Fake You can make fake snow using a common polymer. The fake snow is non-toxic, feels cool to the touch, lasts for days, and looks similar to the real thing. Difficulty: Easy Time Required: mere minutes

Here's How:

1. There are a couple of ways to get the ingredient necessary to make fake polymer snow. You can purchase the fake snow or you can harvest sodium polyacrylate from common household sources. You can find sodium polyacrylate inside disposable diapers or as crystals in a garden center, used to help keep soil moist. 2. All you need to do to make this type of fake snow is add water to the sodium polyacrylate. Add some water, mix the gel. Add more water until you have the desired amount of wetness. The gel will not dissolve. It's just a matter of how 'slushy' you want your snow. 3. Sodium polyacrylate 'snow' feels cool to the touch because it is mainly water. If you want to add more realism to the fake snow, you can refrigerate or freeze it. The gel will not melt. If it dries out, you can rehydrate it by adding water.

Tips:

1. Fake snow is non-toxic, as you would expect from a material used in disposable diapers. However, don't purposely eat it. 'Non-toxic' is not the same as 'good for you'. 2. When you are done playing with fake snow, it's safe to throw it away. 3. If you want yellow snow (or some other color), you can mix food coloring into the fake snow. 4. If you want drier snow, you can reduce the amount of water the polymer can absorb by adding a small amount of salt.

What You Need:

y sodiumpolyacrylate y water

Artificial snow is small particles of ice that are used to increase the amount of snow available for sports such as skiing or snow boarding. It is produced by a machine that uses a high-pressure pump to spray a mist of water into the cold air. The water droplets subsequently crystallize to form fake snow. The first commercially successful machines were developed in the 1950s and improvements in technology have steadily been introduced. With the increase in the popularity of winter sports, the artificial snow market is expected to show significant growth.

Background

The machines that produce artificial snow are designed to mimic the way that natural snow is made. In nature, snowflakes are formed when the temperature falls below 32° F (0° C). Atmospheric water then condenses on particles in the air and crystallizes. This action produces snowflakes that have a variety of sizes and shapes.

In a snow machine, water is first mixed with a nucleating material. It is then pressurized and forced through an atomizing nozzle. This breaks the water up into a mist, which is then injected with compressed air to break it up even further. As it exits the snow machine, the mist crystallizes on the nucleator and turns into tiny snow-like ice particles. Depending on the quality of the snow machine, the artificial snow can be as good as natural snow.

History

Although archeological evidence suggests that humans first skied about 4,000 years ago, interest in this activity as a sport did not begin until the middle of the nineteenth century. In 1883, the first international competition was held in Norway. The sport soon spread to the rest of Europe and America. As the popularity of skiing increased so did the need for a device that could provide snow when it was not naturally available. This need led to the development of the first artificial snow making machines.

One of the first machines was patented in the early 1900s. While it was functional, this machine was crude and unreliable. Steady improvements in design led to the development of a compressed air snow-making machine in the 1950s. This machine worked by using compressed air to force water through a nozzle. The nozzle would break the water up into smaller droplets, which would subsequently crystallize. The Pierce device, named after its inventor, was effective enough that most ski resorts used it. However, it did have its drawbacks, most notably, the nozzle tended to clog and it required a very high amount compressed air. This made it expensive to run. Additionally, the machine was quite noisy, and the snow that it produced tended to be wetter and icier.

During the 1970s, a variety of new innovations were introduced to the machines that improved the quality and method of producing artificial snow. One improvement was the addition of a rotating base and fan. The fan would blow the newly created snow farther away from the machine than compressed air alone and the rotating base allowed the direction of the snow to be changed. This made it possible to cover a much larger area with a single machine. Another improvement was the introduction of a ducted-fan machine. These machines were portable, making it possible to use them all over the ski run. They were superior to compressed air machines because they were significantly quieter and were less expensive to run.

In 1975, a nucleating agent was discovered by Steve Lindow, a graduate student at the University of Wisconsin. While investigating a method to protect plants from frost damage, he found a protein that attracts water molecules and helps them form crystals. It was soon realized that this would be a useful material for making artificial snow. The material was then trademarked and is now sold under the trade name Snomax.

As electronics improved, so did the controls for artificial snow-making machines. Computer controls were added, as were sensors that could automatically detect snow requirements. Higher powered fans were also added. Various other innovations led to machines that could produce better snow and more of it. Today, nearly all ski resorts employ some type of artificial snow-making system to improve skiing conditions and increase the length of the ski .

Raw Materials

Water is the primary ingredient required to make artificial snow. Since ski areas are located on mountains however, finding an appropriate water supply is often a problem. If rivers or creeks are nearby they may be used. Otherwise, ponds or dams are created at the bottom of the mountain to produce a storage supply of water. The water is then pumped to the snow-making machines when needed.

In addition to water, compressed air and a nucleating material are also required to make snow. The compressed air is obtained using a pump. The nucleating agent is a biodegradable protein, which causes water molecules to form crystals at a higher temperature than normal. It is obtained from a nontoxic strain of a bacterium called Pseudomonas syringae. On average, this material can increase the amount of snow produced by a machine by 50%. It also helps produce lighter, drier flakes.

Design

The most important part of any snow-making system is the snow-making machine called a snow cannon or snow gun. A variety of designs are available, however most contain common elements including compressors, pumps, fans, and controls.

A central piece of the snow-making machine is the fan assembly. This part is responsible for converting the air/water mixture into tiny droplets and blowing it out onto the slope. It is similar to a typical portable house fan. It has a rotating propeller blade attached to a variable speed motor. Attached to the blades are curved vanes that direct the flow of air in a linear fashion. The fan is encased in an elongated steel duct that is open on both ends. As the blades of the fan move, air is drawn in from one side of the duct. This side is covered with a screen to prevent foreign objects from entering the assembly. The mechanisms controlling the main ingredients of the snow are located in the front, or discharge end, of the fan duct. This includes a water spray, compressed air pump, and a nucleating device. The nucleating device contains a reservoir filled with a nucleating agent. Water is pumped through this reservoir and the protein is incorporated.

During the snow-making process, the fan assembly is attached to a variety of pieces. To get water and air, hoses are hooked up to the fan assembly. These hoses are connected to a series of compressors and pumps that move air and water through pipes, up the mountain. To increase the coverage of the snow, the fan assembly is mounted on an oscillating stand, or yoke. Depending on the design, the placement of the yoke can be just off the ground or attached to a high tower. Levers may be connected to the yoke, which can adjust the angle at which snow exits the machine. A control box for the machine is typically located at the base of the yoke. This includes switches to operate things such as the water flow, fan rotation, and oscillation speed. The control box may be operated by a remote computer.

The Manufacturing Process

The production of artificial snow requires a series of devices that can move water and air up the mountain, combine them with a nucleating material, and spray them into the air as small droplets. Typically, the system is installed during the months and operated at night after the slopes have closed.

Installation of the system

y Artificial snow making requires an entire system to be installed on the mountain slope. This system includes a series of water pipes, electric cables, pumps, and compressors in addition to the snow making machines. First, plans showing the layout of the system are drawn. Then the water pipes and cables are laid in long trenches traversing the entire slope. The trenches must be dug significantly deep so water does not freeze during the winter months. At various points along the water line, valves and hoses are installed to bring water to the surface. Hay bales are placed around them for protection.

Mixing water with other components

y Snow making is typically done at night and requires constant monitoring. It is typically only done when the outdoor temperature is 28° F (-2.2° C) or below. A number of snow machines are hooked up to the water lines all the way up the slope. When the machines are turned on, the snow making process begins. The water is first pumped up the mountain to the various machines. Depending on the type of machine, water may be mixed with the nucleating material prior to pumping or when it first enters the machine.

Creating the snow

y The water is then mixed with compressed air and pumped through a high powered fan. The fan can spray the mixture nearly 60 ft (18.3 m) into the air. As it leaves the machine, the water crystallizes and forms snow. The snow is piled up is large mounds known as whales. At this point the snow may be analyzed and the machines are adjusted to produce the best quality snow. y When a pile of artificial snow is significantly high, the snow making machine is turned off. At optimal performance, a snow machine can produce enough snow to cover an acre in about 2 hours. The whale is then allowed to set, or cure, for two to three days. This lets excess water drain off and helps produce a softer snow.

Moving the snow

y After the curing process, the snow pile is ready for grooming. Using a special plow, the snow is smoothed out onto the skiing surface. While it is being moved, it is sent through a tilling device. This fluffs up the snow, making it more skiable.

Quality Control

Producing artificial snow that is as good as or better than natural snow requires significant quality control measures. Prior to production, the nucleating material is checked to ensure that it meets the appropriate specifications. While the snow is being made, it is analyzed for crystal quality, appearance, and wetness. The air/water ratio may be adjusted to improve the quality of the snow. If the snow is of the highest quality, it will last longer, hold its shape better, and be easier to groom.

The Future

The shortcomings of the current artificial snow-making technology suggest possible improvements in the future. Currently, the noise generated by these machines is a problem. While attempts have been made to reduce the sound, future machines will be even quieter. Another limitation of the snow-making machines is their narrow temperature range of operation. New machines may be able to produce snow at temperatures over 28° F (-2.2° C). These machines may also produce higher quality snow in less time.

Snow From Wikipedia, the free encyclopedia Jump to: navigation, search "Snowfall" redirects here. For other uses, see Snow (disambiguation) and Snowfall (disambiguation).

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Dry season · St orms · · · Tropical (Hurricane) Winter · · · · P t t recipi a ion · ·Snow · · · T opics · · W th t ea er por al v·d·e

Snow is a form of within the Earth's atmosphere in the form of crystallinewaterice, consisting of a multitude of snowflakes that fall from . Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by external pressure. Snowflakes come in a variety of sizes and shapes. Types which fall in the form of a ball due to melting and refreezing, rather than a flake, are known as graupel, with ice pellets and as examples of graupel. Snowfall amount and its related liquid equivalent precipitation amount are determined using a variety of different rain gauges.

The process of precipitating snow is called snowfall. Snowfall tends to form within regions of upward motion of air around a type of low-pressure system known as an extratropical cyclone. Snow can fall poleward of these systems' associated warm fronts and within their comma head precipitation patterns (called such due to the comma-like shape of the cloud and precipitation pattern around the poleward and west sides of extratropical ). Where relatively warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. is possible within a cyclone's comma head and within lake effect precipitation bands. In mountainous areas, heavy snow is possible where upslope flow is maximized within windward sides of the terrain at elevation, if the atmosphere is cold enough. Forms

Snow on the ground in the mountains of Southern California.

Fresh snow on a thin twig Ȃ Poland

Once on the ground, snow can be categorized as powdery when fluffy, granular when it begins the cycle of melting and refreezing, and eventually ice once it packs down, after multiple melting and refreezing cycles, into a dense mass called snow pack. When powdery, snow moves with the wind from the location where it originally landed, forming deposits called snowdrifts which may have a depth of several meters. After attaching to hillsides, blown snow can evolve into a snow slab, which is an avalanche hazard on steep slopes. The existence of a snowpack keeps temperatures colder than they would be otherwise, as the whiteness of the snow reflects most sunlight, and the absorbed heat goes into melting the snow rather than increasing its temperature. The water equivalent of snowfall is measured to monitor how much liquid is available to flood rivers from meltwater which will occur during the following spring. Snow cover can protect crops from extreme cold. If snowfall stays on the ground for a series of years uninterrupted, the snowpack develops into a mass of ice called glacier. Fresh snow absorbs sound, lowering ambient noise over a landscape because the trapped air between snowflakes attenuates vibration. These acoustic qualities quickly minimize and reverse, once a layer of freezing rain falls on top of snow cover. Walking across snowfall produces a squeaking sound at low temperatures.

The energy balance of the snowpack itself is dictated by several heat exchange processes. The snowpack absorbs solar shortwave radiation that is partially blocked by and reflected by snow surface. A long-wave heat exchange takes place between the snowpack and its surrounding environment that includes overlying air mass, tree cover and clouds. Heat exchange takes place by convection between the snowpack and the overlaying air mass, and it is governed by the temperature gradient and wind speed. Moisture exchange between the snowpack and the overlying air mass is accompanied with latent heat transfer that is influenced by vapor pressure gradient and air wind. Rain on snow can add significant amounts of thermal energy to the snowpack. A generally insignificant heat exchange takes place by conduction between the snowpack and the ground. The small temperature change from before to after a snowfall is a result of the heat transfer between the snowpack and the air.[1]

The term snow storm can describe a heavy snowfall while a blizzard involves snow and wind, obscuring visibility. Snow is a term for an intermittent snowfall, while flurry is used for very light, brief snowfalls. Snow can fall more than a meter at a time during a single storm in flat areas, and meters at a time in rugged terrain, such as mountains. When snow falls in significant quantities, travel by foot, car, airplane and other means becomes highly restricted, but other methods of mobility become possible: the use of snowmobiles, snowshoes and skis. When heavy snow occurs early in the fall, significant damage occurs to trees still in leaf. Areas with significant snow each year can store the winter snow within an ice house, which can be used to cool structures during the following summer. A variation on snow has been observed on Venus, though composed of metallic compounds and occurring at a substantially higher temperature.

[edit]Cause See also: Extratropical cyclone, Lake-effect snow, and Rainband

Preferred region of heavy snowfall ("Banded Snowfall") around the comma head of a wintertime low pressure area, shaded in green in the United States.

Extratropical cyclones can bring cold and dangerous conditions with heavy rain and snow with winds exceeding 119 km/h (74 mph),[2] (sometimes referred to as windstorms in Europe). The band of precipitation that is associated with their warm front is often extensive, forced by weak upward vertical motion of air over the frontal boundary which condenses as it cools and produces precipitation within an elongated band,[3] which is wide and stratiform, meaning falling out of nimbostratus clouds.[4] When moist air tries to dislodge an arctic air mass, overrunning snow can result within the poleward side of the elongated precipitation band. In the Northern Hemisphere, poleward is towards the North Pole, or north. Within the Southern Hemisphere, poleward is towards the South Pole, or south. Within the cold sector, poleward and west of the cyclone center, small scale or mesoscale bands of heavy snow can occur within a cyclone's comma head pattern. The cyclone's comma head pattern is a comma- shaped area of clouds and precipitation found around mature extratropical cyclones. These snow bands typically have a width of 20 miles (32 km) to 50 miles (80 km).[5] These bands in the comma head are associated with areas of frontogenesis, or zones of strengthening temperature contrast.[6]

Lake-effect snow bands near the Korean Peninsula

Southwest of extratropical cyclones, curved cyclonic flow bringing cold air across the relatively warm water bodies can lead to narrow lake-effect snow bands. Those bands bring strong localized snowfall which can be understood as follows: Large water bodies such as lakes efficiently store heat that results in significant temperature differences (larger than 13 °C or 23 °F) between the water surface and the air above.[7] Because of this temperature difference, warmth and moisture are transported upward, condensing into vertically oriented clouds (see satellite picture) which produce snow showers. The temperature decrease with height and cloud depth are directly affected by both the water temperature and the large-scale environment. The stronger the temperature decrease with height, the deeper the clouds get, and the greater the precipitation rate becomes.[8]

In mountainous areas, heavy snowfall accumulates when air is forced to ascend the mountains and squeeze out precipitation along their windward slopes, which in cold conditions, falls in the form of snow. Because of the ruggedness of terrain, forecasting the location of heavy snowfall remains a significant challenge.[9]

[edit]Snowflakes Main article: Snowflake

Snowflakes

Snow crystals form when tiny supercooled cloud droplets (about 10 ȝm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than í18 °C (0 °F), because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus." Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than í35 °C (í31 °F).[10] In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Ice nuclei are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,[11] although to what extent is unclear. Artificial nuclei include particles of silver iodide and dry ice, and these are used to stimulate precipitation in cloud seeding.[12]

Once a droplet has frozen, it grows in the supersaturated environment, which is one where air is saturated with respect to ice when the temperature is below the freezing point. The droplet then grows by diffusion of water molecules in the air (vapor) onto the ice crystal surface where they are collected. Because water droplets are so much more numerous than the ice crystals due to their sheer abundance, the crystals are able to grow to hundreds of micrometers or millimeters in size at the expense of the water droplets by a process known as the Wegner-Bergeron-Findeison process. The corresponding depletion of water vapor causes the ice crystals grow at the droplets' expense. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their mass, and may collide and stick together in clusters, or aggregates. These aggregates are snowflakes, and are usually the type of ice particle that falls to the ground.[13] Guinness World Records list the world¶s largest snowflakes as those of January 1887 at Fort Keogh, Montana; allegedly one measured 38 cm (15 in) wide.[14] Although the ice is clear, scattering of light by the crystal facets and hollows/imperfections mean that the crystals often appear white in color due to diffuse reflection of the whole spectrum of light by the small ice particles.[15]

The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed.[13] The most common snow particles are visibly irregular. Planar crystals (thin and flat) grow in air between 0 °C (32 °F) and í3 °C (27 °F). Between í3 °C (27 °F) and í8 °C (18 °F), the crystals will form needles or hollow columns or prisms (long thin pencil-like shapes). From í8 °C (18 °F) to í22 °C (í8 °F) the shape reverts back to plate-like, often with branched or dendritic features. At temperatures below í22 °C (í8 °F), the crystal development becomes column-like, although many more complex growth patterns also form such as side-planes, bullet-rosettes and also planar types depending on the conditions and ice nuclei.[16][17][18] If a crystal has started forming in a column growth regime, at around í5 °C (23 °F), and then falls into the warmer plate-like regime, then plate or dendritic crystals sprout at the end of the column, producing so called "capped columns."[13]

A snowflake consists of roughly 1019 water molecules, which are added to its core at different rates and in different patterns, depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground. As a result, it is extremely difficult to encounter two identical snowflakes.[19][20] Initial attempts to find identical snowflakes by photographing thousands their images under a microscope from 1885 onward by Wilson Alwyn Bentley found the wide variety of snowflakes we know about today.[21] It is more likely that two snowflakes could become virtually identical if their environments were similar enough. Matching snow crystals were discovered in Wisconsin in 1988. The crystals were not flakes in the usual sense but rather hollow hexagonalprisms.[22]

[edit]Types Main article: Types of snow

Hoar frost that grows on the snow surface due to water vapor moving up through the snow on cold, clear nights

A snow avalanche

Types of snow can be designated by the shape of the flakes, the rate of accumulation, and the way the snow collects on the ground. Types which fall in the form of a ball due to melting and refreezing cycles, rather than a flake, are known as graupel, with ice pellets and snow pellets as types of graupel associated with wintry precipitation.[23][24] Once on the ground, snow can be categorized as powdery when fluffy, granular when it begins the cycle of melting and refreezing, and eventually ice once it packs down into a dense drift after multiple melting and refreezing cycles. When powdery, snow drifts with the wind from the location where it originally fell,[25] forming deposits with a depth of several meters in isolated locations.[26]Snow fences are constructed in order to help control snow drifting in the vicinity of roads, to improve highway safety.[27] After attaching to hillsides, blown snow can evolve into a snow slab, which is an avalanche hazard on steep slopes. A frozen equivalent of dew known as hoar frost forms on a snow pack when winds are light and there is ample low-level moisture over the snow pack.[28]

Snowfall's intensity is determined by visibility. When the visibility is over 1 kilometer (0.62 mi), snow is considered light. Moderate snow describes snowfall with visibility restrictions between 0.5 and 1 km. Heavy snowfall describes conditions when visibility is less than 0.5 km.[29] Steady of significant intensity are often referred to as "snowstorms".[30] When snow is of variable intensity and short duration, it is described as a "snow shower".[31] The term is used to describe the lightest form of a snow shower.[32]

A blizzard is a weather condition involving snow which has varying definitions in different parts of the world. In the United States, a blizzard is occurring when two conditions are met for a period of three hours