling waves," the U.K. Met Office told ITV News. "These wave-like structures form on the underside of the cloud to make it look like a rough sea surface when viewed from below."

MUST SEE: TIME-LAPSE VIDEO OF ASPERITAS CLOUDS IN NEBRASKA

While some theorize that the wave-like clouds are associated with the aftermath of thunderstorms, there are reports they've been spotted in calm weather, too, making them all the more mysterious.

WATCH BELOW: CLOUDS 101 - HOW DO CLOUDS WORK?