Ominous Summer Thunderstorm Strikes Sydney, Australia

An intimidating looking thunderstorm rolled across Sydney, Australia yesterday afternoon, bringing with it flooding rainfall and intense lightning according to the Australian Bureau of Meteorology.

The awesome cloud everyone took a picture of is called a shelf cloud. Basically, the cold air descending out of a thunderstorm flows out ahead of the storm (called an "outflow"). As the outflow moves away from the thunderstorm, it takes on a half-dome/bubble shape as it rides along the surface.

As warm, moist air rides up along the colder, denser air in the outflow, it condenses along the top and creates a striking shelf cloud.

[Image by James Brickwood/Sydney Morning Herald]