What is the concept of magnitude 8 thunderstorm and gale?

Thunderstorms with strong winds of magnitude 8 are generally considered to be the occurrence of broken branches in heavy rain.

The thunderstorm and gale of magnitude 8 represent the gale in the rainstorm. The wind speed of the eighth-grade gale is about 62~74 km/h, and that of the tenth-grade gale is 89 ~102 km/h. The wind speed of the eighth-grade gale can easily destroy trees and houses. On the whole, in the storm, branches are easy to fall on the street, which has a certain shock to the floor-to-ceiling glass of high-rise residential buildings.

According to the degree of influence of wind on ground objects, wind power is generally divided into twelve grades, generally six to eight grades are ordinary strong winds, and more than twelve grades are called typhoons or hurricanes. Wind force refers to the force exerted by the wind on an object. The greater the pressure difference between adjacent places, the faster the airflow, the greater the wind speed and the greater the wind force.

Thunderstorm and gale conditions

The collision of two air masses with different characteristics is a necessary condition for the formation of squall line. The most common situation is that a cold air mass collides with a warm air mass, but sometimes dry air collides with wet air. In either case, there will be wind shear in the sky. When the direction and speed of two adjacent winds are different, wind shear will occur. It can make the rising air leave the cloud top. Most squall lines begin with dry, dense cold air.

Although squall line belongs to mesoscale weather system, its formation and development are related to a certain large-scale weather situation. It mainly occurs in the warm area before the ground cold front 100 ~ 500 km.

Squall lines are generated in stratification with strong potential instability (see atmospheric static stability). This unstable stratification is mostly caused by the cold advection in the middle or upper layer superimposed on the warm and humid airflow in the lower layer. Squall lines are also related to high-altitude rapids, which often occur in areas where the vertical shear of rapids or winds is large.

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