Weather

Weather refers to the state of the Earth's atmosphere at a specific place and time. We describe it using temperature, humidity, cloud cover, and stability. Weather includes changes in temperature, precipitation, and other conditions from day to day. Weather looks at short-term changes, while climate describes average conditions over longer periods.

Weather is driven by differences in air pressure, temperature, and moisture in different places. These differences come from the Sun's angle, which changes with latitude. This leads to large patterns of air movement, such as the Hadley cell, Ferrel cell, polar cell, and the jet stream. Because Earth's axis is tilted, sunlight hits different parts of the planet at different angles during the year, affecting weather patterns.

Weather forecasting uses science and technology to predict future conditions. Because Earth's weather system is a chaotic system, small changes can cause big effects. People have tried to control the weather throughout history. Studying weather on other planets, like Jupiter's Great Red Spot, helps us learn more about our own planet's weather.

Causes

On Earth, common weather phenomena include wind, cloud formation, rain, snow, fog, and dust storms. Larger events such as tornadoes, hurricanes, typhoons, and ice storms are also part of Earth's weather system.

Weather happens mainly because of differences in air pressure, temperature, and moisture. These differences are caused by how directly the sunlight hits a place, which changes depending on where you are on Earth. The contrast between cold polar air and warm tropical air creates air movements, like the jet stream. These movements influence weather patterns far away. Small changes in the atmosphere can lead to big changes in the weather.

Shaping the planet Earth

Weather is one of the key processes that helps shape our planet. It breaks down rocks and soils into smaller pieces through a process called weathering. When it rains, water droplets pick up carbon dioxide from the air, making the rainwater slightly acidic. This acidity helps water wear away surfaces over time. The tiny bits of rock and chemicals washed away can later form new rocks and soils, showing how weather helps change the Earth’s surface.

Effect on humans

Further information: Biometeorology

Weather is something everyone feels when they step outside. People often talk about how the weather changes.

Sometimes, very strong weather, like tornadoes, can damage buildings and make life hard for people.

Weather has also played a part in big moments in history. For example, strong winds helped protect Japan long ago. Hurricanes have sometimes changed where families live, like after Hurricane Katrina in 2005, which caused many people to leave the Gulf coast. Very cold times, such as the Little Ice Age, made it hard for farms to grow food in places like Europe and Finland.

Forecasting

Weather forecasting is the science of guessing what the weather will be like in the future at a certain place. People have tried to guess the weather for thousands of years, but today we use computers and science to make better guesses.

We collect information about the air right now and use what we know about how air moves to figure out what will happen later. Even with powerful computers, it’s hard to be exact because the air changes in complicated ways. That’s why forecasts are more accurate for the next few days than for a week or more away. People use weather forecasts for many reasons, like knowing if they need an umbrella or planning farm work.

Modification

People have always wanted to control the weather. Ancient cultures did special rituals to bring rain for their crops. Today, people try things like cloud seeding to clear fog at airports, bring more rain to mountains, and stop hail.

Human activities can change the weather without planning to. Factories send out pollutants that cause acid rain, which hurts lakes and plants. Emissions of greenhouse gases help cause climate change. This can lead to more extreme weather like floods and storms. Big cities can even make their own weather by heating the air around them.

Microscale meteorology

Microscale meteorology is the study of very small weather events. These events happen over short distances, usually less than 1 km. Examples include tiny cloud "puffs" and other quick changes in the sky. These small weather patterns are too tiny to appear on a weather map.

Extremes on Earth

Main articles: Extremes on Earth and List of weather records

Earth has many different temperatures. The coldest temperature ever measured was −89.2 °C at Vostok Station in Antarctica in 1983. The hottest temperature ever measured was 57.7 °C in Libya in 1922.

Some places on Earth have very strong weather. In Antarctica, winds can blow very fast, up to 199 miles per hour. Mount Rainier in Washington, US, got the most snow in one year, with over 31,000 mm of snow.

Extraterrestrial weather

Studying weather on other planets helps us learn more about Earth’s weather. These planets follow similar rules but have very different conditions. For example, the Cassini–Huygens mission to Titan found clouds made from methane that create rain of liquid methane.

One famous feature is Jupiter’s Great Red Spot, a huge storm that has lasted for over 300 years. On planets like Neptune, winds can blow much faster than on Earth. Scientists are still learning why these distant worlds have such extreme weather.

Space weather

Main article: Space weather

Weather isn't just something that happens on Earth—it can also happen in space! The Sun sends out a stream of particles called the solar wind, which travels through the Solar System. Sometimes, big events on the Sun, like coronal mass ejections, send even more particles out. These space weather events can create beautiful lights in the sky called aurorae, and they can sometimes affect things like electricity grids and radio signals. Scientists study these space weather patterns to learn how they impact our planet.