What is an outflow boundary?

WEATHER: Like It or Not!
CHICAGO (WLS) -- Have you heard of the term outflow boundary? It's a feature of a thunderstorm that we can see on Live Doppler 7 Max Radar, most often in the summer.

On a radar image, you can see the storm in red, but there's this thin green line rushing out ahead of the storm. That's the outflow boundary.

In some thunderstorms, rain-cooled air sinks out of the storm and hits the ground. That rain-cooled air then spreads out away from the storm and creates almost like a mini cold front, called an outflow boundary.

As that mini front or outflow boundary runs into warm, humid air, it can force that warm air to rise. Cold air is denser than warm air, so cold air sinks and warm air rises.
If that warm air rises high enough and fast enough, a new storm can develop on the outflow boundary.

When you see these type of signatures on the radar, it often means storms can pop up in random places away from the original storm.

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