The distance that an observer can see vertically into a surface-based obscuring phenomenon such as fog, rain, or snow. The distance estimate must be based upon ceiling balloon ascensions or ceiling light projector measurements.

A curve showing the variation of temperature with height in the free air. See lapse rate.

See standard atmosphere.

The array of indicating marks and figure in relation to which the position of an index is observed, i.e. a scale plate on a recorder.

The depth of water that would result from the melting of snow or ice, assuming measurement on a horizontal surface and no infiltration or evaporation.

A conductor or system of conductors for radiating and/or receiving radio energy. Also called aerial.

An instrument for determining the direction from which radio waves approach a receiver. It may consist of a manually operated direction indicator, or it may use a servo system to position the antenna automatically in the direction of the incident waves.

Electromagnetic radiation of shorter wavelength than visible radiation but longer than x-rays, between 0.02 and 0.4 micron (200 and 4000 angstrom).

An instrument for determining the direction of cloud motion. There are two basic designs of nephoscope, the directvision nephoscope and the mirror nephoscope.

A refraction phenomenon similar to a parahelion, but occurring generally at a distance of 120

A special type of radar target, usually a comer reflector, tied beneath a free balloon and designed to be an efficient reflector of radio energy.

NEXt Generation RADar. A NWS network of about 140 Doppler radars operating nationwide.

A halo consisting of a faint white circle passing through the Sun and running parallel to the horizon for as much as 360

The upper surface of a column of liquid.

The gravity flow of water within soil.

Nested Grid Model generated every 12 hours by NCEP.

A contact anemometer connected to an electrical circuit which is so arranged that the average wind speed is indicated.

Solar radiation scattered by particles in the atmosphere.

The minimum temperature shown by a minimum thermometer exposed in an open situation with its bulb at the level of the tops of the grass blades of short turf.

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.