All the conditions of the atmosphere are weather. Whether it’s hot or cold, dry or wet, sunny or cloudy, windy or still, it’s the weather. The weather is changeable from day today, and the total effect during a year is called the climate.
There are many complicated reasons for changes in the weather, but the most important influence is the sun. The sun’s heat evaporates water and warms the air so that rising currents of warm air carry water vapor into the sky.
There the air cools and the vapor condenses into rain. These things happen gently or violently. When they take place violently, we have storms. In Great Britain, there are approximately 200 weather reporting stations, and roughly the same number spread over the rest of Europe.
In addition, weather ships stationed in the Atlantic and special aircraft on regular patrol send back systematic reports on weather conditions. From this and other meteorological data weather forecasts are produced.
The maps which the weather experts study show them many things: places where the air pressure is equal, places of equal temperature, directions of local winds, cloudy or clear skies, rain or snow, the amount of rainfall, and regions where the air pressure is higher or lower than normal.
The weatherman can also tell from looking at the map what is likely to happen under the conditions that exist. He knows that low pressures indicate storms because cold air is moving in to replace warm rising air that is laden with moisture.
High pressures indicate fair weather. In the Northern Hemisphere, the winds around a high-pressure area blow outward in a direction similar to that followed by the hands of a clock. In a low-pressure area, they blow inward in a counterclockwise direction.
Thus the directions the winds will take can be predicted. The weatherman also knows how fast these pressure areas are moving across the country. Knowing all these things, and having reports of the weather in most parts of the country before him, the weatherman begins to get a pretty good idea of what to say about the weather that’s coming to our area!