You may recall hearing about a cap or a cap being in place when there is a chance for storms. But what is a cap exactly?
A cap is a layer of air aloft that is warmer or more dense than air below it. When storms or air tries to lift/float upwards to create a cloud or storm, it will run into this cap and be pushed back down, limiting or stopping the chance for storms to form. Think of a cap as the lid to a pressure cooker and the atmosphere is the cooker. At the surface (in the cooker) it’s hot and humid. Pressure (instability) starts to form and build. The lid (CAP) on the pressure cooker keeps all that pressure trapped inside at the surface. However, if too much pressure builds or the lid is weak (not secured corrected) the pressure building inside will blow the lid right off and all the steam explodes and rushes to the top of the room. This same process happens with storms. When air breaks through the cap if there is enough instability or pressure they will rapidly form thunderstorms.
Check out this visualization.
Meteorlogist,
Justin Storm
