What is Weather?

• Weather=the condition of the atmosphere at a certain time and place

• Words that describe weather:

• Temperature, humidity, precipitation, air pressure, wind, visibility

Temperature

• Temperature= how hot or cold something is

• Measured with a thermometer

• Thermometers- filled with liquid that expands or contracts depending on how warm the air is

Humidity

• Humidity= how much water vapor is in the air

• In 100% saturated air the condensation rate= evaporation rate

• Relative humidity- how much water vapor is there compared to how much is needed to reach saturation (50% humidity, 75% humidity)

Humidity

• Psychrometer- measures humidity

• How does air get saturated?

  • Evaporation adds water vapor to the air OR

  • Air can cool to below the dew point

• Dew point- temperature where more condensation happens than evaporation (water vapor becomes liquid dew)

Precipitation

• Precipitation= any form of water that falls to Earth from clouds

• 4 kinds: rain, snow, hail, sleet

• Rain= condensation droplets combine, get heavier, and fall

• Snow=air temperatures are low and water vapor becomes a solid

• Hail= balls of ice falling during a thunderstorm

• Sleet= rain falls through freezing air and forms ice

Air Pressure

• Air pressure-force of air molecules pushing on an area

• Presses in all directions so we don't feel it

• Measured with a barometer

Wind

• Wind=air moving parallel to the ground

• Caused by uneven heating of the Earth and pressure differences from one place to another

• Wind's speed is measured with an anemometer

• Wind direction is measured with a wind vane or a windsock.

Visibility

• Visibility= how transparent is the air

• Fog and air pollution can reduce visibility

• Poor visibility creates dangerous conditions for driving, biking, etc.

Tools for Measuring Weather

• Ground station

• Weather buoy

• Ship

• Satellite

• Airplane