CAPE stands for convective available potential energy. Essentially, CAPE is a measure of the instability in the atmosphere which is one of the main ingredients for severe weather. Warm, moist air near the surface, combined with cooler, dry air aloft causes "instability". This instability helps provide lift and moisture for convection, or thunderstorm development. Without convection, thunderstorms would not develop. Tornado development usually requires a significant amount of instability in order to develop supercells or other forms of convection. Many other factors, though, are necessary for tornado development. Wind shear (changes in direction and speed of winds with height) is critical, among others. I have noticed in recent years that tornadoes have formed many times in situations where instability values were not impressive but shear and other factors were strong. Case in point: the Huntsville tornado of January 21, 1010.
I have been posting about Alabama weather on this blog since April 2006. Here you will find my observations, information provided by the NWS, links to quality weather information from other sources, and historical weather data. Please "follow" me on Twitter and join my "fan" page on Facebook. Twitter and Facebook posts are usually more current/breaking news. I appreciate your visit. Enjoy and come back soon. Thank you!