What is weather?
 In brief, weather is the condition of the Earth's atmosphere at a given time and in regards to how it affects life and human activities. That condition is generally described in terms of precipitation (rain, snow, hail, etc.) visibility (cloudiness vs. clarity), hot or cold air, humidity, and wind (speed, direction and frequency). In order to accurately describe the weather, people have developed a number of instruments designed to measure these components.
Part of understanding weather involves understanding the atmosphere and its components. The atmosphere consists of several layers stretching from the Earth's surface to outer space.
The layer of atmosphere closest to the surface is the troposphere, where weather and most clouds occur. In the troposphere, the temperature generally decreases as altitude increases.
The tropopause separates the troposphere from the next layer. The tropopause is characterized by little or no change in temperature altitude increases.
This next layer is the stratosphere, characterized by a slight temperature increase with altitude and the absence of clouds.The stratosphere contains the ozone layer. Only the highest clouds (cirrus, cirrostratus, and cirrocumulus) are in the lower stratosphere.
Above the stratosphere and separated by the stratopause is the mesosphere, characterized by temperatures that quickly decrease as height increases. The mesosphere ends at the mesopause which separates it from the next layer.
Next is the ionosphere, a large layer that contains many ions and free electrons (plasma). Auroras occur in the ionosphere.
Above the ionosphere is the exosphere, the outermost layer of the Earth's atmosphere. The lower boundary of the exosphere is called the critical level of escape, where atmospheric pressure is very low (the gas atoms are very widely spaced) and the temperature is very low.
Composed of the exosphere and part of the ionosphere, the thermosphere is a thermal classification of the atmosphere. In the thermosphere, temperature increases with altitude.
What causes weather?
 Weather is the result of masses of air moving across the earth. These air masses are warmed when the sun shines on and heats the earth.
The sun always heats the earth more at the equator and less at the north and south poles. This uneven heating of the earth causes warm air masses to form at the equator and cold air masses to form at the poles. The warm air masses tend to move towards the poles, while the cold air masses tend to move toward the equator. When these air masses meet and move against each other, clouds and precipitation (rain or snow) result.
What makes up weather?
- Air Temperature: how hot or cold the air feels
- Air Pressure: the weight of the air on the earth
- Wind Speed/Direction: how fast the wind is blowing and from what direction (North, South, East, or West)
- Precipitation: how much rain/snow falls on the earth
- Relative Humidity: a relative measure of the humidity in the earth's air
- Clouds: the type and amount of clouds in the sky, and the types of precipitation produced by the clouds
- Visibility: how far we can see and what types of clouds and precipitation block our view
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