Water Cycle(1)

The process by which water is transpired and evaporated from the land and water. condensed in the clouds. and precipitated out onto the earth once again to replenish the water in the bodies of water on the earth.

Water equivalent(6)

The depth of water that would result from the melting of a snow sample. Typically about 10 inches of snow will melt to 1 inch of water. producing a water equivalent of 10 to 1.

Water Vapor (H2(5)

Water vapor is the primary gas responsible for the greenhouse effect. It is believed that increases in temperature caused by anthropogenic emissions of greenhouse gases will increase the amount of water vapor in the atmosphere. resulting in additional warming (see 'positive feedback').


Describes the short-term (i.e.. hourly and daily) state of the atmosphere. Weather is not the same as climate.

Weighing bucket rain gage(6)

A device that is calibrated so that the weight of rainfall is recorded directly in terms of rainfall in millimeters or in inches.

Wet-bulb depression(6)

The difference in degrees between the air temperature (dry-bulb temperature) and the wet-bulb temperature.

Wet-bulb temperature(6)

The lowest temperature that can be obtained by evaporating water into the air.

White frost(6)

Ice crystals that form on surfaces instead of dew when the dew point is below freezing.

Wind chill equivalent temperature(6)

A theoretical air temperature at which the heat loss from exposed skin under calm conditions is equivalent to the heat loss at the actual air temperature and under the actual wind speeds.

Wind Chill Index(3)

A means of quantifying the threat of heat loss from the human body during windy and cold conditions.

Wind Chill(3)

The portion of the cooling of the human body caused by air motion. Wind chill becomes important for human health as air motion accelerates the rate of heat loss from a human body. especially when temperatures are below 45�F.

Wind shear(6)

A difference in wind speed or direction between two wind currents in the atmosphere.

Wind Vane(6)

An instrument used to determine wind direction.

Wind-chill factor(6)

The cooling effect of any combination of temperature and wind. expressed as the loss of body heat. Also called wind-chill index.


A large. conical. open bag designed to indicate wind direction and relative speed. usually used at small airports.

Winter solstice(6)

Approximately December 22 in the Northern Hemisphere when the sun is lowest in the sky and directly overhead at latitude 23.5�S. the Tropic of Capricorn.


See GMT or Greenwich Mean Time.
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Americans’ health, security and economic wellbeing are tied to climate and weather. Every day, we see communities grappling with environmental challenges due to unusual or extreme events related to climate and weather. In 2011, the United States experienced a record high number (14) of climate- and weather-related disasters where overall costs reached or exceeded $1 billion. Combined, these events claimed 670 lives, caused more than 6,000 injuries, and cost $55 billion in damages. Businesses, policy leaders, resource managers and citizens are increasingly asking for information to help them address such challenges.