National Centers for Environmental Prediction. Central computer and communications facility of the National Weather Service; located in Washington, DC.

A rainbow formed by light rays which have been reflected from an extended water surface. Not to be confused with a reflected rainbow whose image may be seen in a still body of water. The center of a reflection rainbow is at the same elevation as the sun b ...

Wind with a speed between 4 and 27 knots (4 and 31 mph); Beaufort scale numbers 2 through 6.

Abbreviation for precipitation-evaporation quotient.

An instrument for the measurement of the net flux of downward and upward total (solar and terrestrial) radiation through a horizontal surface.

The intensity (flux per unit solid angle) of visible radiation weighted to take into account the variable response of the human eye as a function of the wavelength of light. Usually expressed in candles.

A recording anemoclinometer.

A type of rain gauge shield consisting of freely hanging, evenly spaced slats arranged circularly around the gauge. The advantage of this shield is that the slats do not easily accumulate snow, permitting its use on unattended gauges. See rain gauge shiel ...

The maximum distance along the runway at which the runway lights are visible to a pilot at touchdown. Runway visual range may be determined by an observer located at the end of the runway, facing in the direction of landing, or by means of a transmissomet ...

The element directly responsive to the value of the measured variable.

An instrument which measures the transmissivity of the atmosphere between two points for the determination of visual range.

A defective maximum thermometer of the liquid-inglass type in which the mercury flows too freely through the constriction. Such a thermometer will indicate a maximum temperature that is too low.

An instrument for measuring the extinction coefficient in water.

Hygrometer in which the dew (frost) point is determined by observing the temperature of an artificially cooled surface at the moment at which dew (frost) first appears on it.

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

The maximum rate at which precipitation can pass through the surface into the soil, for a given soil in a given condition.

A high-altitude sounding system consisting of a small solid- propellant research rocket carried aloft by a large plastic balloon. The rocket is fired near the maximum altitude of the balloon flight.

A type of recording siphon barometer. The mechanically magnified motion of a float resting on the lower mercury surface is used to record atmospheric pressure on a rotating drum.

In nautical terminology, a contraction for "weather glass" (a mercury barometer).

Strong winds concentrated within a narrow band in the atmosphere. The jet stream often "steers" surface features such as front and low pressure systems.