A single cell thunderstorm also can go by two other names: A pulse thunderstorm or an airmass thunderstorm. This type of storm only has one main updraft. It's a thunderstorm that goes through its life cycle and dissipates without creating any other cells, the term "cell" refers to the number of principal updraft points in the storm. Single-cell thunderstorms usually last between 20-30 minutes. They are usually poorly organized and seem to occur at random times and locations, making them difficult to forecast. Single-cells are rarely severe, They may contain heavy rain and can also produce occasional downbursts, small hail, and (rarely) weak tornadoes, storm chasers call these kind of tornadoes landspouts, but these are very rare in single cell storms. However, there is a special class of single cell that is always severe, I will discuss this special class later.
Radar image of bow echoes