A thermometer which utilizes the thermal properties of gas. There are two forms of this instrument: (a) a type in which the gas is kept at constant volume, and pressure is the thermometric property, and (b) a type in which the gas is kept at constant pres ...

As used by the U.S. Army Corps of Engineers, the departure (in

For a given location, a measure of the long-range effectiveness of precipitation in promoting plant growth. Also called precipitation-evaporation index.

A general term to designate apparatus designed to observe the details of weather during thunderstorms.

A wooden enclosure about sixteen feet square and eight feet high with a precipitation gauge at its center. The function of the fence is to minimize eddies around the gauge and thus insure a catch that is representative of the actual rainfall or snowfall.

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

Wind with a speed between 7 and 10 knots (8 and 12 mph), Beaufort scale number 3.

See radiosonde commutator.

A photometric unit of illuminance or illumination equal to one lumen per square centimeter.

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.

The programs and instructions which direct a computer.

Thermometer used for measuring the lowest temperature attained during a given interval of time, for example, a day.

The addition of one or more redundant bits to information to verify its accuracy.

A fabric cone attached to a metal ring and used to indicate wind direction. often at airfields.

The ceiling classification which is applied when the ceiling height is determined by timing the ascent and disappearance of a ceiling balloon or pilot balloon.

The part of a measuring instrument which responds directly to changes in the environment.

See feed.

An instrument which measures the rate of evapotranspiration. It consists of a vegetation soil tank so designed that all water added to the tank and all water left after evapotranspiration can be measured.

In aviation terminology, route or terminal weather conditions of sufficiently low visibility to require the operation of aircraft under instrument flight rules.

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).