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

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

A measure of long-term precipitation effectiveness. The ratio of the normal annual rainfall to the normal annual evaporation.

That horizontal wind velocity at which the Coriolis acceleration exactly balances the horizontal pressure force. It is directed along contour lines or isobars.

A device used by oceanographers to obtain subsurface samples of sea water. The "bottle" is lowered by wire, its valves open at both ends. It is then closed in situ by allowing a weight (called a messenger) to slide down the wire and strike the reversing m ...

A sudden, significant increase in station pressure.

Thermodynamic change of state of a system in which there is transfer of heat across the boundaries of the system. Compare to adiabatic process.

United Kingdom forecast model. (Available via AccuWeather.com Professional.)

The most common of the principal rainbow phenomena, which appears as an arc of about 42

See hurricane beacon.

The physical exposure of an instrument. The effect of immediate environment upon the representativeness of the measurements obtained by meteorological instruments is considerable and not always correctable. The purpose of the instrument shelter is to prov ...

An instrument for measuring differences of electric potential.

Rain gauge which registers precipitation that is too light to be registered by ordinary recording of the depth of water from precipitation. Same as ombrometer.

A continuous-recording barometer.

The succession of stages through which water passes on the ground and in the atmosphere: evaporation from land or bodies of water, condensation to form clouds, precipitation, accumulation in the soil or in bodies of water, and re-evaporation.

An aneroid barometer with a scale graduated in altitude instead of pressure units.

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.

A type of pressure-tube anemometer, named after the inventor.

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

A thermodynamic change of state in a system in which there is no transfer of heat or mass across the boundaries of the system. In an adiabatic process, compression always results in warming, expansion in cooling. Compare to diabatic process.