May 20, 2014

An updraft is the vertical (up and down) movement of air rising upward.  A mass of warm air will typically be less dense than the surrounding region, and so will rise until it reaches air that is either warmer or less dense than itself. The converse will occur for a mass of cool air, and is known as subsidence.   This movement of large volumes of air can create large clouds and is the main cause of thunderstorms.