While CAPE (when referring to weather) may not have the same definition as a superhero would use, in some ways, it does help give a thunderstorm superpowers.
CAPE is an acronym that stands for Convective Available Potential Energy. In other words, it’s the amount of fuel available to a developing thunderstorm. It’s an important number meteorologists use when determining the potential for severe thunderstorms. If the level of CAPE in the atmosphere is high, then that means the atmosphere is more unstable and could support severe thunderstorm development.
NOAA
CAPE is expressed in joules per kilogram (J/kg) and can range anywhere from zero to more than 5,000. There are no hard and fast rules when it comes to a magic number that will produce thunderstorms. For one, there’s more that goes into thunderstorm development than CAPE alone, however, a general rule of thumb is that anything less than 1,000 indicates very weak instability. If numbers are between 1,000 and 2,500, that would indicate moderate instability. Values between 2,500 and 4,000 would be strong instability and anything greater than 4,000 would be considered extreme instability.
A higher CAPE equals strong thunderstorm updrafts and can support larger hail as well.
This image shows where the higher CAPE levels are located within the atmosphere. Areas shaded in darker red show the highest level of CAPE.
However, depending on the location and the time of year, those values can be determined differently. For example, in the Plains, a value under 1,000 would be considered very weak instability in the spring or fall, however, it would be a little more impressive in the middle of winter.
So while there’s a sliding scale for CAPE and it’s just one tool in the toolbox for meteorologists, it does come in quite handy when forecasting the severe weather potential.
Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world’s biggest weather and climate stories for the last two decades.
