A decrease in the central pressure of a pressure system. Usually applied to a low rather than to a high.

The average temperature of the air as indicated by a properly exposed thermometer for a given time period, usually a day, a month, or a year.

A thermograph in which ventilation is provided by a suction fan.

Anemometer whicb measures wind speed by measuring the degree of cooling of a metal wire heated by an electric current. A type of cooling power anemometer.

A navigational aid used to facilitate the landing of an aircraft at an airport in instrument weather, i.e. low visibility.

A device for measuring the river stage. Also called stream gauge.

Any and all forms of water particles, liquid or solid, that fall from the atmosphere and reach the ground.

A device used to hold liquid-in-glass maximum and minimum thermometers in the proper recording position inside an instrument shelter, and to permit them to be read and reset. See Townsend support.

A high-altitude sounding system consisting of a small solid- propellant research rocket carried aloft by a large plastic balloon. The rocket is fired near the maximum altitude of the balloon flight.

A constant which describes the performance of a wind vane in response to a step change in wind direction. It is calculated from the relative amount of overshoot on two successive swings (half cycles) of a decaying oscillation. This specification is dimens ...

Same as windsock.

Thermometer in which the difference in the rates of expansion with temperature of a liquid and its receptacle is used as a measure of the temperature. The liquid used may be ethyl alcohol, toluene, petroleum, or mercury.

A conically shaped, copper rain gauge shield.

The point (physical and/or electrical) where two distinct data processing elements meet.

A chronograph used to make a time-record of certain measured meteorological elements. The most common type, the triple register, records wind direction and speed, duration of sunshine, and amount of rainfall (sensed respectively by a contact anemometer, M ...

Same as wind sock.

A self-recording psychrometer.

A hygrometer based upon the diffusion of water vapor through a porous membrane.

A hygrometer in which the rotation of the hygrometric element is a function of humidity.

The amount of sky covered or concealed by clouds or obscuring phenomena. It is reported in tenths, so that 0.0 indicates a clear sky and 1.0 (or 10/10) indicates a completely covered sky. The following classifications are used in aviation weather observat ...