I frequently see lines like this (the red arrows in the image below point to what I am referring to) on doppler radars. They are usually propagating outward from a line of thunderstorms.

What are they, what do they indicate, and how do they form?

Doppler Radar Image

  • $\begingroup$ hard to say without more information but can be anvil blowoff theweatherprediction.com/habyhints2/388 $\endgroup$
    – user1066
    Commented Apr 10, 2020 at 4:08
  • $\begingroup$ Or simply a line of towering clouds or showers in elongation of what seems to be a divide between air masses that triggered the more vigourous convetion to the north east of that. $\endgroup$
    – user20217
    Commented Apr 10, 2020 at 19:57

1 Answer 1


If they propagate outward from thunderstorms, they are outflow boundaries. Cold air flows down from the thunderstorm with precipitation and spreads outward upon hitting the ground. This air moves ahead of the storm and forces warmer air upward, suspending clouds and other particles. That's what is visible on radar. More: https://en.wikipedia.org/wiki/Outflow_boundary


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