Small particle on which water vapor condenses.

A feeble oscillatory disturbance of the earth's crust, detectable only by very sensitive seismographs. Certain types of microseisms seem to be closely correlated with pressure disturbances. See microbarm.

A hygrometer in which the sensitive element is a strand or strands of human hair, the length of which is a function of the relative humidity of the air.

The transmission of data collected at a remote location over communications channels to a central station.

The difference between the air temperature and the dew-point. Also called dew-point deficit, dew-point depression.

United Kingdom forecast model. (Available via AccuWeather.com Professional.)

Particle on which the freezing of water occurs.

The average temperature of the air as indicated by a properly exposed thermometer for a given time period, usually a day, a month, or a year.

General name for a type of instrument which measures the inclination of the wind to the horizontal plane. See bivane.

Thermometer for measuring the temperature in the soil at different depths.

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

A very sensitive electrostatic electrometer for measuring small potential differences.

Same as an upper air observation, but commonly used to refer to a single complete radiosonde observation.

That portion of the record of a microbarograph between any two (or a specified small number) of successive crossings of the average pressure level (in the same direction). Analogous to microseism.

Generally, the relative states of inflow, outflow, and storage of moisture over a given area of earth's surface.

See hook gauge.

The lowest temperature that can be obtained on a wet-bulb thermometer in any given sample of air. Obtained by evaporation of water (or ice) from the muslin wick. Used in computing dew point and relative humidity.

Psychrometer to which a small chain or rotary handle is attached so that the observer can rotate the instrument rapidly to properly ventilate the thermometer bulbs.

In general, any object that reflects incident energy. Usually it is a device designed for specific reflection characteristics.

A graphical representation of a frequency distribution. The range of the variable is divided into class intervals for which the frequency of occurrence is represented by a rectangular column. The height of the column is proportional to the frequency of ob ...