Mammatus clouds form when sinking air is cooler than the surrounding air, according to EarthSky.org. Mammatus clouds. Ian Forsyth/Getty Images BBC describes mammatus clouds " pouch-like protrusions." ...

HOUSTON — Anvil clouds can often look like an alien spacecraft trying to land, We’ve had emails suggesting there is a UFO in the sky and immediately when I see the picture, it’s an anvil cloud.

ABC 13 Chief Meteorologist Travis Herzog said his inbox was flooded with photos of the "photogenic" cloud illuminated by the rising sun. "When a thunderstorm hits the top of the troposphere, the ...