Thunderstorms

Ever wonder how thunderstorms form? Did you know that there are multiple ways for thunderstorms to form?

Thunderstorms are fascinating weather phenomenon that have been documented since biblical times, several thousand years BCE. They’ve perplexed the Ancient Egyptians, philosophers of the Middle Ages, and brought many new fields in modern meteorology. To date there are thousands of different websites dedicated to severe weather ranging from government agencies to amateur storm chasers.

Below will be beginner level information on thunderstorm development and how it all happens.

The main process of thunderstorm development is warm air rising because it is less dense (as it rises it thins). It is less dense because warmer air (gases) have more freedom to move around making them “thinner” (think of ice, particles are frozen together tightly and can’t move). Warmer air is freer to move around and because of the force of gravity (among others), the more dense colder air sinks. This creates movement of air, the basic ingredient for thunderstorm activity. As shown below:

Clouds form up in the atmosphere where the warm air begins to cool. Clouds are moisture particles that are not yet heavy enough to come down. See the image below:

There are 3 stages of thunderstorm development once the clouds begin to form.

The cumulus stage is the early stage. The surface warms, the warm air rises, and forms clouds. The mature stage is when the clouds expand and are organized into structures with areas where precipitation, wind, lightning are released and also structures that help maintain thunderstorm formation. And then the dissipation stage occurs when the warm air supply is shut off and there is no more mixing and rising air.

There are several mechanisms by which air can get lifted into the atmosphere. Remember, thunderstorms form because of mixing of warm air and cold air. As the warm air expands and rises, it creates further cloud formation and precipitation.

Diving Deeper

Each small-scale location (say Philadelphia) has air that can be heated. As this piece of air rises, that’s when local cloud formation can happen.

Just for fun…

CAPE is the convective available potential energy which is essentially a measurement of how well the warm air can rise. It is the basic standard for severe weather in terms of a quick snap shot of greatest thunderstorm potential. If you look at a forecast graphic and see higher values of CAPE, chances are thunderstorms will follow. Shear below 2.5 KM AGL is essentially the change in wind speed between the surface and 2.5 kilometers above, this helps thunderstorms breathe and form into stronger thunderstorms. As you can see, there is a sweet spot for supercell activity and you can also see that seasonal climates impact thunderstorm formation.