What is Weather?
Weather is sunny, rainy, snowy, windy and stormy. That’s what’s happening outside right now. The weather is different in different places on the planet. In some places it is sunny, while in others it is snowing. Many things affect the weather, including the atmosphere, the sun, and the season.
The science of time is called meteorology. Meteorologists study the weather and try to predict it. Predicting the weather is not easy because there are so many factors and variables involved.
Different parts of the world tend to have different weather patterns. Some places, such as San Diego, California, are sunny most of the year. While other places, such as the rainforest, get the most rain per day. Still other places are cold and snowy most of the year, such as Alaska.
What is Wind?
Wind is the result of the movement of air in the atmosphere. Wind is caused by differences in atmospheric pressure. Cold air is heavier than hot air. More fresh air will create an area of high pressure. A large amount of hot air will create an area of low pressure.
When low pressure and high pressure meet, the air will want to move from the high pressure area to the low pressure area. It creates wind. The larger the temperature difference between the two areas of pressure, the faster the wind blows.
Wind on the Earth
On Earth there are often regions of high pressure near the poles where the air is cold. There is also lower pressure at the equator where the air is warm. These two main areas of atmospheric pressure keep the wind in constant motion around the Earth. Earth’s rotation also affects wind direction. This is called the Coriolis effect.
Precipitation (Rain and Snow)
When water falls from the clouds, it is called rain. It can be rain, snow, sleet or hail. Rain is formed from the water cycle. The sun heats the water on the Earth’s surface. Water evaporates into vapor and moves through the atmosphere. When water condenses, clouds form. Eventually, the water droplets in the clouds become large and heavy enough for gravity to bring them to the ground as rain.
We get snow when the temperature is below freezing and small ice crystals stick together to form snowflakes. Each snowflake is unique, so no two snowflakes are alike. Hail often forms during heavy thunderstorms, where balls of ice are blown repeatedly into the frigid atmosphere. Every time another layer of water on the ice ball freezes, the ball gets bigger and bigger until it finally falls to the ground.
Clouds
Clouds are small drops of water in the air. They are so small and light that they float in the air.
Clouds form from condensing water vapor. This can happen in many ways. One of them is when warm air or hot front meets cold air or cold front. The hot air will be pushed up and into the cooler air. As the warm air begins to drop in temperature, water vapor condenses into liquid droplets and forms clouds. Also, warm and humid air can blow into a mountain. The mountain will push air up into the atmosphere. As this air cools, clouds form. That is why the top of the mountain is often cloudy.
Not all clouds are the same. There are three main types of clouds called cumulus, cirrus, and stratus.
Cumulus – Cumulus clouds are large, porous white clouds. They look like floating cotton. Sometimes they can turn into massive cumulus clouds or towering cumulus clouds. These clouds are storm clouds.
Cirrus – Cirrus clouds are thin, tall clouds made of ice crystals. They usually mean good weather is on the way.
Stratus – Stratus are low, flat clouds that tend to cover the entire sky. They give us “overcast” days and may drop light rain called drizzle.
Fog – Fog is a cloud that forms over the Earth’s surface. Fog can make it difficult to see and dangerous to drive, land an airplane or steer a train.
Weather Fronts
A weather front is the boundary between two different air masses, the warm air mass and the cold air mass. There is often stormy weather on a weather front.
A cold front is where cold air meets warm air. The cold air will move under the warm air forcing the warmer air to rise rapidly. Because warm air can rise rapidly, cold fronts can cause cumulus clouds to form with heavy rain and thunderstorms.
A hot front is where hot air meets cold air. In this case, the warm air will slowly rise above the cold air. Warm fronts can cause light rain and drizzle for extended periods of time.
Sometimes a cold front can overcome a warm front. When this happens, it creates an obscured front. Clouded fronts can produce heavy rain and thunderstorms.