Glossary of Meteorological Terms (W)

W

Wadi gauge

Same as river gauge or stream gauge.

Warning stage

The stage on a fixed river gauge at which it is necessary to begin issuing warnings or river forecasts if adequate precautionary measures are to be taken before flood stage is reached.

Water

Dihydrogen oxide, molecular formula H2O.

Water balance

Balance of the water resources of a region, comparing precipitation and inflow with outflow, evaporation, and accumulation.

Water budget

See hydrologic accounting.

Water equivalent

The depth of water that would result from the melting of snow or ice, assuming measurement on a horizontal surface and no infiltration or evaporation.

Water-flow pyrheliometer

An absolute pyrheliometer, developed by C.G. Abbott, in which the radiation-sensing element is a blackened water-calorimeter.

Water-stage recorder

A device for obtaining a continuous record of stage at a point on a stream. The most common recorders consist of a float-actuated pen which traces a record on a clock driven chart.

Water table

The depth below which the ground is saturated with water. No water table exists if the ground water is confined by an overlying impermeable stratum, as in the case of artesian ground water.

Water year

Any twelve-month period, usually selected to begin and end during a relative dry season. Used a basis for processing streamflow and other hydrologic data. The period from October 1 to September 30 is widely used in the U.S.

Watershed

The total area drained by a river and its tributaries. Same as river basin.

Watt

A unit of power equal to one joule per second or 10⁷ ergs per second.

Wave pole

A device for measuring sea-surface waves. It consists of a weighted pole below which a disk is suspended at a depth sufficiently deep for the wave motion associated with deep-water waves to be negligible. The pole will then remain nearly as if anchored to the bottom, and wave height and period can be acertained by observing or recording the length of the pole that extends above the surface.

Wave recorder

An instrument for recording ocean waves. Most recorders are designed for recording wind waves, that is waves of periods up to about 25 seconds, but some are designed to record waves of longer periods such as tsunamis or tides.

Wave staff

Same as wave pole.

Weather

The state of the atmosphere, mainly with respect to its effects upon life and human activities. As distinguished from climate, weather consists of the short-term (minutes to months) variations of the atmosphere.

Weather glass

An old nautical term for mercury barometer.

Weather stick

Made of balsam fir or birch and attributed to northeast Native American tribes, the stick is said to rise indicating fair weather and to drop when inclement weather is approaching. The movement of the tip appears to track the relative humidity.

Weighing rain gauge

A precipitation gauge consisting of a receiver in the shape of a funnel which empties into a bucket mounted upon a weighing mechanism. The weight of the catch is recorded as inches of precipitation.

Weight barograph

A recording weight barometer.

Weight barometer

A mercury barometer which measures atmospheric pressure by weighing the mercury in the column or cistern.

Wet Bulb Globe Temperature (WBGT)

A measure of the heat stress in direct sunlight calculated from air temperature, humidity, wind, and solar radiation (radiant heat). It differs from the heat index which takes into consideration temperature and humidity and is calculated for shady areas.

Wet-bulb depression

Difference between the temperatures of the dry-bulb and the wet-bulb thermometers of a psychrometer.

Wet-bulb temperature

The lowest temperature that can be obtained on a wet-bulb thermometer in any given sample of air. Obtained by evaporation of water (or ice) from the muslin wick. Used in computing dew point and relative humidity.

Wet-bulb thermometer

A thermometer with a muslin-covered bulb which is moistened. Used to measure wet-bulb temperature.

Wet-bulb zero height (WBZ)

The height above ground level (in feet) where the wet-bulb temperature goes below 0°F.

White body

A hypothetical "body" whose surface absorbs no electromagnetic radiation of any wavelength. An idealization exactly opposite to that of the black body. In nature, no true white bodies are known. Most white pigments exhibiting high reflectivity for visible radiation are fairly good absorbers in the infrared range, hence they are not white bodies in the sense of radiation theory. However, one does speak of a white body with respect to a particular wavelength interval. Compare to black body, gray body.

White rainbow

Same as fogbow.

Whole gale

Wind with a speed between 48 and 55 knots (55 and 63 mph); Beaufort scale number 10.

Wien's law

One of the radiation laws which states that the wavelength of maximum radiation intensity for a black body is inversely proportional to the absolute temperature of the radiating black body.

Wild fence

A wooden enclosure about sixteen feet square and eight feet high with a precipitation gauge at its center. The function of the fence is to minimize eddies around the gauge and thus ensure a catch that is representative of the actual rainfall or snowfall.

Wilting point

Value of soil moisture, expressed as a percentage of the mass of dry soil, below which a plant living in the soil dies by wilting.

Wind

Air in motion relative to the surface of the earth. Almost exclusively used to denote the horizontal component.

Wind cone

Same as wind sock.

Wind direction

The direction from which the wind is blowing, measured in points of the compass or in azimuth degrees.

Wind gust

See gust and peak gust.

Wind passage

The distance or length of flow of the air past a point during a given interval of time.

Wind profiler

A radar that is used to measure vertical profiles of the wind. Also called wind profiler radar, wind profiling radar.

Wind rose

A flower-like diagram indicating the relative frequencies of different wind directions for a given station and period of time.

Wind run

The distance or length of flow of the air past a point during a given interval of time.

Wind shear

A local variation of the wind vector or any of its components in a given direction.

Wind sleeve

Same as windsock.

Wind sock

A fabric cone attached to a metal ring and used to indicate wind direction, often at airfields.

Wind speed

Rate of wind movement in distance per unit time.

Wind vane

An instrument used to indicate wind direction.

Wind vector

A component of the wind (often using Cartesian coordinates, i.e. X and Y wind vectors). Also, an arrow representing wind velocity, drawn to point in the direction of the wind and with a length proportional to wind speed. See also vector methods of wind measurement.

Wind velocity

A vector term which includes both wind speed and wind direction.

Wind wave

A wave resulting from the action of wind on a water surface.

Windmill anemometer

A rotation anemometer in which the axis of rotation is horizontal. The instrument has either flat vanes (as in the air meter) or helicoidal vanes (as in the propeller anemometer). The relation between wind speed and angular rotation is almost linear.

Winds aloft

The wind speed and direction at various levels in the atmosphere above the level reached by surface weather observations.

Winds-aloft observation

The measurement and computation of wind speeds and directions at various levels above the surface of the earth. Methods include pilot balloon observations, rabals, rawin or rawinsonde observations, radar tracking, or acoustic sounding.

Winds-aloft plotting board

A graphical aid used in the reduction of data from a winds aloft observation.

Windward

Situated on the side from which the wind blows.

Winter Storm Severity Index (WSSI)

A tool from the National Weather Service that forecasts the potential impacts of winter storms throughout the continental United States.

Wire weight gauge

A river gauge in which a weight suspended on a wire is lowered to the water surface from a bridge or other overhead structure to measure the distance from a point of known elevation to the water surface.

Wiresonde

An atmospheric sounding instrument which is supported by a captive balloon and used to obtain temperature and humidity data from the ground level to a height of a few thousand feet. The data is telemetered to the ground through a wire cable.

Word

A fixed-length group of bits representing the largest data element handled as a unit by a computer. Word length is determined by the capacity of the CPU registers.

Wyoming shield

A type of rain gauge shield consisting of two snow fences, developed by the University of Wyoming Water Resources Research Institute. See rain gauge shield.