Wind with a speed below 1 knot (1 mph); Beaufort scale number 0.

Abbreviation for visual flight rules, but commonly used to refer to the relatively favorable weather and/or flight conditions to which these rules apply.

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.

An instrument for studying, or examining substances in, polarized light. See Savant polariscope.

A device used by oceanographers to obtain subsurface samples of sea water. The "bottle" is lowered by wire, its valves open at both ends. It is then closed in situ by allowing a weight (called a messenger) to slide down the wire and strike the reversing m ...

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

A system of physical units based upon the use of the meter, the metric ton (106 grams), and the second as elementary quantities of length, mass, and time, respectively.

Same as wind sock.

National Weather Service. Administered by the U.S. Department of Commerce.

A type of anemometer in which the rotation of an element serves to measure the wind. Rotation anemometers are divided into two classes; those in which the axis of rotation is horizontal, such as the windmill anemometer, and those in which the axis of rota ...

Particle on which the freezing of water occurs.

A mercury barometer in which the lower mercury surface is larger in area than the upper surface. The basic construction of a cistern barometer is as follows: A glass tube one meter in length, sealed at one end is filled with mercury, and then inverted. Th ...

The distance or length of flow of the air past a point during a given interval of time.

A reversing thermometer (for seawater temperature) which is not protected against hydrostatic pressure. The mercury bulb is therefore squeezed, and the amount of mercury broken off on reversal is a function of both temperature and of hydrostatic pressure.

A small, limited-capacity central processing unit contained entirely on one semiconductor chip.

The range through which the input may be varied without initiating a response. Usually expressed as a percentage of full-scale range.

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

A system of physical units based on the use of the centimeter, gram. and the second as elementary quantities of length. mass. and time.

A graphical representation of stage or discharge at a point on a stream as a function of time.

Pertaining to measurements or devices in which the output varies continuously, i.e. voltage or rotation signals. Compare to digital.