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62-499: A more precise definition is given by the Köppen climate classification , which treats steppe climates ( BSh and BSk ) as intermediates between desert climates (BW) and humid climates (A, C, D) in ecological characteristics and agricultural potential. Semi-arid climates tend to support short, thorny or scrubby vegetation and are usually dominated by either grasses or shrubs as they usually cannot support forests. To determine if

124-633: A glacier may form. Otherwise, snow typically melts seasonally, causing runoff into streams and rivers and recharging groundwater . Major snow-prone areas include the polar regions , the northernmost half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture and cold temperatures. In the Southern Hemisphere , snow is confined primarily to mountainous areas, apart from Antarctica . Snow affects such human activities as transportation : creating

186-401: A rainband ), when temperature is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at places which the line passes over as the wind causes intense blowing snow. This type of snowsquall generally lasts less than 30 minutes at any point along its path, but the motion of the line can cover large distances. Frontal squalls may form

248-461: A tropical savanna climate or a humid subtropical climate . These climates tend to have hot, or sometimes extremely hot, summers and warm to cool winters, with some to minimal precipitation. Hot semi-arid climates are most commonly found around the fringes of subtropical deserts. Hot semi-arid climates are most commonly found in Africa , Australia , and South Asia . In Australia, a large portion of

310-433: A cirque (corrie or cwm), a typically armchair-shaped geological feature, which collects snow and where the snowpack compacts under the weight of successive layers of accumulating snow, forming névé. Further crushing of the individual snow crystals and reduction of entrapped air in the snow turns it into glacial ice. This glacial ice will fill the cirque until it overflows through a geological weakness or an escape route, such as

372-649: A crystal morphology diagram, relating crystal shapes to the temperature and moisture conditions under which they formed, which is summarized in the following table. Dendrites Hollow prisms Needles Solid plates Dendrites Solid plates Prisms Nakaya discovered that the shape is also a function of whether the prevalent moisture is above or below saturation. Forms below the saturation line tend more toward solid and compact while crystals formed in supersaturated air tend more toward lacy, delicate, and ornate. Many more complex growth patterns also form, which include side-planes, bullet-rosettes, and planar types, depending on

434-447: A droplet has frozen, it grows in the supersaturated environment—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, the crystals are able to grow to hundreds of micrometers or millimeters in size at

496-589: A few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice. The droplet freezes around this "nucleus". 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 cloud condensation nuclei on which liquid droplets form. Clays, desert dust, and biological particles can be nuclei. Artificial nuclei include particles of silver iodide and dry ice , and these are used to stimulate precipitation in cloud seeding . Once

558-568: A hemisphere's fall , winter, and spring, the atmosphere over continents can be cold enough through the depth of the troposphere to cause snowfall. In the Northern Hemisphere, the northern side of the low-pressure area produces the most snow. For the southern mid-latitudes , the side of a cyclone that produces the most snow is the southern side. A cold front , the leading edge of a cooler mass of air, can produce frontal snowsqualls —an intense frontal convective line (similar to

620-485: A highly porous, sintered material made up of a continuous ice structure and a continuously connected pore space, forming together the snow microstructure". Almost always near its melting temperature, a snowpack is continually transforming these properties wherein all three phases of water may coexist, including liquid water partially filling the pore space. After deposition, snow progresses on one of two paths that determine its fate, either by ablation (mostly by melting) from

682-470: A larger weather system. The physics of snow crystal development in clouds results from a complex set of variables that include moisture content and temperatures. The resulting shapes of the falling and fallen crystals can be classified into a number of basic shapes and combinations thereof. Occasionally, some plate-like, dendritic and stellar-shaped snowflakes can form under clear sky with a very cold temperature inversion present. Snow clouds usually occur in

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744-432: A location has a semi-arid climate, the precipitation threshold must first be determined. The method used to find the precipitation threshold (in millimeters): If the area's annual precipitation in millimeters is less than the threshold but more than half or 50% the threshold, it is classified as a BS (steppe, semi-desert, or semi-arid climate). Furthermore, to delineate hot semi-arid climates from cold semi-arid climates,

806-408: A mean annual temperature of 18 °C (64.4 °F) is used as an isotherm. A location with a BS -type climate is classified as hot semi-arid ( BSh ) if its mean temperature is above this isotherm, and cold semi-arid ( BSk ) if not. Hot semi-arid climates (type "BSh") tend to be located from the high teens to mid-30s latitudes of the tropics and subtropics , typically in proximity to regions with

868-435: A minimum extent of 2 million square kilometres (0.77 × 10 ^  sq mi) each August to a maximum extent of 45 million square kilometres (17 × 10 ^  sq mi) each January or nearly half of the land surface in that hemisphere. A study of Northern Hemisphere snow cover extent for the period 1972–2006 suggests a reduction of 0.5 million square kilometres (0.19 × 10 ^  sq mi) over

930-530: A mountain range results in adiabatic cooling, and ultimately condensation and precipitation. Moisture is gradually removed from the air by this process, leaving drier and warmer air on the descending, or leeward , side. The resulting enhanced snowfall, along with the decrease in temperature with elevation, combine to increase snow depth and seasonal persistence of snowpack in snow-prone areas. Mountain waves have also been found to help enhance precipitation amounts downwind of mountain ranges by enhancing

992-488: A series of snow events, punctuated by freezing and thawing, over areas that are cold enough to retain snow seasonally or perennially. Major snow-prone areas include the Arctic and Antarctic , the Northern Hemisphere, and alpine regions. The liquid equivalent of snowfall may be evaluated using a snow gauge or with a standard rain gauge , adjusted for winter by removal of a funnel and inner cylinder. Both types of gauges melt

1054-409: A short distance ahead of the surface cold front or behind the cold front where there may be a deepening low-pressure system or a series of trough lines which act similar to a traditional cold frontal passage. In situations where squalls develop post-frontally, it is not unusual to have two or three linear squall bands pass in rapid succession separated only by 25 miles (40 kilometers), with each passing

1116-419: A snow fall or seasonal snowpack, or by transitioning from firn (multi-year snow) into glacier ice . Over the course of time, a snowpack may settle under its own weight until its density is approximately 30% of water. Increases in density above this initial compression occur primarily by melting and refreezing, caused by temperatures above freezing or by direct solar radiation. In colder climates, snow lies on

1178-608: A snowpack can create flow fingers and ponding or flow along capillary barriers, which can refreeze into horizontal and vertical solid ice formations within the snowpack. Among the measurements of the properties of snowpacks that the International Classification for Seasonal Snow on the Ground includes are: snow height, snow water equivalent, snow strength, and extent of snow cover. Each has a designation with code and detailed description. The classification extends

1240-416: A snowslide or snowslip) is a rapid flow of snow down a sloping surface. Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack (slab avalanche) when the forces on the snow exceed its strength but sometimes only with gradually widening (loose snow avalanche). After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow. If

1302-630: A substance denser than névé , yet less dense and hard than glacial ice . Firn resembles caked sugar and is very resistant to shovelling. Its density generally ranges from 550 to 830 kilograms per cubic metre (34 to 52 lb/cu ft), and it can often be found underneath the snow that accumulates at the head of a glacier . The minimum altitude that firn accumulates on a glacier is called the firn limit , firn line or snowline . There are four main mechanisms for movement of deposited snow: drifting of unsintered snow, avalanches of accumulated snow on steep slopes, snowmelt during thaw conditions, and

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1364-472: Is "the transformation that the snow undergoes in the period from deposition to either melting or passage to glacial ice". Starting as a powdery deposition, snow becomes more granular when it begins to compact under its own weight, be blown by the wind, sinter particles together and commence the cycle of melting and refreezing. Water vapor plays a role as it deposits ice crystals, known as hoar frost , during cold, still conditions. During this transition, snow "is

1426-685: Is an example of a steppe region in North America outside of the Great Plains. In South America , cold steppe can be found in Patagonia and much of the high elevation regions east of the southern Andes . Relatively small steppe areas can be found in the interior of the South Island of New Zealand . In Australia , a moderately sized temperate steppe region exists in the northern and northwest regions of Victoria , extending to

1488-684: Is another steppe region in Central Europe , centered in Hungary but also including portions of Slovakia , Poland , Ukraine , Romania , Serbia , Croatia , Slovenia , and Austria . Another large steppe area ( prairie ) is located in the central United States , western Canada and the northern part of Mexico . The shortgrass prairie steppe is the westernmost part of the Great Plains region. The Columbia Plateau in southern British Columbia , Oregon , Idaho , and Washington state ,

1550-967: Is found in Eastern Europe and Central Asia , and neighbouring countries stretching from Ukraine in the west through Russia , Kazakhstan , Turkmenistan and Uzbekistan to the Altai , Koppet Dag and Tian Shan ranges in China . The Eurasian Steppe is speculated by David W. Anthony to have had a role in the spread of the horse, the wheel and Indo-European languages . In the Eurasian steppe, soils often consist of chernozem . The inner parts of Anatolia in Turkey , Central Anatolia and East Anatolia in particular and also some parts of Southeast Anatolia , as well as much of Armenia and Iran are largely dominated by cold steppe. The Pannonian Plain

1612-429: Is not a requirement, as blowing snow can create a ground blizzard . Snowstorm intensity may be categorized by visibility and depth of accumulation. Snowfall's intensity is determined by visibility , as follows: Snowsqualls may deposit snow in bands that extend from bodies of water as lake-event weather or result from the passage of an upper-level front. The International Classification for Seasonal Snow on

1674-464: Is termed ocean-effect or bay-effect snow . The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation which may deposit at a rate of many inches of snow each hour, often resulting in a large amount of total snowfall. The areas affected by lake-effect snow are called snowbelts . These include areas east of

1736-554: Is usually covered with grass and shrubs , depending on the season and latitude . The term steppe climate denotes a semi-arid climate , which is encountered in regions too dry to support a forest , but not dry enough to be a desert . Steppes are usually characterized by a semi-arid or continental climate. Extremes can be recorded in the summer of up to 45 °C (115 °F) and in winter of down to −55 °C (−65 °F). Besides this major seasonal difference, fluctuations between day and night are also significant. In both

1798-755: The ABC Islands , the rain shadows of Hispaniola 's mountain ranges in the Dominican Republic and Haiti , parts of the Southwestern United States including California's Central Valley , and sections of South America such as the sertão , the Gran Chaco , and the poleward side of the arid deserts, where they typically feature a Mediterranean precipitation pattern, with generally rainless summers and wetter winters. They are also found in few areas of Europe surrounding

1860-645: The Great Lakes , the west coasts of northern Japan, the Kamchatka Peninsula in Russia, and areas near the Great Salt Lake , Black Sea , Caspian Sea , Baltic Sea , and parts of the northern Atlantic Ocean. Orographic or relief snowfall is created when moist air is forced up the windward side of mountain ranges by a large-scale wind flow. The lifting of moist air up the side of

1922-672: The Levant . In Australia , subtropical steppe can be found in a belt surrounding the most severe deserts of the continent and around the Musgrave Ranges . In North America this environment is typical of transition areas between zones with a Mediterranean climate and true deserts, such as Reno, Nevada , the inner part of California , and much of western Texas and adjacent areas in Mexico. Snowfall Snow comprises individual ice crystals that grow while suspended in

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1984-901: The Mediterranean area also hosts the same steppe-like vegetation, such as the Algerian-Moroccan Hautes Plaines and by extension the North Saharan steppe and woodlands . In Asia , a subtropical steppe can be found in semi-arid lands that fringe the Thar Desert of the Indian subcontinent as well as much of the Deccan Plateau in the rain shadow of the Western Ghats , and the Badia of

2046-594: The Mediterranean Basin . In Europe, BSh climates are predominantly found in southeastern Spain . It can also be found primarily in parts of south Greece but also in marginal areas of Thessaloniki and Chalkidiki in north Greece , most of Formentera , marginal areas of Ibiza and marginal areas of Italy in Sicily , Sardinia and Lampedusa . Cold semi-arid climates (type "BSk") tend to be located in elevated portions of temperate zones generally from

2108-520: The Outback surrounding the central desert regions lies within the hot semi-arid climate region. In South Asia, both India and parts of Pakistan experience the seasonal effects of monsoons and feature short but well-defined wet seasons , but are not sufficiently wet overall to qualify as either a tropical savanna or a humid subtropical climate. Hot semi-arid climates can be also found in parts of North America , such as most of northern Mexico ,

2170-552: 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. Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in

2232-411: The movement of glaciers after snow has persisted for multiple years and metamorphosed into glacier ice. When powdery snow drifts with the wind from the location where it originally fell, forming deposits with a depth of several meters in isolated locations. After attaching to hillsides, blown snow can evolve into a snow slab, which is an avalanche hazard on steep slopes. An avalanche (also called

2294-648: The 35-year period. The following are world records regarding snowfall and snowflakes: The cities (more than 100,000 inhabitants) with the highest annual snowfall are Aomori (792 cm), Sapporo (485 cm) and Toyama (363 cm) in Japan , followed by St. John's (332 cm) and Quebec City (315 cm) in Canada , and Syracuse, NY (325 cm). According to the International Association of Cryospheric Sciences, snow metamorphism

2356-460: The Ground defines "height of new snow" as the depth of freshly fallen snow, in centimeters as measured with a ruler, that accumulated on a snowboard during an observation period of 24 hours, or other observation interval. After the measurement, the snow is cleared from the board and the board is placed flush with the snow surface to provide an accurate measurement at the end of the next interval. Melting, compacting, blowing and drifting contribute to

2418-413: The accumulated snow and report the amount of water collected. At some automatic weather stations an ultrasonic snow depth sensor may be used to augment the precipitation gauge. Snow flurry , snow shower , snow storm and blizzard describe snow events of progressively greater duration and intensity. A blizzard is a weather condition involving snow and has varying definitions in different parts of

2480-425: The atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles, columns and rime . As snow accumulates into a snowpack , it may blow into drifts. Over time, accumulated snow metamorphoses, by sintering , sublimation and freeze-thaw . Where the climate is cold enough for year-to-year accumulation,

2542-458: The avalanche moves fast enough some of the snow may mix with the air forming a powder snow avalanche, which is a type of gravity current . They occur in three major mechanisms: Many rivers originating in mountainous or high-latitude regions receive a significant portion of their flow from snowmelt. This often makes the river's flow highly seasonal resulting in periodic flooding during the spring months and at least in dry mountainous regions like

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2604-448: The conditions and ice nuclei. If a crystal has started forming in a column growth regime at around −5 °C (23 °F) and then falls into the warmer plate-like regime, plate or dendritic crystals sprout at the end of the column, producing so called "capped columns". Magono and Lee devised a classification of freshly formed snow crystals that includes 80 distinct shapes. They documented each with micrographs. Snow accumulates from

2666-475: The context of larger weather systems, the most important of which is the low-pressure area, which typically incorporate warm and cold fronts as part of their circulation. Two additional and locally productive sources of snow are lake-effect (also sea-effect) storms and elevation effects, especially in mountains. Mid-latitude cyclones are low-pressure areas which are capable of producing anything from cloudiness and mild snow storms to heavy blizzards . During

2728-544: The contribution of snowmelt to river hydraulics and ground hydrology . In doing so, they employ a variety of instruments to observe and measure the phenomena studied. Their findings contribute to knowledge applied by engineers , who adapt vehicles and structures to snow, by agronomists , who address the availability of snowmelt to agriculture , and those, who design equipment for sporting activities on snow. Scientists develop and others employ snow classification systems that describe its physical properties at scales ranging from

2790-450: 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. Micrography of thousands of snowflakes from 1885 onward, starting with Wilson Alwyn Bentley , revealed the wide diversity of snowflakes within a classifiable set of patterns. Closely matching snow crystals have been observed. Ukichiro Nakaya developed

2852-446: The difficulty of measuring snowfall. Glaciers with their permanent snowpacks cover about 10% of the earth's surface, while seasonal snow covers about nine percent, mostly in the Northern Hemisphere, where seasonal snow covers about 40 million square kilometres (15 × 10 ^  sq mi), according to a 1987 estimate. A 2007 estimate of snow cover over the Northern Hemisphere suggested that, on average, snow cover ranges from

2914-483: The expense of the water droplets by the Wegener–Bergeron–Findeisen process . 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. Although the ice is clear, scattering of light by

2976-442: The gap between two mountains. When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure. On steeper slopes, this can occur with as little as 15 m (49 ft) of snow-ice. Scientists study snow at a wide variety of scales that include the physics of chemical bonds and clouds ; the distribution, accumulation, metamorphosis, and ablation of snowpacks; and

3038-453: The ground all winter. By late spring, snow densities typically reach a maximum of 50% of water. Snow that persists into summer evolves into névé , granular snow, which has been partially melted, refrozen and compacted. Névé has a minimum density of 500 kilograms per cubic metre (31 lb/cu ft), which is roughly half of the density of liquid water. Firn is snow that has persisted for multiple years and has been recrystallized into

3100-678: The highlands of Mongolia and northern Nevada , 30 °C (85 °F) can be reached during the day with sub-freezing readings at night. Steppes average 250–500 mm (10–20 in) of annual precipitation and feature hot summers and cold winters when located in mid-latitudes. In addition to the precipitation level, its combination with potential evapotranspiration defines a steppe climate. Steppe can be classified by climate: It can also be classified by vegetation type, e.g. shrub-steppe and alpine-steppe . The world's largest steppe region, often referred to as "the Great Steppe ",

3162-445: The individual crystal to the aggregated snowpack. A sub-specialty is avalanches , which are of concern to engineers and outdoors sports people, alike. 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

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3224-615: The lift needed for condensation and precipitation. A snowflake consists of roughly 10 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, snowflakes differ from each other though they follow similar patterns. Snow crystals form when tiny supercooled cloud droplets (about 10  μm in diameter) freeze . These droplets are able to remain liquid at temperatures lower than −18 °C (0 °F), because to freeze,

3286-563: 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. In the field snow scientists often excavate a snow pit within which to make basic measurements and observations. Observations can describe features caused by wind, water percolation, or snow unloading from trees. Water percolation into

3348-525: The mid-30s to low 50s latitudes, typically bordering a humid continental climate or a Mediterranean climate . They are also typically found in continental interiors some distance from large bodies of water. Cold semi-arid climates usually feature warm to hot dry summers, though their summers are typically not quite as hot as those of hot semi-arid climates. Unlike hot semi-arid climates, areas with cold semi-arid climates tend to have cold and possibly freezing winters. These areas usually see some snowfall during

3410-502: The mountain West of the US or most of Iran and Afghanistan , very low flow for the rest of the year. In contrast, if much of the melt is from glaciated or nearly glaciated areas, the melt continues through the warm season, with peak flows occurring in mid to late summer. Glaciers form where the accumulation of snow and ice exceeds ablation. The area in which an alpine glacier forms is called

3472-409: The need for keeping roadways, wings, and windows clear; agriculture : providing water to crops and safeguarding livestock; sports such as skiing , snowboarding , and snowmachine travel; and warfare . Snow affects ecosystems , as well, by providing an insulating layer during winter under which plants and animals are able to survive the cold. Snow develops in clouds that themselves are part of

3534-401: The same point roughly 30 minutes apart. In cases where there is a large amount of vertical growth and mixing, the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder which is dubbed thundersnow . A warm front can produce snow for a period as warm, moist air overrides below-freezing air and creates precipitation at the boundary. Often, snow transitions to rain in

3596-589: The southern and mid regions of New South Wales . This area borders the semi-arid and arid Australian Outback which is found farther inland on the continent. In Europe , some Mediterranean areas have a steppe-like vegetation, such as central Sicily in Italy , southern Portugal , parts of Greece in the southern Athens area, and central-eastern Spain , especially the southeastern coast (around Murcia ), and places cut off from adequate moisture due to rain shadow effects such as Zaragoza . In northern Africa ,

3658-406: The warm sector behind the front. Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water, warming the lower layer of air which picks up water vapor from the lake, rises up through the colder air above, freezes, and is deposited on the leeward (downwind) shores. The same effect occurring over bodies of salt water

3720-652: The western US, as well as the Middle East and other parts of Asia. However, they can also be found in Northern Africa, South Africa, sections of South America, sections of interior southern Australia (e.g. Kalgoorlie and Mildura ) and southern New Zealand ( Alexandra ) and sections of Europe. Steppe In physical geography , a steppe ( / s t ɛ p / ) is an ecoregion characterized by grassland plains without closed forests except near rivers and lakes. Steppe biomes may include: A steppe

3782-794: The winter, though snowfall is much lower than at locations at similar latitudes with more humid climates. Areas featuring cold semi-arid climates tend to have higher elevations than areas with hot semi-arid climates, and tend to feature major temperature swings between day and night, sometimes by as much as 20 °C (36 °F) or more. These large diurnal temperature variations are seldom seen in hot semi-arid climates. Cold semi-arid climates at higher latitudes tend to have dry winters and wetter summers, while cold semi-arid climates at lower latitudes tend to have precipitation patterns more akin to Mediterranean climates , with dry summers, relatively wet winters, and even wetter springs and autumns. Cold semi-arid climates are most commonly found in central Asia and

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3844-551: The world. In the United States , a blizzard occurs when two conditions are met for a period of three hours or more: a sustained wind or frequent gusts to 35 miles per hour (16 m/s), and sufficient snow in the air to reduce visibility to less than 0.4 kilometers (0.25 mi). In Canada and the United Kingdom , the criteria are similar. While heavy snowfall often occurs during blizzard conditions, falling snow

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