HOUSTON, Texas  (KIAH) – A forecast can easily be busted by the strength of this atmospheric cap. When/ if it breaks can be the difference between hail, wind, and tornado producing supercell storms, or a warm sunny afternoon.  

In a capped environment, a layer of warm air aloft keeps storm activity at bay. As the day heats up warm updrafts form at the surface. Warm air rises! As you go up in elevation, the temperature decreases. We call this the adiabatic lapse rate; it changes by the amount of moisture present in the air. As long as the temperature keeps falling with height, air will continue to rise. If the updraft hits a layer of warmer air, it is then unable to continue moving upward to form larger clouds and storms. In this ‘capped’ environment storms DO NOT FORM.  

The ‘CAP’ explained: CW39 Weather

What causes the cap to break? 

If there is sufficient heating at the surface, or if there is an area where the ‘cap’ is weak enough, the cap can be busted through! This allows for strong storms to form. Clouds continue to build vertically allowing for large hail to form in the updrafts.  

Anvils are also formed by broken caps. Cloud tops continue to rise until reaching the bottom of the stratosphere. This causes massive storms to flatten and spread out at the top. The air there is so cold that the entire cloud top is made of ice particles. This gives the clouds a ‘wispier’ look compared to the cloud base.  

Summertime giant anvil cloud over Rapid City, SD.