Air pressure is the weight of the molecules in a large mass of air. When molecules of air are cool, they are closer together than when they are warm. Cool air masses have high pressure, or more weight. Warm air masses have low pressure, or less weight.
Warm air also puts less pressure on the Earth than cool air. As a result, air in a low-pressure system rises. Cool air puts greater pressure on the Earth than warmer air. As a result, air in a higher pressure system sinks.

In the Northern Hemisphere, Earth's rotation causes winds to blow counterclockwise around a low-pressure system and converge. Around a high pressure system, the winds blow clockwise and diverge.

In a High Pressure System, cool, dense air sinks and clouds cannot form. High pressure systems often bring clear skies and fair weather. In a lower pressure system, warm less dense air rises. This rising air cools as water vapor in the air condenses. Therefore, a low-pressure system is often associated with cloudy weather and precipitation.
Use the text to above to help you complete the table
Low Pressure System | High Pressure System | |
|---|---|---|
cool, dense air sinks and clouds cannot form | ||
rising air cools as water vapor in the air condenses | ||
cloudy weather and precipitation | ||
clear skies and fair weather |

A) Create a diagram of the cold fronts before, while, and after passing.
B) Create a diagram of the warm fronts before, while, and after passing.

What type of front passed through St. Louis?
Explain the type of weather they experienced as the front passed.
What type of front passed through San Francisco? Explain the type of weather they experienced before and after the passing of the front.
A) Look it up! What does a negative number on the Celsius scale represent?
B) The weather station in Miami reported their temperature reading as - 3 degrees C. Argue weather you think this temperature was reported in error.
Which of these cities is experiencing clear dry weather conditions?
Which of these cities are probably experiencing stormy conditions or rainy weather conditions?