Cumulonimbus Calvus With Pileus Belt

This growing cumulonimbus calvus tower sported a pileus belt at its middle as seen from Lininger Park in Marion, Iowa around 5:20 PM, Tuesday, July 26, 2011. Pileus are formed by strong updrafts acting upon moist air at lower altitudes. The pileus slowly migrated from left to right at the cloud's midsection. This calvus cloud was located about 22 miles to the east, in the Cedar Island/Morley/Olin area of Jones County. Cloud tops spiked above 55,000 feet.