Altitude
Altitude is another word for height. When you are flying in an aeroplane, you are at a higher altitude than when you are on the ground. If you climb a mountain, you are at a higher altitude at the top than at the bottom. Altitude can be measured in metres or in feet, and starts from sea level — which is the surface of the ocean. If you are at sea level, you are at zero altitude.
Atmosphere
The atmosphere is all around us. It is the air we breathe. It is a layer of air which covers the whole of Earth. It is several miles high, and beyond the atmosphere is space.
Autumn
The autumn months are September, October, November. Autumn is when it starts to get cooler and less sunny. There is less daylight in the autumn. In autumn many plants stop growing. Many leaves turn yellow and brown and fall from the trees in autumn.
Avalanche
An avalanche is a sudden heavy fall of rocks or snow down the side of a mountain. Avalanches are one the biggest dangers in the mountains to life and property.
Blizzard
Blizzards happen when there is heavy snow and strong wind. They are very cold and can be dangerous. This is because so much snow falls you cannot see very far and people sometimes get lost or cannot find their way home.
Climate
Climate is the word we use for weather over a long period of time. The desert has a dry climate, because there is very little rain. The UK has a 'temperate climate' which means winters are, overall, mild and summers, generally, don't get too hot.
Clouds
Clouds are made of lots tiny drops of water that float in the air. Clouds can be white, grey or dark grey. The darker a cloud, the more water it is carrying, and the more likely it is to drop that water as rain, snow or hail. Clouds float because the water in them is warmer than the air around them. Clouds can be different shapes, but have three main types. Cirrus clouds are white, thin and wispy. Cumulus clouds are white and fluffy like cotton wool. Stratus clouds are grey and cover the whole sky.
Condensation
You might have seen the effects of condensation before, such as when a car window steams up. This is because tiny, invisible drops of water float around in the air, this is called vapour. When vapour in the air gets colder it changes from being a vapour into a liquid which we can see. It happens on car windows because they are often colder on the outside, and so vapour turns into water as it touches the glass. Another way to see condensation in action is to take a bottle of water from a fridge and leave it out in a room for a few minutes — a thin layer of water will form on it. This is because the vapour in the air cools as it touches the cold bottle, causing condensation.
Drought
Droughts happen when it does not rain for a long time. This makes the land dry. Lakes, ponds and rivers run low. People have to use less water when there is a drought to make sure there is enough to drink. Hot countries often suffer droughts.
Evaporation
Puddles left after it has rained slowly disappear. This is because of evaporation, which happens with all water, even the oceans. Evaporation happens when water is heated up by the sun. The water turns into vapour — tiny droplets of water which float on the air. As a whole puddle is slowly turned into vapour, eventually it dries up. Evaporation is the opposite of condensation.
Fog
Fog is the same as cloud but on the surface of the ground. Fog makes it difficult to see very far ahead. Planes can’t land or take off in fog. Travelling on roads in fog can be very difficult.
Frost
Frost is white ice crystals that cover surfaces, such as grass or roofs, when the air is very cold and the sky is clear of clouds. Frost can be slippery. Most of the frost we get is in the winter months.
Humidity
Humidity is how damp the air feels. There are always tiny droplets of water called water vapour floating in the air. Humidity is a measure of the amount of water vapour in the air. Weather forecasters need to know the humidity because it helps them predict rain and fog.
Hurricane
Hurricanes are tropical storms with very strong winds and heavy rain. They usually affect warmer parts of the world, such as the Caribbean and the coast of North America where the sea temperatures are higher than 26 °C. They can cause lots of damage as they pass over land, with thunderstorms and tornadoes at times. Tropical storms are also known as cyclones or typhoons in other parts of the world. We don't get hurricanes in the UK, but we do sometimes get very strong winds which can be called hurricane force winds (more than 64 mph).
Lightning
Lightning is a large flash of electricity from the sky to the ground. It happens when there is a thunderstorm. Lightning is very dangerous and as much as six times hotter than the sun.
Meteorology
The study of the atmosphere and all its elements, including weather and how to forecast it.
Mist
Mist is a type of fog.
Monsoon
A seasonal wind, found especially in Asia that reverses direction between summer and winter and often brings heavy rains.
Ozone
About 19-30 kilometres above the Earth is a layer of gas called ozone, which is a form of oxygen. Ozone reflects harmful rays from sunlight back to space.
Precipitation
Precipitation is a name for water falling from the sky. It is normally rain, but when it is cold, it can fall as snow or hail or sleet.
Rain
Rain is drops of water that fall to the Earth from clouds in the sky. Rain is important because it gives us fresh water for plants to grow and animals to drink. The amount of rain is measured using a rain gauge.
Rainbows
Rainbows are beautiful arcs of colour in the sky. When the sun shines through rain we get rainbows. The seven colours of the rainbow are; red, orange, yellow, green, blue, indigo and violet.
Seasons
Seasons are changes in the weather where we live, caused by the Earth being closer or further away from the Sun. There are four seasons in a year; spring, summer, autumn and winter.
Snow
Snow is a number of ice crystals joined together. No snowflake is the same. Snowflakes are white because they reflect sunlight (which is white). It is never too cold to snow. Most of the snow in the UK falls in the winter.
Snow drifts
Snow drifts are deep areas of snow. Sometimes they can be several metres deep. They happen when the wind blows snow into big piles.
Spring
The spring months are March, April, May. Spring is when the Earth starts to warm up and plants start to grow.
Summer
The summer months are June, July, August. Summer is when we feel hot and sticky. The sun shines more and for longer in the summer.
Sun
The Sun is a star. The Sun is a star a long way away in space (93 million miles). It gives us daylight and warmth and allows life to survive on Earth. Weather stations measure the hours of sunshine using special instruments.
Temperate
Temperate is similar to mild. It means not too hot, and not too cold. The UK is said to have a temperate climate, because it does not have extremes of weather.
Temperature
Temperature is a measure of how hot or cold it is. Thermometers are used to measure the temperature.
Thunder
Thunder is the sound that follows a flash of lighning.
Transpiration
Plants get water from the ground to help them grow. Some of this water comes out of their leaves and goes out into the air. This is transpiration. It is like plants breathing.
Water Cycle
The water cycle is a way in which water moves around the world. Without it, nothing would grow and humans would not be able to live. It starts in the ocean, where the heat of the Sun turns sea water into vapour, tiny droplets of water which float in the air - this process is called evaporation. Water vapour rises into the sky to make clouds. The wind blows the clouds over land and they drop their water as rain, sleet or snow. This falls on the land as water, which allows plants to grow and gives us drinking water. Much of the water then flows into lakes and rivers, and is carried back to the sea. Then the process begins again.
Weather
Weather is all around us. If you look outside, you will see it is sunny or cloudy. It may be dry or wet. It may be calm or the wind may be blowing. It may be cold or warm. All these things are the weather. What is the weather doing outside your window?
Weather Forecast
You can see weather forecasts on the television and hear them on the radio. You can look at them on the internet or in newspapers. They tell us what the weather is going to be like today, tomorrow, and sometimes even further ahead. Experts make them by using their knowledge of the weather and special equipment to predict what will happen next. We need weather forecasts to help plan our lives. If it is going to be hot and sunny, we can plan to go swimming. If it is going to be very cold, we can wrap up warm. If it is going to rain, we can take an umbrella.
Weather Satellite
Satellites are launched into space on a rocket. Once there, they orbit (go around) the Earth collecting information with their advanced equipment. They beam the information back to supercomputers on Earth. Weather satellites take pictures of the Earth from above, helping scientists understand what the weather is doing and what might happen next.
Weather Station
A weather station is a place where there is lots of equipment, specially made to record made to record information about the weather. They record how hot or cold it is; how much rain falls; how fast the wind is moving and lots of other things. There are weather stations all over the world, including on some mountain tops. The information is sent to computers so people know what the weather is doing at each station. The information also helps people to understand the weather, and what it might do next.
Wind
Wind is air moving around. Some winds can move as fast as a racing car, over 100 miles an hour. Winds can travel around the world. Wind can make you feel cold because you lose heat from your body faster when it is windy. Weather forecasters need to know the speed and direction of the wind. The strength of wind is measured using the Beaufort scale from wind force 0 when there is no wind, to wind force 12 which can damage houses and buildings and is called hurricane force.
Winter
The winter months are December, January, February. Winter is when the days get shorter and the weather is cold. It sometimes snows in the winter.