Weather is all around us every day. Weather describes what the atmosphere is like on a particular day in a specific place. All weather happens in the troposphere.
Weather can be measured in many different ways. Air temperature, wind speed, wind direction, barometric pressure, humidity, and precipitation can all be measured to show what the weather is like.
Barometric pressure is the pressure in the atmosphere or how many air particles are around us. High and low pressure are caused by air temperature. Warm air rises and cold air sinks.
Warm air rises because as air molecules heat up, they expand. This makes them less dense than the air around them, so they rise. Cool air molecules shrink back and become more dense than the air around them, so they fall back to Earth.
High pressure is caused by cool air sinking because it brings more air molecules close to the surface of the Earth. Low pressure is caused by warm air rising because the air molecules move away from the surface of the Earth.
High pressure means there are a lot of air molecules around us. Imagine being in a room with a lot of other people, we would run into each other more often than in a room with just a few people. High pressure days are usually associated with sunny weather. This is because high pressure means the air around us in sinking. If air is sinking, water vapor can’t float up and form clouds.
On the other hand, low pressure means that there are fewer air molecules around us. When this happens, the air molecules are rising into the air. As they rise, they take the water vapor with them. The water vapor eventually joins together to form clouds. These clouds will produce precipitation.
Precipitation is a science word to describe all of the different forms of water that can fall from clouds: rain, snow, sleet, or hail. Precipitation happens when the water in clouds clumps together and becomes too heavy to stay floating in the sky. It falls down to Earth. The precipitation will be liquid if the air temperature is above freezing (0°C or 32°F), and will be solid if the temperature is below freezing.
The typical weather a place gets over many, many years is called the climate of that place. Climates can be hot and dry like in a desert or cold and wet like in a forest. There are many different climates all over the Earth.