Dihydrogen oxide, molecular formula H2O.

The temperature to which a sample of air must be cooled, while the mixing ratio and barometric pressure remain constant, in order to attain saturation by water vapor. When this temperature is below O

A particular pattern of snow sampler having an internal diameter of 1.485 inches so that each inch of water in the sample weighs one ounce.

An air-launched balloon designed to be released in the eye of a tropical cyclone, float within the eye at predetermined levels, and transmit radio signals for RDF positioning.

A thermometer consisting of a clock mechanism the speed of which is a function of temperature.

Meteorological information issued by a watch office concerning the occurrence or forecast of weather phenomena which may affect the safety of aircraft operations.

The older name for the Celsius temperature scale. Officially abandoned by international agreement in 1948, but still in common use.

See ceilometer.

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

Federal Aviation Administration.

Solar and terrestrial radiation directed downwards (towards the earth's surface); incoming radiation.

A basic equation in daytime visual range theory, relating the apparent luminance of a distant black object, the apparent luminance of the background sky above the horizon, and the extinction coefficient of the atmosphere, or the air layer near the ground. ...

An inert gas. An element found in the atmosphere to the extent of only 0.000114 percent by volume. Its molecular weight is 83.7.

Same as water year.

General term for any device that measures precipitation: principally a rain gauge or snow gauge.

The process in which incident radiation is retained by a substance. A further process always results from absorption.

Winds from the four cardinal points of the compass; that is, north, east, south, and west winds.

A device used on certain types of instruments to prevent unwanted radiation from affecting the measurement of a quantity. Also called solar radiation shield.

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

Based upon damage patterns, classifies twisters into six categories of wind speed (F0 thru F5), ranging from 40 to 318 mph estimated wind speed.