The mean difference between the readings of a given instrument and those of a standard instrument.

Liquid water at temperatures colder than freezing.

A hydrometeor consisting of an aggregate of microscopic and more-or-less hygroscopic water droplets suspended in the atmosphere. It reduces visibility to a lesser extent than fog. The relative humidity of mist is often less than 95 percent.

An aneroid barometer with a scale graduated in altitude instead of pressure units.

The meteorological visual range, which can be estimated from the average extinction coefficient using the Koschmieder equation.

A surface weather observation, made at periodic times, of sky cover, state of the sky, cloud height, atmospheric pressure reduced to sea level, temperature, dew point, wind speed and direction. amount of precipitation, hydrometeors and lithometeors. and s ...

An accumulation of granular ice tufts on the windward sides of exposed objects that is formed from supercooled fog or cloud and built out directly against the wind.

A clockwise change in wind direction. Veering winds with height are indicative of warm air advection (WAA).

An instrument for measuring radiant energy. It consists of an ether differential thermometer with blackened bulbs. One of the bulbs is exposed to the unknown radiation and the other to a black body source whose temperature can be varied. Equality of radia ...

Sir Napier Shaw's name for the approximate absolute temperature scale,

A system of designating meteorological observing stations by number. established and administered by the World Meteorological Organization. Under this scheme, specified areas of the word are divided into "blocks" each bearing a two-number designator. Stat ...

The measurement and computation of wind speeds and directions at various levels above the surface of the earth. Methods include pilot balloon observations, rabals, rawin or rawinsonde observations, radar tracking, or acoustic sounding.

A photometric unit of illuminance or illumination equal to one lumen per square meter

An instrument for measuring the frost point of the atmosphere.

A rainbow of angular radius of about 50

The limiting values of ceiling, visibility, and wind, or runway visual range, established as safety minimum for aircraft landings and take-offs.

Abbreviation for precipitation-evaporation quotient.

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.

As used by the U.S. Army Corps of Engineers, the departure (in

Wind with a speed between 22 and 27 knots (25 and 31 mph); Beaufort scale number 6.