Frost is a thin layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is similar to the formation of dew, except it occurs below the freezing point of water typically without crossing through a liquid state.
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.
Ice crystals are solid ice in symmetrical shapes including hexagonal columns, hexagonal plates, and dendritic crystals. Ice crystals are responsible for various atmospheric optic displays and cloud formations.
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation; their water vapor does not condense sufficiently to precipitate, so fog and mist do not fall. Two processes, possibly acting together, can lead to air becoming saturated with water vapor: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers.
Black ice, sometimes called clear ice, is a coating of glaze ice on a surface, for example on streets or on lakes. The ice itself is not black, but visually transparent, allowing the often black road below to be seen through it and light to be transmitted. The typically low levels of noticeable ice pellets, snow, or sleet surrounding black ice means that areas of the ice are often next to invisible to drivers or people walking on it. Thus, there is a risk of slippage and subsequent accident due to the unexpected loss of traction.
Rime ice forms when supercooled water droplets freeze onto surfaces. In the atmosphere, there are three basic types of rime ice:
Firn is partially compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé. It is ice that is at an intermediate stage between snow and glacial ice. Firn has the appearance of wet sugar, but has a hardness that makes it extremely resistant to shovelling. Its density generally ranges from 0.35 g/cm3 to 0.9 g/cm3, and it can often be found underneath the snow that accumulates at the head of a glacier.
The 2004 Christmas Eve United States winter storm was a rare weather event that took place in Louisiana and Texas in the United States on December 24, 2004, before the storm moved northeast to affect the coastal sections of the Mid-Atlantic states and New England in the succeeding few days. This was a different storm from the historic event that struck the Midwest and southern Canada around December 23 from another cyclone which preceded this storm. The event involved a thin band of snowfall with unusually cold temperatures for the middle Texas coast, and caused dozens of varied weather records to be shattered. It was the most significant snow for the Texas Gulf Coast, and deep South Texas, since February 1895.
Ice pellets or sleet is a form of precipitation consisting of small, hard, translucent balls of ice. Ice pellets are different from graupel, which is made of frosty white opaque rime, and from a mixture of rain and snow, which is a slushy liquid or semisolid. Ice pellets often bounce when they hit the ground or other solid objects, and make a higher-pitched "tap" when striking objects like jackets, windshields, and dried leaves, compared to the dull splat of liquid raindrops. Pellets generally do not freeze into other solid masses unless mixed with freezing rain. The METAR code for ice pellets is PL.
The Knickerbocker storm was a blizzard on January 27–28, 1922 in the upper South and the middle Atlantic United States. The storm took its name from the resulting collapse of the Knickerbocker Theatre in Washington, D.C., shortly after 9 p.m. on January 28, which killed 98 people and injured 133.
Graupel, also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets in air are collected and freeze on falling snowflakes, forming 2–5 mm (0.08–0.20 in) balls of crisp, opaque rime.
It is very rare for snow to fall in the U.S. state of Florida, especially in the central and southern portions of the state. With the exception of the far northern areas of the state, most of the major cities in Florida have never recorded measurable snowfall, though trace amounts have been recorded, or flurries in the air observed few times each century. According to the National Weather Service, in the Florida Keys and Key West there is no known occurrence of snow flurries since the European colonization of the region more than 300 years ago. In Miami, Fort Lauderdale, and Palm Beach there has been only one known report of snow flurries observed in the air in more than 200 years; this occurred in January 1977. In any event, Miami, Fort Lauderdale, and Palm Beach have not seen snow flurries before or since this 1977 event.
Snowflake Bentley is a children's picture book written by Jacqueline Briggs Martin and illustrated by Mary Azarian. Published in 1998, the book is about Wilson Bentley, the first known photographer of snowflakes. Azarian won the 1999 Caldecott Medal for her illustrations. In 2003, the company Weston Woods Studios, Inc. adapted the book to a film, narrated by Sean Astin. It was released on DVD in 2004.
The subnivean climate is the environment between fallen snow and terrain. This is the environment of many hibernal animals, as it provides insulation and protection from predators. The subnivean climate is formed by three different types of snow metamorphosis: destructive metamorphosis, which begins when snow falls; constructive metamorphosis, the movement of water vapor to the surface of the snowpack; and melt metamorphosis, the melting/sublimation of snow to water vapor and its refreezing in the snowpack. These three types of metamorphosis transform individual snowflakes into ice crystals and create spaces under the snow where small animals can move.
Classifications of snow describe and categorize the attributes of snow-generating weather events, including the individual crystals both in the air and on the ground, and the deposited snow pack as it changes over time. Snow can be classified by describing the weather event that is producing it, the shape of its ice crystals or flakes, how it collects on the ground, and thereafter how it changes form and composition. Depending on the status of the snow in the air or on the ground, a different classification applies.
A snowflake is a single ice crystal that has achieved a sufficient size, and may have amalgamated with others, which falls through the Earth's atmosphere as snow. Each flake nucleates around a tiny particle in supersaturated air masses by attracting supercooled cloud water droplets, which freeze and accrete in crystal form. Complex shapes emerge as the flake moves through differing temperature and humidity zones in the atmosphere, such that individual snowflakes differ in detail from one another, but may be categorized in eight broad classifications and at least 80 individual variants. The main constituent shapes for ice crystals, from which combinations may occur, are needle, column, plate, and rime. Snow appears white in color despite being made of clear ice. This is due to diffuse reflection of the whole spectrum of light by the small crystal facets of the snowflakes.
The December 2010 North American blizzard was a major nor'easter and historic blizzard affecting the Contiguous United States and portions of Canada from December 22–29, 2010. From January 4–15, the system was known as Windstorm Benjamin in Europe. It was the first significant winter storm of the 2010–11 North American winter storm season and the fifth North American blizzard of 2010. The storm system affected the northeast megalopolis, which includes major cities such as Norfolk, Pittsburgh, Philadelphia, Newark, New York City, Hartford, Providence, and Boston. It brought between 12 and 32 inches of snow in many of these areas.
Snow in the southern part of Louisiana presents a rare and serious problem because of South Louisiana’s subtropical climate. For snow to push into the southern region of Louisiana, extreme weather conditions for the area must be present, usually a low-pressure system coupled with unusually low temperatures. Average snowfall in Louisiana is approximately 0.2 inches (5.1 mm) per year, a low figure rivaled only by the states of Florida and Hawaii. Due to the infrequency of these cold weather patterns, southern areas affected in this state are often unprepared to deal with slick streets and freezing temperatures.
Snow science addresses how snow forms, its distribution, and processes affecting how snowpacks change over time. Scientists improve storm forecasting, study global snow cover and its effect on climate, glaciers, and water supplies around the world. The study includes physical properties of the material as it changes, bulk properties of in-place snow packs, and the aggregate properties of regions with snow cover. In doing so, they employ on-the-ground physical measurement techniques to establish ground truth and remote sensing techniques to develop understanding of snow-related processes over large areas.
The January 2019 North American winter storm was a long-lived winter storm, forming as a large area of low pressure off the Pacific Northwest shoreline January 16, making its way to the Northeast by January 21. Its effects included heavy rain/high elevation snow and gusty winds in California, severe weather in the south, near-blizzard conditions in Upstate New York, an ice storm in New England and minor coastal flooding in the Mid-Atlantic.
