Looking for a way to beat the heat and witness meteorology in action? Have a water balloon fight and while you’re doing so, chuck a full balloon up in the air and watch what happens as it spats on the ground (or your opponent).
You have just witnessed something similar to what is known as an outflow boundary originating from a thunderstorm. The balloon does not represent the rain but rather the cold air that can develop inside a thunderstorm. Just as warm air rises to create the thunderstorm that cold air will begin sinking out of the storm rather quickly and can even speed up if the rain starts evaporating as it sinks out of the thundercloud into drier air. There is only one thing that can stop that cold air from continuing to fall, the ground. Just as the water from the balloon spreads in all directions once it encounters a surface so does the colder air once it reaches the ground.
Spreading out in all directions this colder air becomes what is known as the outflow boundary and the precise location of the boundary can be detected in a number of ways. Temperature sensors can register a significant drop along with a wind direction change. Radar can show a light thin band moving away from the heavier storm as this wind picks up dust, insects, and even birds that are detected by the beam. The temperature change and different air densities also can reflect some of the beam back to the radar location. Referencing the picture shown you can also see clouds developing along the boundary with a visible satellite since it can act like a cold front. If conditions are right then that slight lift caused by the boundary can trigger more showers and storms restarting the entire process again.
It’s normally a hot and humid summer day with light wind where you may find these slow moving pop up thunderstorms that create situations like this. The outflow boundary often brings a nice cooler change to a hot summer afternoon as long as the storm creating it is not severe. Always be aware of where you are in relation to these types of storms since these boundaries can contain gusting winds and travel for miles away from the storm that caused it.