Have you ever been outside on a sunny, hot and humid summer day, then out of nowhere there's a thunderstorm that lasts for 30 minutes? As quickly as the storm arrived, it dissipates leaving you with sunshine again. If this is the case, it is likely that you were under a single cell thunderstorm! They are pretty common during the summer months and can occur almost anywhere in the Midwest and Northeast.
Most single cell thunderstorms regularly develop from two things; a sea/lake breeze, or an outflow boundary. A sea/lake breeze is the cooler air from a sea or lake moving on-shore and reacting similarly to a cold front. Likewise, an "outflow boundary" is a boundary from nearby storms releasing their own cool air, which acts the same as sea/lake breezes. Both mechanisms undercut the hot and humid land air, forcing the soupy air to rise. This rapid rise creates instability and localized thunderstorms with brief heavy rain develop.
These types of storms typically last less than an hour, but can result in areas of minor flooding and isolated wind damage. As these storms go through their "phases of life", they usually do not move much and dump heavy rain over the same location before evaporating. The image below demonstrates the phases for single cell storms. The developing stage is the first step with a storm, as a regular cumulus cloud becomes very tall. As the clouds continue to grow, it eventually reaches its mature stage, when updrafts become stronger, rain is produced, and the strongest winds typically occur. Most of the time, heavy rain is the main concern, however damaging wind gusts occasionally appear with these storms. With the lack of wind shear aloft or a stronger lifting mechanism (like a low pressure area or an upper level disturbance to sustain the storm), the cell weakens and begins to evaporate which marks the end of the single cell storm.
However, as this storm evaporates, the term "outflow boundary" comes into play. The wind from the storm moves outwards like a ripple in water, and can result in other storms developing just a few miles down the road. This cycle can continue through the afternoon until the sun sets and daytime heating from the sun dissappears.
