Absolutely Sick Mammas 1

Last evening was something! I was working and then I just went out and saw this "apocalyptical" sky over my head (Montreal). Severe thunderstorms were observed during the evening around Montreal and the cell was as same as in the books : perfect, well structured. I think I spent 45 minutes hanging out outside and taking picture, though it was risky since the thunderstorm was reported to produce hailstorms as well (finally we just received melted hail as highly dense precipitations).

Those clouds are called mammatus and are usually observed under the highly stable parts of a thunderstorm cloud (cumulonimbus) -- the anvil. They are produced when they are downdrafts under the stable part of the anvil. The best time to observe them are at sunset, when a thunderstorm's passing.