Download Section 1: Elements of Weather What is weather? • Weather

Section 1: Elements of Weather
What is weather?
• Weather
• Different observations give you clues to the weather
• Weather is described by factors such as temperature, humidity, precipitation, air pressure,
wind, and visibility
What is temperature and how is it measure?
• Temperature
• Thermometer
• Thermometer uses a liquid such as alcohol or mercury
o Liquid is sealed in a glass tube
o When air gets warmer, the liquid expands and rises in the tube
o Cooler air causes the liquid to contract
• Electrical thermometer
o Temperature becomes higher, the electric current flow increases
What is humidity and how is it measured?
• Humidity
o As more water evaporates and becomes water vapor, the humidity of the air increases
• Relative humidity
• When air is saturated the rates of evaporation and condensation are the same
• Saturated air has a relative humidity of 100%
• Psychrometer
• Air can become saturated when evaporation adds water vapor
• Air can also become saturated when it cools to its dew point
• Dew point
o When air temperature drops below the dew point, condensation forms
o Can cause dew on surfaces cooler than the dew point
o Can also form fog and clouds
What is precipitation and how is it measured?
• Water vapor in the air condenses on tiny particles in the air to form clouds
• Precipitation
• Four main forms of precipitation are rain, snow, hail, and sleet
• Rain is the most common form of precipitation
o Droplets form by condensation and collide to form larger droplets
o When the become heavy enough they fall
o Rain is measured with a rain gauge
• Snow forms when air temperatures are so low that water vapor turns into a solid
• Ball or lumps of ice fall from clouds called hail
• Sleet forms when rain falls through a layer of freezing air