A point (or line) on a scale used for reference or comparison purposes. In calibration of meteorological thermometers, for example, the fiducial points are 100

A halo consisting of a faint white circle passing through the Sun and running parallel to the horizon for as much as 360

The ratio of the existing amount of water vapor in the air at a given temperature to the maximum amount that could exist at that temperature. Usually expressed in percent.

A coating of ice, generally clear and smooth. formed by the freezing of supercooled water on a surface.

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

A cup anemometer with its shaft mechanically coupled to a magneto.

Integrated Flood Observing and Warning System. National Weather Service flood warning program.

Same as marine rainbow.

A type of photoelectric photometer used to measure high-altitude winds on the assumption that stellar scintillation is caused by atmospheric inhomogeneities being carried along by wind near the tropopause level.

A halo phenomenon consisting of a horizontal circle passing through the moon, corresponding to the parhelic circle through the sun. Produced by reflection of moonlight from ice crystals.

The difference between temperature measurements taken at two significant levels above the ground. Temperatures at 10 and 40 meters are commonly used.

That part of snow melt that reaches stream channels as runoff.

The total of all deviations of a transducer's output from a specified straight line in a constant environment.

In nautical terminology, a contraction for "weather glass" (a mercury barometer).

A type of pressure-plate anemometer in which the plate, restrained by a stiff spring, is held perpendicular to the wind. The wind-activated motion of the plate is measured electrically. The natural frequency of this system can be made high enough so that ...

A common unit used in measurement of atmospheric pressure. Defined as that pressure exerted by a one-inch column of mercury at standard gravity and a temperature of 0'C.

An instrument which measures the scattering function of particles suspended in a medium in order to determine the visual range through the medium. See visibility meter.

An instrument used for the determination of the electrical conductivity of the atmosphere.

Dihydrogen oxide, molecular formula H2O.

An absolute temperature scale with the degree of the Fahrenheit scale and the zero point of the Kelvin scale. The freezing point of water equals 491.69