The Campbell Scientific PWS100 present weather sensor deployed at the Chilbolton Observatory, Hampshire, detects and classifies precipitation by observing the scattering of a laser beam 20 degrees off the forward direction in the horizontal and vertical planes. The detected signals depend on the size, shape, optical properties, concentration and velocity of the particles. The instrument is mounted approximately 10m above ground on the roof of a cabin at the Chilbolton Observatory site. It is operated continuously. The instrument records counts as a function of size of hydrometeors in 300 bins from 0.1 to 30.0 mm, the number of hydrometeors in 9 type categories. visibility, air temperature, relative humidity, rainfall rate, rainfall accumulation, average hydrometeor velocity, average hydrometeor size and reports the World Meteorological Organisation (WMO) present weather code for the site.