Explaining the atmospheric cap and severe weather

The atmosphere is just one of many spheres within the earth, but it’s also the sphere in which humans live and weather takes place. From calm, clear days, to stormy days, slight disturbances in the atmosphere drive our weather on a day to day basis, especially on days like today when roughly 50 million people are likely to see severe weather.

When it comes to severe weather you hear meteorologists across the nation talk about the infamous cap, especially on warm, sunny spring days.

To first understand the cap, you need to understand how thunderstorms develop. There are three key ingredients needed for them to form. The first ingredient is moisture, the second ingredient is instability and the third is lift, arguably the most important ingredient for thunderstorm development. Lifting is nothing more than a trigger that causes air at the surface to rise and this is where the cap can come into play.

If you were to look at satellite imagery on severe weather days, you are likely to see the cap in action. You’ll see cumulus clouds begin to develop, but they quickly fall apart before reaching thunderstorm potential and it’s all thanks to the cap, which is usually in the form of a temperature inversion (a layer of warm air above cooler air).

The cap forms because warmer air is less dense than cooler air, so it settles on top of the atmosphere forming a cap. The cap is basically a lid that is put on the atmosphere, much like putting a lid on a boiling pot of hot water. The pot resembles the lower level of the atmosphere, or the planetary boundary layer. During the likelihood for severe weather you hear that sunshine is bad and this has to do with the sun heating the surface of the earth, or heating up the water in the pot which causes it to boil. If there is no cap (lid), then the energy can freely escape. If a lid (cap) is put on the pot (atmosphere), then all the energy will be trapped in the pot and building up potential energy. This energy will increase over time and can eventually build up enough energy to punch through the cap and create strong to severe thunderstorms.

The cap can essentially make or break a forecast. If the cap stays in place then no storms will develop and vice versa.

Stay tuned to ABC 17 News as we continue to track the threat for strong to severe storms as we continue to head into the weekend.