Here we see a simulation of a thunderstorm, which develops from a small thermal (i.e., a local patch of relatively warm air) in an unstable atmosphere. As the warm and humid patch of air rises, it expands and cools, water vapor condenses releasing heat, which make the bubble even more buoyant. The rising patch of air draws surrounding air upward, which also becomes ever more buoyant. This runaway cycle drives the thunderstorm. Initial wind speed and direction varies with altitude in a fairly realistic way, which gives the resulting storm its classic anvil shape. Two movies are played in succession: the 1st shows cloud+ice water, which is what you typically see in such a cloud; the 2nd is the magnitude of vorticity, which shows wind shear, turbulence, and tornadoes. Notice how the rising thermal draws up ground wind shear, and how the storm splits into two counter-rotating pieces.

This simulation was performed by the Woodward research group (Dept. of Astronomy, U. of Minnesota), using the NCOMMAS thunder storm code originally developed by Louis Wicker at the National Oceanic and Atmospheric Administration's National Severe Storms Laboratory in Norman, Okla.. The code was adapted to run in parallel by the Woodward team. This movie was produced with Hierarchical Volume Rendering (HVR) software (www.lcse.umn.edu/hvr) run on a PC rendering cluster in the Laboratory for Computational Science and Engineering (LCSE) at the U. of Minnesota.