Daniel Swain in The Smithsonian Magazine

Although photographs of the event’s aftermath testify to tall hail drifts throughout the city, these monoliths were created by urban flash floodingthat sent ice flowing into streets and culverts, not purely through accumulated ice dropped during the storm, as climate scientist Daniel Swain of the University of California Los Angeles explains on Twitter. (Similar occurrences have previously been recorded in Mexico City and the Texas Panhandle, among other locations.)