What is a thunderstorm?

Most thunderstorms consist of cumulonimbus clouds. The coverage of each cumulonimbus cloud is generally only a few kilometers in diameter and about ten kilometers in height, which looks like a tower in the air from a distance. The life span of a cumulonimbus cloud is generally only one or two hours.

In the vicinity of active weather systems such as trough of low pressure, cumulonimbus clouds can be produced continuously, and the impact of thunderstorms is great and lasting. Some cumulonimbus clouds will combine to form particularly strong thunderstorms.

On sunny days in summer, the heat of the sun during the day may also stimulate the formation of cumulonimbus clouds and form thunderstorms. The impact of these thunderstorms is very small and short-lived, and it may be sunny not far from thunderstorms. Cumulonimbus clouds sometimes drift with the wind, affecting other areas, and the areas where cumulonimbus clouds are produced may also change with time.

Lightning and thunder are the characteristics of thunderstorms. In an unstable and humid atmosphere, water droplets and ice particles in the clouds generate charges in convection activities. When the voltage formed by charge accumulation is too large, lightning discharge will occur between clouds or between clouds and ground, and the air around the discharge channel will expand rapidly, resulting in rumbling thunder. To put it simply, thunder is heard three seconds after seeing lightning, which means that the thunderstorm is about one kilometer away from the observer, and the real distance is calculated in proportion to the length of time.

Rainstorms, lightning and strong winds are often accompanied by thunderstorms. Sudden heavy rain will bring danger to outdoor athletes. Lightning may damage power facilities and cause fire; Or death or injury caused by electricity. In addition to direct lightning, electrical appliances that touch conductors or are affected by lightning can also get electric shock. Thunderstorms often have strong winds or violent gusts, and the wind speed suddenly increases or the wind direction suddenly changes. In Hong Kong and its adjacent waters, ships were sunk by thunderstorms and strong winds. On the other hand, the wind shear caused by thunderstorms and strong winds also poses a threat to the safety of aircraft taking off and landing.

Under some favorable circumstances, thunderstorms may appear in the form of funnel clouds accompanied by strong columnar vortices. When the vortex touches the ground, it is called a tornado, and when it touches the ocean, it is called a waterspout. The air pressure near the center of the vortex is very low and the wind is very strong. When a tornado passes by, thin buildings may be damaged by strong winds and indoor and outdoor air pressure differences, and trees and cars will be blown up. At sea, a small boat once encountered a waterspout and sank. Tornadoes and waterspouts after landing have caused damage to buildings in Hong Kong, although this is rare.

Hail is a hard ice particle, usually only a few millimeters in diameter, and occasionally there will be bigger hail. Hail is produced in fully developed cumulonimbus clouds in thunderstorms, mainly in spring. Heavy hail will destroy crops and break windows, greenhouse glass and car windshield.

Matters needing attention in thunderstorm weather

Stay indoors. People who work outdoors should hide in buildings.

Do not swim or do other water sports. Get out of the water and find a place to hide.

Avoid using phones with plugs or other electrical appliances, including computers.

Do not touch antennas, faucets, water pipes, barbed wire or other similar metal equipment.

Avoid taking a shower with a shower.

Do not handle flammable items in open containers.

Don't stand on the top of the mountain or near objects with high conductivity. Trees or masts are easily struck by lightning and should be kept as far away as possible. After lightning strikes an object, the current will spread through the ground, so don't lie on the ground. Wet ground is especially dangerous. You should squat down to minimize the contact area with the ground.

Hikers and other outdoor activities should carry radios with them and pay attention to the latest weather news of the Observatory.

Always pay attention to the possibility of heavy rain, and don't stay in rivers, streams or low-lying places.

Motorists should be careful of strong winds when driving on expressways or overpasses.

Small boats at sea should be careful of strong winds or waterspouts.

If you encounter a tornado, you should immediately hide in a solid building. Stay away from the window, squat on the ground, and protect your head with your hands or thick pads. If you are outdoors, stay away from trees, cars or other objects that may be blown up by tornadoes.