I watched these spectacular clouds emerge and take over the northern skyline from Albuquerque today. Turn out these are known as mammatus clouds, and are no joke. They are awesome until the hail starts to pounding everything. Severe hailstorms have been a daily occurrence in varying parts of the state for the last week. Skylights are a common casualty of these storms as are car roofs. The roofs of houses can get be damaged as well - a roof inspector for hail-related insurance claims would not soon run out of work here. Crops aren't safe either and many gardeners cover their plots not just for shade but for hail protection in the summer time.
Mamma in latin means udder or breast, and these cloud features are arranged in a cellular formation hanging down from the undersides of various cloud species. "These patterns are formed from cold air sinking out of the main cloud body, which is most often cumulonimbus. Mammatus can be found under a large variety of other clouds as well, though not with the same consequences.
When associated with cumulonimbus clouds, mammatus are a strong indication of severe weather to come. This could be a particularly strong thunderstorm, heavy hail, or even tornado conditions. Due to dramatic temperature gradients, the wind shear can be intense at the boundaries, and present a danger to aircraft due to turbulence, and high ice content. Avoiding them may be hard, however, since these formations can stretch hundreds of miles across the skies.