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Weather Facts

Window on a rainy day.What is weather?

The dictionary defines weather as the state of the atmosphere at a particular time and place with respect to temperature, moisture, calm or storm, and the amount of cloud cover. It's hard to talk about weather because it involves more than rain, snow, clouds or the sun. It involves things we can't see like air pressure, wind, solar radiation and humidity. These elements are organized into various weather systems, such as monsoons, areas of high and low pressure, thunderstorms, and tornadoes.

Why should we study the weather?

Weather affects nearly everything we do. It especially impacts people who work or play outdoors. If you are a pilot, a construction worker, a fisherman, a farmer or even going on a vacation, you will want someone else to be able to tell you how the weather will affect you.

What about the atmosphere?

Sunset over the mountainsThe blanket of air around the earth is called the atmosphere. It is about 15 miles thick. All of our weather happens in the bottom layer of the atmosphere, called the troposphere, which is six to ten miles thick. Meteorology is the study of the changes in temperature, air pressure, moisture, and wind direction in the troposphere.

In the darkest regions of deep space, the temperature is a chilly -450° Fahrenheit. Closer to our Sun, temperatures reach thousands of degrees Fahrenheit! What makes Earth's climate so moderate? Separating Earth from the extreme and inhospitable climate of space is a 500-mile-thick cocoon of gases called… you guessed it: the atmosphere!

There's more to know about in the atmosphere, and the layers of the atmosphere.

What about water and clouds?

A cloud occurs when the invisible water vapor in the air becomes visible water droplets or ice crystals. Water vapor becomes visible by cooling. That is what happens on a cold, wintry afternoon when you see your breath. Warm air leaving your mouth cools and forms visible droplets.

Rain cloudThere are many kinds of clouds, and each one signals a different kind of weather. Cumulus are puffy mid-level white clouds made of water and ice, usually associated with fair weather. Cirrus clouds are high up in the troposphere and are wispy and thin due to the strong winds at that altitude. Though they are composed of ice, they are usually associated with pleasant weather.

Stratus clouds , which form in lower parts of the troposphere, consist of water droplets and cover most of the sky with an even, gray color similar to a fog, which can signal light rain. Cumulonimbus clouds are tall, dense clouds shaped like a block or anvil. They signal thunderstorms as well as violent weather effects such as hail and lightning.

Photos of types of clouds

So what does all this mean?

All of our weather is created from two basic things: the sun and the moisture in the air. These two combine together to form Clouds, to make rain and thunderstorms, and to cause winds to blow. The sun emits energy at an almost constant rate, but a region receives more heat when the sun is higher in the sky and when there are more hours of sunlight in a day. The high sun of the Tropics makes this area much warmer than the poles, and in summer the high sun and long days make the region much warmer than in winter.

Blown umbrellaThe wind blows because air has weight. Cold air weighs more than warm air, so the pressure of cold air is greater. When the sun warms the air, the air expands, gets lighter, and rises. Cooler, heavier air blows to where the warmer and lighter air was, or in other words, wind usually blows from areas of high air pressure to areas of low pressure. If the high pressure area is very close to the low pressure area, or if the pressure difference (or temperature difference) is very great, the wind can blow very fast.

The sun is the engine that drives the motion of water in our atmosphere. This movement of water is called the water cycle, which is also known as the hydrologic cycle. It involves the continuous circulation of water in the atmosphere through a cycle of:

Study this diagram to help you understand the Hydrologic Cycle.

What about thunder and lightning?


When cold air meets warm air, the cold air sinks under the warm air, forcing it to rise quickly. The rising air takes water vapor with it, which cools and condenses, forming cumulonimbus clouds, sometimes called thunderheads. No one is sure exactly why lightning occurs, but water droplets and ice particles bang together in the cloud, helping to build up positive and negative electrical charges. Electricity flows between the charges, which results in a flash of electricity known as lightning, which heats the air around it. The heat causes the air to expand with an explosive force, resulting in a loud sonic boom we call thunder.

The air in the core of a lightning bolt has been estimated to be heated to as much as 54,000 degrees Fahrenheit. That happens to be about six times hotter than the surface of the sun!

Become an expert about thunder and lightning!

Lightning from the Exploratorium
Ingredients for a Thunderstorm
Lifecycle of a thunderstorm
Types of Thunderstorms


8 inch hailstone
NOAA image of record-setting hailstone

On June 22, 2003, a hailstone recovered in Aurora, Nebraska, had a diameter of 7" (17.8 cm) and a circumference of 18 3/4" (47.6 cm). This hailstone was larger than the previous record large hailstone that fell in Coffeyville, Kansas, in 1970 (5.7" (14.5 cm) diameter and 17.5" (44.5 cm) circumference). However, weight, is the most important measurement. An accurate weight could not be determined for the Aurora hailstone; so the Coffeyville hailstone of 1970 remains the heaviest hailstone weighed and verified in the United States at 1.67 pounds (0.76 kg).

Hail causes $1 billion in damages to crops and property each year. Hailstones can fall at speeds up to 120 mph (53 m/s).

The costliest United States hailstorm: Fort worth, Texas, May 5 1995. Total damage was $2 billion.

Guess what? Nature has its own forecasters!

Groundhog looks at the sun.People have been forecasting the weather for centuries. They once looked to plants and animals for hints about the weather. Before it rains, ants move to higher ground, cows lie down, pine cones open up, frogs croak more frequently, and sheep's wool uncurls. Before technology, folks also made forecasts by studying the clouds.

You may have been raised to believe that groundhogs can predict the length and severity of winter weather. Groundhog Day, which is celebrated on February 2 in the United States, is based on ancient Celtic beliefs that if winter's midpoint was sunny and clear, winter would be long and cold. Nowadays, in the U.S., a groundhog named Punxsutawney Phil is the keystone of the celebration. If he sees his shadow, it is thought that this presages a long winter. (Unfortunately, Phil's "predictions" have been accurate only about one-third of the time.)

So with all these factors, how can we predict/forecast the weather?

A daily weather forecast involves the work of thousands of observers and meteorologists all over the world, and the work of thousands of machines. Modern computers make forecasts more accurate than ever, and weather satellites orbiting the earth take photographs of clouds from space. Weather forecasts made for 12 and 24 hours are typically quite accurate. Forecasts made for two and three days are usually good. Beyond about five days, forecast accuracy falls off rapidly.

thermometerdeviceObserving Weather

What about weather in Idaho?

SkierThe National Oceanic and Atmospheric Administration (NOAA) watches the weather over the entire world. You can follow these links to find out more about Idaho's weather. The National Weather Service has several offices in Idaho because we are such a big state. The Boise office monitors weather and weather conditions in Southwest Idaho. Take time to visit other places and their weather around Idaho at this NOAA site, or view the weather from these Idaho traffic cameras.

Pocatello weather from NOAA weather pages has lots of links to local weather information in Idaho, satellite and radar pictures of the Northwest as well as weather watches and warnings.

The record low temperature in Boise is -17° Fahrenheit, but the record high is 111° Fahrenheit. Tornados are pretty unusual in Idaho, but a few small ones are recorded every year.

Amazing Weather Facts

  • One inch of rain over one square mile equals to 17.4 million gallons (66 million liters) of water.
  • The weight of one inch of water over one square mile equals over 145 million pounds (66 million kg).
  • 145 million pounds of water is almost 73,000 tons or the weight of 241 locomotives. This is a lot of water held up by wind.
  • partly cloudyClouds are made of trillions of tiny droplets of water (or when cold enough, ice crystals)!
  • There is so much water in the air that if it all fell as rain at the same time, it could fill enough buckets to reach from the earth to the sun 57 million times!
  • You can tell the temperature by counting the clicks a cricket makes in 15 seconds and adding 37!

Head outside, study the weather and become a meteorologist! There is always some interesting weather to observe.

Convert Fahrenheit and Celsius

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