That stage, on a fixed river gauge, at which overflow of the natural banks of the stream begins to cause damage in any portion of the reach for which the gauge is used as an index.

An inert gas. A colorless, monatomic element which is found to occur in dry air to the extent of only 0.000524 percent by volume. Helium is very light, having a molecular weight of only 4.003 and specific gravity referred to air of 0.138. Because helium i ...

Any one of six gases, helium, neon, argon, krypton, xenon, and radon, all of whose shells of planetary electrons contain stable numbers of electrons such that the atoms are chemically inactive.

A system of physical units based upon the use of the meter, the metric ton (106 grams), and the second as elementary quantities of length, mass, and time, respectively.

A radiosonde which is dropped by parachute from an aircraft for the purpose of obtaining soundings of the atmosphere below.

An instrument of the aspiration condenser type which measures the concentration and mobility of small ions.

A type of atmometer. It is a pan used in the measurement of the evaporation of water into the atmosphere. The NWS Class A pan is a cylindrical container 48 inches in diameter and 10 inches deep.

The visibility along an identified runway, determined from a specified point on the runway with the observer facing in the same direction as a pilot using the runway. Compare to runway visible range.

Routine broadcast of meteorological information for aircraft in flight.

The atmospheric pressure at the level of the barometer. May or may not be the same as station pressure.

The process by which water in plants is transferred as water vapor to the atmosphere. Also, the amount of water so transferred.

Cathode Ray Tube. A display element, consisting of a vacuum tube and screen, used with computers.

Same as atmometer.

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

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.

Temperature assumed by an unsaturated air parcel when brought adiabatically to a standard pressure (1,000 mb).

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

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.

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

in folklore, a name for fire.