What does it mean when there is ‘cap’ in the atmosphere?

SIOUX FALL, S.D. (KELO) — We tend to throw around a lot of weather terms when talking about severe weather. Most are pretty well-known and self-explanatory, but a few require a bit of explaining. One such term is a “cap” in the atmosphere, which is a critical factor in severe weather forecasting.

At the surface, we have hot and humid air in place. That air typically will rise through the atmosphere into cooler temperatures, where condensation of that moisture happens, and clouds can form. At times, the temperature of the air will invert and increase with height instead of decrease. This is the aforementioned cap. The deeper the inversion layer, the stronger the cap and vice versa.

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As long as the cap is strong and remains in place, air cannot rise any farther. Vertical development, and by extension the potential for severe weather, is largely stopped. If the rising air can overcome the cap and break through, however, we can see at times rapid development of strong and severe thunderstorms capable of producing all varieties of severe weather.

Think of this like shaking a closed bottle of soda. As long as the cap is tightly in place, the air in the bottle can’t rise up and out. But if you loosen the cap enough, the air eventually escapes in a quick and at times explosive manner…just like what we see in the skies above KELOLAND.