Foreflight Radar symbology question

[AggieMike88]

DFW got a good long wet thunderstorm tonight. Been hot/dry for too long.

I took a look at the radar image on ForeFlight and spotted a symbol within the animation of the storm movement I didn't recognize.

What is the "line with dots" represent?

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[Rigged4Flight]

I seem to recall that as being a direction of the center of mass of the storm.

My memory sucks, so I could absolutely be wrong, but that's my (current) story, and I'm (currently) sticking to it.

 

[denverpilot]

http://blog.foreflight.com/2012/07/16/storm-tracks-now-available/

 

[flyingcheesehead]

And, the simple answer, from the link Nate provided:

The line and circles extend outward from the storm cell and predict where the storm could be in 20, 40, and 60 minutes.