Caught in the heat of traffic after the surge of a storm, Echo-reader Erika Nehil-Puelo snapped these phone photos outside of Chicago’s downtown.
Despite their eerie look, the pouchy cloud formations often signal the passing of a severe storm, as was the case in Chicago.
The orb-like mammatus clouds hang from the bottom of other cloud structures, most commonly cumulonimbus. Their smooth, drooping appearance is attributed to convection of the air, the tendency of colder denser material to sink.
Mammatus can form fields, with lobes organized into nearly-equal lines. Other times, mammatus appear to have no organization, forming in unequal clusters, as shown.