Formation of a single water drop by the union of two or more colliding drops.

An instrument used to measure the water vapor content of the air. A type of hygrometer. It consists of a wet-bulb and a dry-bulb thermometer. See aspiration psychrometer, Assmann psychrometer. hygrodeik, sling psychrometer.

Very small precipitation drops (diameters less than 0.5 mm) that appear to float with air currents while falling in an irregular path. Unlike fog droplets, drizzle falls to the ground.

A cover which fits over a large inflated balloon to facilitate handling in high or gusty winds.

A type of wind vane having a split or V-shaped tail. The apex orients itself to the direction of the wind.

The change in the measured transducer output caused by changes in ambient temperature. Usually expressed a percentage of full scale.

Same as wave pole.

The total electromagnetic radiation emitted by the sun. About 99.9 percent of its energy output falls within the wavelength interval from 0. 15 microns to 4.0 microns, with peak intensity near 0.47 microns. About one-half of the total energy in the solar ...

A synoptic code approved by the World Meteorological Organization in which the observable meteorological elements are encoded and transmitted in "words" of five numerical digits length. Often abbreviated synoptic code.

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

Same as altimeter setting.

The total of direct solar radiation and diffuse sky radiation received by a unit horizontal surface. Global radiation is measured by pyranometers.

See constant-level balloon.

Companion to the wet-bulb thermometer in a psychrometer. Used to measure ambient air temperature.

A definite portion of a stream channel, commonly taken between two gauging stations, but may be taken between any two specified points.

Tables prepared from the psychrometric formula and used to obtain vapor pressure, relative humidity, and dew point from values of wet-bulb and dry-bulb temperatures.

Precipitation composed of balls or irregular lumps of ice with diameters between 5 and 50 mm.

For a given cloud or cloud laver. the lowest level in the atmosphere at which the air contains a perceptible quantity of cloud particles.

Forecasting weather by the use of numerical models, run on high speed computers. Most of the NWP for the National Weather Service is done at the National Centers for Environmental Prediction (NCEP).

Same as atmometer.