Almost everyone has heard the expression "the calm before the storm." It is usually used to describe a peaceful period just before a very stressful situation or a tense argument.
British sailors coined the phrase in the late 1600s; they noted that before certain storms the seas would seem to become still and the winds would drop.
Science has given us the reason. According to US website HowStuffWorks, a calm period occurs because many storms, tornadoes and hurricanes draw in all the warm and humid(湿热的) air from the surrounding area. As this air rises into the storm clouds, it cools and acts as "fuel for the storm, like petrol in a car". Once the storm has taken all the energy it can from the air, it is pushed out from the top of the storm clouds and falls back down to ground level. As the air goes down, it becomes warm and dry. Warm and dry air is stable, so once it covers an area, it causes a calm period before the storm. This same process also causes the "eye of the storm" in hurricanes and tornadoes. In these conditions, the calm occurs in the center of the storm because of the strong rotating (旋转的) winds.
The Weather Network has a tip for working out how far away a storm is. First count how many seconds there are between a flash of lightning and a clap of thunder, roughly three seconds equal one kilometer. So, for example, if you count nine seconds, the storm is about three kilometers away. A good method is that if your count is below 30 seconds, you should seek shelter straight away.
However, due to the complexity of storm system, not all storms take place after calm. Given the right conditions, some storms announce themselves with heavy rain and fierce winds.
So, your best bet is to keep yourself updated with weather reports for any predictions regarding a coming storm in your area. That's the most reliable way to predict the next display(展示) of nature's temper (脾气).
