For other use, see snow (disambiguation).
Snow, a form of precipitation, is a crystalline form of water ice, consisting of a multitude of snowflakes. Since it is composed of small rough particles, it has an open and therefore soft structure, unless packed by external pressure. It is commonly formed when water vapor sublimates high in the atmosphere and then falls to the ground. Very light snow falling is called flurries or just a flurry.
Snow can be also manufactured using snow cannons, which actually create tiny granules more like sleet. (This is sometimes called "grits" by those in the southern U.S for its likeness to the texture of the food.)
Snowfall varies by time and location, including geographic latitude, elevation and other factors which affect weather in general. In latitudes closer to the equator, there is less chance of snow fall, 35 degrees of northern and southern latitude often quoted as a rough delimiter. The western coasts of the major continents remain snowless to much higher latitudes.
Some mountains, even at or near the equator, have permanent snow cover on their top, including Mauna Kea in Hawaii. Conversely, many regions of the Arctic and Antarctic receive very little precipitation and therefore little snow, despite the bitter cold.
The highest seasonally cumulative precipitation of snow was measured on Mount Rainier during 1971-1972 (a thousand inches); and the highest daily precipitation was recorded in Colorado in 1921 (76 inches).
Substantial snowfall sometimes disrupts infrastructure and services even in regions that are accustomed to them. Traffic may be snarled or even completely stop. Basic infrastructure such as electricity and gap supply can be shut down. A snow day is a day on which school or other services are cancelled owing to unusually heavy snowfall. In areas that normally have very little snow, this may occur even with light accumulation — something often made fun of by those people used to colder climates, where streets would remain passable given the same amount of snow.
Forms of recreation depending on snow:
- many winter sports, such as skiing and snowboarding
- playing with a sled or riding in a sleigh
- building a snowman or snow fort
- throwing snowballs mutually in a snowball fight or at others to tease them.
The concept that no two snowflakes are alike is incorrect: in a volume of snow two feet square by ten inches deep there are roughly one million flakes, and so statistically many snowflakes must be visually identical. The American Meteorological Society has reported that matching snow crystals were discovered by Nancy Knight of the National Center for Atmospheric Research. The crystals were not flakes in the usual sense but rather hollow hexagonal prisms.