Same as wind sock.

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

An atmometer consisting of a porous porcelain or ceramic container connected to a calibrated reservoir filled with distilled water. Evaporation is determined by the depletion of water in the reservoir.

General term for an instrument used to make direct measurements of visual range or measurements of the physical characteristics of the atmosphere which determine the visible range.

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

The standard deviation of a sufficiently large number of measurements of the same quantity by the same instrument or method. The non-correctable part of the inaccuracy of an instrument, it represents the limit of measurement precision. The uncertainty of ...

Any one of numerous devices for the measurement of either speed alone or of both direction and speed (set and drift) in flowing water.

See calorie.

The decrease of an atmospheric variable with height, the variable being temperature, unless otherwise specified.

An instrument used to indicate wind direction.

A combination cup anemometer and pressure-plate anemometer, consisting of an array of cups about a vertical axis of rotation, the free rotation of which is restricted by a suitable spring arrangement.

Any quantity, such as force velocity, or acceleration, which has both magnitude and direction at each point in space, as opposed to scalar which has magnitude only. Such a quantity may be represented geometrically by an arrow of length proportional to its ...

A clock-driven instrument mounting which automatically and continuously points in the direction of the sun. It is used with a pyrheliometera,hen continuous direct solar radiation measurements are required.

One of the radiation laws which states that the wavelength of maximum radiation intensity for a black body is inversely proportional to the absolute temperature of the radiating black body.

A decrease in the central pressure of a pressure system. Usually applied to a low rather than to a high.

The height of the cloud base above the local terrain.

in United States weather observing practice, the highest "instantaneous" wind speed recorded at a station during a specified period, usually the 24-hour observation day. Therefore, a peak gust need not be a true gust of wind.

A thermograph in which ventilation is provided by a suction fan.

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 ...

A graphical aid used in fire weather forecasting to calculate the degree of forest-fire danger (or burning index). Commonly in the form of a circular slide rule, the firedanger meter relates numerical indices of (a) the seasonal stage of foliage, (b) the ...