What is a squall line? What weather does the squall line weather system cause?

Squall line is a linear strong convection, and its length-width ratio generally exceeds 5: 1. The weather is generally bad and disastrous, such as strong wind, short-term heavy precipitation, hail and so on. And there may be a tornado.

Baidu Encyclopedia explains as follows:

Squall line (English: squall line), sometimes called line squall line. It refers to small and medium-scale strong convective weather with sudden changes in wind direction and wind speed, usually accompanied or preceded by a cold front. This is very destructive. The squall line mostly travels from cold air to warm and humid wetlands, which leads to the pattern of upper cold and lower warm, which makes the thermal structure of troposphere different and produces strong convective weather. Thunderstorms on squall lines are usually composed of several thunderstorm cell, so they can produce drastic weather changes. At the beginning of the 20th century, squall line was often used as a synonym for cold front. The typical phenomena of squall line transit are sudden change of wind direction, sharp increase of wind speed, sudden increase of air pressure and sudden change of temperature. In its heyday, the average wind force was above 10, and the gust was above 12. At the same time, it may be accompanied by thunderstorms, heavy rains, hail, strong winds, tornadoes and sea tornadoes. Squall lines usually have typical bow characteristics, accompanied by strong straight wind. When there is a mesoscale low pressure area, there may be a tornado along the wavy linear echo. In summer, the bow echo may develop into a super convective storm and pass through a large area at a very high speed. The trailing edge of the rain shield is usually accompanied by a mature squall line, with low wake pressure, and sometimes even accompanied by a thermal storm. The horizontal range of the squall line is very small, the length is usually only 150~300 kilometers, the width is only half a kilometer to dozens of kilometers, and the height is only about 3 kilometers. Its maintenance time is generally 4~ 10 hour.