Temperature and Moisture

Temperature

Celsius (Centigrade) - The dominant expression of temperature in meteorology work, with certain exceptions for Kelvin and Fahrenheit. 

Fahrenheit - In meteorology, Fahrenheit is typically used only for surface observations in the United States.

Dewpoint Temperature

The temperature at which water vapor, if cooled, would begin to condense. When it is below 0 C it is occasionally referred to as the frost point. 

Relative Humidity 

Roughly equivalent to the ratio of the mass or vapor pressure of water in the air to the air's capacity for water vapor. A value of 100% indicates saturation, and a value of above 100% indicates supersaturation. 

NOTE: Dewpoint temperature is notably more useful than relative humidity, especially when comparing geographically different areas. However, relative humidity is a great way to express local water vapor levels to the public.

Wind Chill

Wind Chill expressions attempt to combine the effects of low air temperature with the ability to remove the warm layer of air in contact with the human skin.

The United States uses the New Wind Chill (JAG/TI) Index (F).