Before the big thunderstorm arrived last Tuesday night, I sat outside and sketched some strange cloud formations.
They're called mammatus clouds, named so because their pendulous forms resemble an animal's udder or a woman's breasts. They are found at the base of anvil clouds, the giant cumulonimbus clouds that generate extreme thunderstorms.
As I made this quick notation with my water brushes, the wind whipped the treetops. The clouds swirled and turned green. Big raindrops started falling around me. I folded up my sketch gear and retreated indoors. Hail pounded the deck outside. Lightning flashed, then thunder. Suddenly the electric power died and stayed out for several hours.
I finished the sketch by the light of a kerosene lantern.
Mammatus clouds on Wikipedia