April 25, 2012
Weather Education Episode #9: Basic Formation of a Thunderstorm
RedOrbit Meteorologist Joshua Kelly
In this lesson, we are going to look at how a thunderstorm is created from the ground up.
The cumulus stage is the first stage in our life cycle of a thunderstorm. This is when the warm air from the Earth´s surface begins to rise upward into the atmosphere. The way this air is allowed to rise is known as lift. Lift is the upward motion of warm air towards a higher level in the atmosphere.
How high will this air go? To answer that, we need to understand a basic term known as saturation. Saturation occurs when an air parcel´s temperature is the same as the air around it.
For example let´s say we have an air parcel that has a surface temperature of 70 degrees F. This air parcel then rises up 1,000ft and will then cool down. This process keeps repeating itself until the rising parcel has found an equal temp. Once that equal temp has been found, the air parcel will then become saturated which leads to the formation of clouds.
In our Cumulus stage we have what is referred to as updrafts, meaning the air is being lifted upwards into the atmosphere.
The second stage is called the mature stage. During this stage we have both updrafts and downdrafts in the cloud. During this stage our cloud also becomes what is known as a Cumulus-nimbus cloud.
The updraft is still the warm air rising from the surface filling our CB cloud. The difference here is our downdraft. The downdraft is a combination of cooler air falling from the cloud towards the Earth´s surface in the form of hail, snow or rain, depending on the circumstances of the storm.
Each storm is different. Some storms will not have hail but just very heavy rain, while other storms will have very large hail and heavy rain both. Also, if the temperatures are just right, this downdraft can consist of snow. When this occurs we call it thunder-snow.
The last stage of our thunderstorm is known as the dissipating stage. Here we see that we now have downdrafts only, meaning our storm is no longer growing and is actually dying. But why?
To answer this question, we can look at it as a car. When you put gas in the car, it will continue to drive forward. This is the same as the warm air being fed into the thunderstorm. However, if you drive the car until there is no gas left, it will eventually stop. The same goes with a thunderstorm. If you cut off the warm moist air rising into it, eventually all the moisture will be gone in the storm leading to the cloud dissipating and the end of the storm.
These three stages are very important to understanding the basic of cloud formation and also basic thunderstorm formation.