A series of squalls, in which the wind speed increases by up to 50 per cent then dies away gradually, associated with very vigorous cumulonimbus clouds that merge to form a continuous line up to 1000km long and advance at right angles to the line. The line begins to form ahead of a cold front that is advancing beneath warm, moist air. Each storm cloud lasts for only an hour or two before exhausting its supply of moisture and dissipating, but the gust front produced by cold, subsiding air leaving the cloud undercuts warm air ahead and to the right of the cloud, triggering the formation of a new cloud. The squall line becomes detached from the cold front and advances ahead of it into the warm air.
Subjects: Ecology and Conservation.