Mammatus – Oh My!

Doug Wewer sent me some remarkable photos of mammatus clouds that he took at about 1 PM yesterday (May 8) on highway 191 just north of Rock Springs, WY.

Photos courtesy Doug Wewer

The name for mammatus or mammary clouds derives from the breast like lobes at the cloud base.    Schultz et al. (2006) called mammatus clouds an "enigma of atmospheric fluid dynamics and cloud physics" as they have rarely been the subject of detailed scientific investigation and remain poorly explained.  Since their article, there have been several papers on the subject, but a so called "unified theory" has yet to emerge.  Most mammatus events in the Intermountain West feature a dry, well mixed layer beneath cloud base and cooling produced by the mixing of moist and dry at cloud base and the sublimation (i.e., evaporation) of ice crystals falling out of the cloud may be important contributors in generating the convection that produces the lobes (Kanak et al. 2008; Kudo 2013).

There is a nice summary of the other proposed mechanisms on Wikipedia.  That article, however, argues that mammatus does not pose a threat to society, but I disagree.  Turbulence generated within and beneath mammatus is a concern for aviation safety, as discussed by Kudo (2013).