Instrument for measuring the depth of water from precipitation that is assumed to be distributed over a horizontal, impervious surface and not subject to evaporation.

A set of regulations set down by the U.S. Civil Aeronautics Board to govern the operational control of aircraft on instrument flight. The abbreviation of this term is seldom used to denote the rules themselves, but is in popular use to describe the weathe ...

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

The difference between the input quantity applied to a measuring instrument and the output quantity indicated by the instrument. The inaccuracy of an instrument is equal to the sum of its instrument error and its uncertainty.

A rainbow seen in the spray of the ocean. It is optically the same phenomenon as the ordinary rainbow.

The difference between the air temperature and the dew-point. Also called dew-point deficit, dew-point depression.

A balloon used to carry a radiosonde aloft, considerably larger than pilot balloons or ceiling balloons.

A calorimetric radiation instrument of historic interest used for the measurement of outgoing heat radiation from the earth during an interval of time. The time integration is performed by allowing the radiation to fall on an uninsulated vessel containing ...

Precipitation composed of liquid water drops more than 0.5 mm in diameter, failing in relatively straight, but not necessarily vertical, paths. Compare to drizzle.

The temperature at which an object gives out as much radiation as it receives from its surroundings.

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).

The component of the radiosonde which includes the modulating blocking oscillator and the radiofrequency carrier oscillator.

A wind scale adapted by the U.S. Forest Service for use in the forested areas of the northern Rocky Mountains (NRM). It is an adaptation of the Beaufort wind scale. The difference between these two scales lies in the specification of the visual effects of ...

An instrument which automatically records the voltage applied to it, as a function of time.

See ceilometer.

A device that combines several separate communications signals into one and outputs them on a single line.

The temperature registered by a thermometer with its bulb at the level of the tops of the grass blades in short turf.

A hydrometeor consisting of a visible aggregate of minute water droplets suspended in the atmosphere near the earth's surface. Fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface.

Same as fogbow.

The direction, with respect to true north, from which the wind is blowing. Distinguish from magnetic wind direction. In all standard upper-air and surface weather observations, it is true wind direction that is reported.