Fort Worth, Texas, shortly after the Oklahoma tornadoes. The distinctive, sac-like clouds are called mammatus clouds, and because they’re formed by wind shear, they are usually seen in conjunction with nasty weather. They’re a bit frightening, but undeniably beautiful.
I’ve only seen mammatus clouds in the Algarve on two occasions. The second time, they were lit up with an eerie yellowish color, and that was the day two tornadoes came ashore near Lagoa and Portimão.
(Click the image to wallpaperize.)