Strange clouds were in the North Texas sky on Sunday night. Here's what they are.

Mammatus clouds spotted across North Texas

Many FOX 4 viewers sent in their photos and video of interesting cloud formations across North Texas on Sunday. FOX 4 meteorologist Evan Andrews talks a bit about mammatus clouds and how they are formed.

The FOX 4 newsroom received several pictures from viewers on Sunday of some interesting cloud formations.

The clouds with bulges or pouches are called Mammatus clouds.

They are called mammatus from the term mamma in Latin which means udder.

FOX 4 viewers from Frisco, McKinney, Heath and more sent in their photos of the odd looking clouds.

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Mammatus clouds in Heath (Courtesy: Derek Bush)

The large lumps on the undersides are formed by cold air sinking down to form pockets as opposed to the puffs of clouds rising through the convection of warm air.

Mammatus typically forms when there is turbulence within a cumulonimbus clouds.

The lack of stability that forms a Mammatus cloud usually means that there is also a chance of hail, heavy rain and lightning in the area.

The clouds were seen after strong storms moved through North Texas, leading to flooding and some hail.