The Cleveland NWS office captures this ominous photo of an arcus, or shelf cloud, over the city this week. PHOTO COURTESY NWS, Cleveland

So what’s an “arcus cloud?”

They can look like something out of a movie, an alien invasion on the horizon, but the bizarre shape in the sky is an arcus cloud.

>>Live Doppler 7 Radar

Arcus cloud is the umbrella term for a low, horizontal cloud formation that usually accompany’s thunderstorms. You may know them as shelf clouds and roll clouds.

This is an arcus cloud, or shelf cloud, seen over Celina, Ohio this week, May 2018. CONTRIBUTED PHOTO

>>RELATED: What’s the difference between a shelf cloud and a wall cloud?

We see both types of these arcus clouds in the Miami Valley. In northeast Ohio this week, a complex of thunderstorms produced some impressive shelf cloud photos.

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