A more or less violent squall, accompanying the passage of the cold front of a depression, distinguished by a sudden or rapid rise of the wind strength; a change of wind direction, a rapid rise of the barometer and a fall of temperature. There is usually heavy rain or hail, sometimes a thunderstorm or snow. The accompanying low black cloud forms a line or arch.
A squall advancing on a wide front caused by the replacement of a warmer by a cooler body of air. The passage of a well-developed line squall is usually marked by a sudden or very rapid change of wind direction; heavy rain, hail or snow, thunder and lightning; rapid rise in barometric pressure; a sudden fall of temperature; and violent vertical disturbances. A frequent characteristic is a long arch or line of low black cloud.
A sudden increase in wind speed, generally lasting from a few minutes up to half an hour. Line squalls are caused by instability of cold air moving over warmer water.