We often get asked during tours, what are the different types of thunderstorms we will encounter? The answer to that question is what we’ll discuss in the following article. Many storms you will see while on tour can be quite pretty and also violent, and knowing these different storm types can help you understand the atmosphere a bit better. During your tour with us, we’ll conduct basic “weather 101” classes which will further help you understand how the atmosphere works. Every thunderstorm has two main parts, the updraft and the downdraft. The updraft is that popcorn ball looking cloud which shows water vapor rising and condensing in the atmosphere. The downdraft is that area of the storm where rain, hail and cool winds occur. These two parts vary tremendously in every storm, but the key is that they both are always present in a thunderstorm.
First it is important to understand the “ingredients” needed to have a severe storm develop. A simple acronym to keep in your mind is SLIM. This stands for Shear, Lift, Instability, and Moisture. Without these ingredients the chance of a severe storm are “slim”. Shear takes the form of two different types: speed shear, which is an increase in wind speed with height, and directional shear which is a change in wind direction with height. Both of these types cause a storm’s updraft to tilt and rotate, helping it to last for many hours. Lift is created by either fronts, mountains, the sun causing thermals to rise or any situation where winds converge, or come together causing the air to rise. Instability is created through various processes that cause the atmosphere to become unstable. We measure instability through what is referred to as Convective Available Potential Energy, or CAPE. Finally moisture is measured by the dewpoint. That is the temperature where the air becomes completely saturated and condensation occurs. You can have various amounts of these ingredients and get severe storms, but all 4 must be present to get a storm to become the most violent thunderstorm on earth, the supercell.
Ok. Let’s discuss the different types of storms.
Pulse storms, or the typical “garden variety” thunderstorm, occurs on those lazy summer or spring days in the late afternoons. These storms are short lived due to the nature of the environment they form in.
They can occasionally produce strong winds and hail, but rarely have the ingredients to produce much more than that. They look like they are standing straight up, and in reality, they are. Very little shear causes the updraft to stand upright, and as rain & hail falls it falls directly INTO the storm’s updraft, effectively killing it. Most pulse storms last less than an hour.
Multi-cell storms can also form in an environment where there is little shear, but enough lift to cause numerous storms to form either in a line or a cluster. These storms, as the name implies, have multiple updrafts and downdrafts, which compete for available CAPE. They can become severe and usually produce more wind as they collapse, and possibly hail. Again, these storms also rarely produce tornadoes. Multi-cell storms can form along a boundary and eventually move downwind where a better environment may occur and transition into supercell storms.
The supercell is the most violent and long lived thunderstorm type in the world. They form in an environment where all the ingredients (SLIM) are present and can persist for 8-12 hours! They are responsible for the majority of severe weather that occurs and also the vast majority of tornadoes.
Supercells can look like spaceships or a “stack of plates” and can be very electrified. Seeing one of these monsters is a treat, and watching its lifecycle is an amazing thing to see. It seems as if they are alive and often do what they can to survive as long as possible. All major violent tornado outbreaks occur from these types of storms. They can also produce hail the size of softballs or even larger! This type of storm is the one we hope to have the pleasure of witnessing the most on tour, however all types of storms are quite pretty.