freezing

Freezing or frost occurs when the air temperature falls below the freezing point of water (0 °C, 32 °F, 273 K). This is usually measured at the height of 1.2 metres above the ground surface. There exist some scales defining several degrees of frost severity (from "slight" to "very severe") but they depend on location thus the usual temperatures occurring in winter. The primary symptom of frost weather is that water freezes. If the temperature is low for sufficiently long time, freezing will occur with some delay in lakes, rivers, and the sea. It can occur even in water supply networks, although this is highly undesirable and efforts are made to prevent this from happening. Terminology The English word "frost" has 2 base meanings that are related to each other but nevertheless sufficiently different: temperature of air below the freezing point of water (ca 273 K) deposit of ice on cold surfaces The WMO avoids the word "frost" alone and uses "freezing" for temperature of air below the freezing point of water "hoar frost" and "ground frost" for deposit of ice on cold surfaces (see Hoar frost)