Instability line

From Glossary of Meteorology

instability line

(No longer frequently used.) Any nonfrontal line or band of convective activity in the atmosphere.

It is a general term and includes the developing, mature, and dissipating stages. However, when the mature stage consists of a line of active thunderstorms, it is properly called a squall line; therefore, in practice, instability line often refers to the less active phases.
See also pseudo front, prefrontal squall line

Fulks, J. R. 1951. Compendium of Meteorology. 647–652.

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