Small ice crystals falling from an apparently cloudless sky, (often, but not always, at night). Crystals originate from air having a higher moisture content above a thermal inversion aloft, where mixing leads to nucleation and growth of crystals at temperatures near âˆ’40Â°C.
Diamond dust is the name commonly used to refer to a ground-level cloud composed of tiny ice crystals. This meteorological phenomenon is also referred to simply as ice crystals and is reported in the METAR code as IC. Diamond dust generally forms under otherwise clear or nearly clear skies, so it is sometimes referred to as clear-sky precipitation.