Photo: Mark GallagherResembling something out of Independence Day, or the arrival of Cthulu, Mammatus Clouds are a meteorological phenomenon caused by sagging cellular accumulations produced in clouds of ice and water, and usually mean a fierce storm is trying to develop.
Tending to form in warmer months over the Midwest and eastern areas of the US, mammatus are nonetheless found elsewhere, as our chase across the States to track this singular meteorological phenomenon will reveal.
The above photograph was taken in Colorado, but Environmental Graffiti has a bunch of cool examples. The one from Tornado Alley state Oklahoma is particularly ominous.
[caption id="" align="aligncenter" width="462" caption="Photo: Wikipedia by NOAA"][/caption]