We had another couple weeks of severe storms here. On Sunday, after a couple hours in the basement under a tornado warning, we emerged to see this in the skies toward the southwest:
They are "Mammatus" clouds. We just call them "bubble clouds".
Mammatus, also known as mammatocumulus (meaning "mammary cloud" or "breast cloud"), is a meteorological term applied to a cellular pattern of pouches hanging underneath the base of a cloud. The name mammatus is derived from the Latin mamma (meaning "udder" or "breast").
Mammatus are most often associated with the anvil cloud and also severe thunderstorms...In the United States, sky gazers may be most familiar with the very distinct and more common cumulonimbus mammatus. When occurring in cumulonimbus, mammatus are often indicative of a particularly strong storm or maybe even a tornadic storm.
This was our second Mammatus Cloud sighting in Aurora above our house. The first was in June 2012.
We watched this set of clouds morph for a while. At one point, it looked as though all the "bubbles" were being pulled toward the bottom center of the mass.
They really are fascinating!