An instrument which measures the scattering function of particles suspended in a medium in order to determine the visual range through the medium. See visibility meter.

See ceilometer.

The mass density of a parcel of air expressed in units of mass per volume.

The temperature at which all three phases of a substance can exist in equilibrium. This temperature occurs at only one pressure. The triple-point of water is 273.16 K and is the basis of the Kelvin scale.

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.

Abbreviation for mean sea level.

Same as mercury barometer.

Automated Local Evaluation in Real Time. Network of automatic rain gauges that transmit via VHF radio link when precipitation occurs. Some sites are also equipped with other sensors such as temperature, wind, pressure, river stage or tide level. More info ...

The scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surface. In terms of the hydrologic cycle, the ...

A method of streamflow routing which assumes that storage is a linear function of the weighted flow in the reach and is adaptable to a simple mathematical solution.

Generally, the relative states of inflow, outflow, and storage of moisture over a given area of earth's surface.

That portion of the record of a microbarograph between any two (or a specified small number) of successive crossings of the average pressure level (in the same direction). Analogous to microseism.

Same as aneroid barometer. Holostelic means wholly made of solids, while aneroid means devoid of liquid.

An evaluation, according to set procedures, of those weather elements which are most important for aircraft operations. Always includes cloud height or vertical visibility, sky cover, visibility, obstructions to vision, certain atmospheric phenomena, and ...

The depth below which the ground is saturated with water. No water table exists if the ground water is confined by an overlying impermeable stratum, as in the case of artesian ground water.

The state of the weather with respect to its effect upon the kindling and spreading of forest fires.

A liquid-in-glass or liquid-in-metal thermometer using mercury as the liquid.

Turbulence encountered by aircraft when flying through air space devoid of clouds. Thermals and wind shear are the main causes.

A wind blowing in a direction perpendicular to the course of a moving object.

A mercury barometer which measures atmospheric pressure by weighing the mercury in the column or cistern.