Basic Weather Variables

1
Basic Weather Variables

• Temperature
• Pressure
• Humidity
• Wind
• Clouds
• Precipitation
• Visibility

2
Definitions

• Atmosphere The thin envelope of gases and
  particles that surrounds the Earth.
• Weather The state of the atmosphere (in terms
  of the variables) at a given place and instant of
  time.
• Meteorology The study of the atmosphere and the
  processes that cause weather.

3
Temperature

• Measures average molecular motion.
• Measuring device thermometer.
• Scale/unit Fahrenheit (F) Celsius (C)
  Kelvin (K).

4
Pressure

• Measures force per unit area.
• Measuring device barometer (mercury aneroid).
• Scale/unit inches/millimeters of mercury
  (in/mm) atmospheres (atm) millibars (mb)
  hectopascals (hPa).

5
Humidity

• A measure of water vapor content.
• Measuring device hygrometer psychrometer.
• Scale/unit vapor pressure (mb) relative
  humidity () dew point temperature (C or F)

6
Wind

• A measure of air motion.
• Measuring device anemometer pitot tube.
• Speed units miles/hour (mph) knots (kt).
• Direction compass point or azimuth angle (N/0
  E/90 S/180 W/270).

7
Cloud Types

• Cumulus - puffy, vertical development.
• Stratus - flat, horizontal development.
• Cirrus - wispy, very high.
• Nimbus - precipitation producing.

8
Cloud Cover

• 0/10 clear (CLR).
• 1/10 - 5/10 scattered (SCT).
• 6/10 - 9/10 broken (BKN).
• 10/10 overcast (OVC).