What causes a squall line to break apart

[shane turner]

I am just curious to know what causes a squall line to break apart and become individual supercells. There have been several occassions where I have seen squall lines break apart and become individual supercellls and then it goes back and forth between a squall line and supercells. It would make me wonder during tornado outbreaks if there was going to be a lot of tornadoes or go linear. It seems like it has happened on occassions when there was a pretty good sized tornado outbreak and numerous wind and hail reports with the squall line.

[Greg McLaughlin]

I wonder if there have been any F5 tornadoes with embedded squall line supercells?

[Jeff Duda]

I believe this has something to do with the orientation of the shear vector to the squall line. Shear vectors oriented more perpendicular to the line tend to favor discrete cell development, whereas a shear vector parallel to the line tends to favor a linear mode.

[Paul Knightley]

There are a number of things which can cause a line of storms to break up, as there are when you consider isolated storms which decay as well. One of the main ones is obviously a reduction in instability, as it runs into cooler air, or drier air. Also, if the upper trough which may be helping to force the line overruns it, upper subsidence can kill it off.