A haboob is a type of intense dust storm carried on an atmospheric gravity current known as a weather front. Haboobs occur in dry land area regions throughout the world. During thunderstorm formation, winds move in a direction opposite to the storm's travel, they move from all directions into the thunderstorm; when the storm collapses and begins to release precipitation, wind directions reverse, gusting outward from the storm and gusting the strongest in the direction of the storm's travel. When this downdraft of cold air, or downburst, reaches the ground, it blows dry, loose silt and clay up from the desert, creating a wall of sediment that precedes the storm cloud; this wall of dust can be up to 100 km several kilometers in elevation. At their strongest, haboob winds travel at 35–100 km/h, they may approach with little or no warning. Rain does not appear at ground level as it evaporates in the hot, dry air; the evaporation cools the rushing air further and accelerates it. When the rain does persist, it can contain a considerable quantity of dust.
Severe cases are called mud storms. Eye and respiratory system protection is advisable for anyone. Moving to shelter is advised during a strong event. Haboobs have been observed in the Sahara desert, as well as across the Arabian Peninsula, throughout Kuwait, in the most arid regions of Iraq. Haboob winds in the Arabian Peninsula, Kuwait are created by the collapse of a thunderstorm. African haboobs result from the northward summer shift of the inter-tropical front into North Africa, bringing moisture from the Gulf of Guinea. Haboobs in Australia may be associated with cold fronts; the deserts of Central Australia near Alice Springs, are prone to haboobs, with sand and debris reaching several kilometers into the sky and leaving up to 30 centimetres of sand in the haboob's path. As with haboobs in the Middle East, haboob occurrences in North America are created by the collapse of a thunderstorm; this is a local or mesoscale event, at times of extreme drought they can originate in agricultural regions.
Some of the most famous dust storms of the Dust Bowl and similar conditions were in fact synoptic scale events generated by a strong cold frontal passage, with 14 April 1935, 9–11 May 1934, 19 February 1954, 11 November 1911 being vivid examples. The arid and semiarid regions of North America—in fact, any dry region—may experience haboobs. In North America, the most common terms for these events are sandstorm. In the U. S. they occur in the deserts of Arizona, including around the cities of Yuma and Phoenix. They sometimes occur in the Columbia Basin, of Eastern Washington always leading to an impact with the city of Spokane. If the storms are strong enough, they can reach as far east as Post Falls and Moscow, in North Idaho. Global dust storms on Mars have been compared to haboobs on Earth. Haboob Photos @ HikeArizona. COM Haboobs, Arizona Department of Transportation; the Bibliography of Aeolian Research Haboob on Winds of the World Short Video of the 5 July 2011 Arizona Haboob on YouTube Time-lapse video of the 5 July 2011 Arizona Haboob
Autumn known as fall in American English and sometimes in Canadian English, is one of the four temperate seasons. Autumn marks the transition from summer to winter, in September or March, when the duration of daylight becomes noticeably shorter and the temperature cools considerably. One of its main features in temperate climates is the shedding of leaves from deciduous trees; some cultures regard the autumnal equinox as "mid-autumn", while others with a longer temperature lag treat it as the start of autumn. Meteorologists use a definition based on Gregorian calendar months, with autumn being September and November in the northern hemisphere, March and May in the southern hemisphere. In North America, autumn traditionally starts on September 21 and ends on December 21, it is considered to end with the winter solstice. Popular culture in the United States associates Labor Day, the first Monday in September, as the end of summer and the start of autumn; as daytime and nighttime temperatures decrease, trees shed their leaves.
In traditional East Asian solar term, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the national meteorological service, Met Éireann, are September and November. However, according to the Irish Calendar, based on ancient Gaelic traditions, autumn lasts throughout the months of August and October, or a few days depending on tradition; the names of the months in Manx Gaelic are based on autumn covering August and October. In Argentina and New Zealand, autumn begins on 1 March and ends on 31 May; the word autumn comes from the ancient Etruscan root autu- and has within it connotations of the passing of the year. It was borrowed by the neighbouring Romans, became the Latin word autumnus. After the Roman era, the word continued to be used as the Old French word autompne or autumpne in Middle English, was normalised to the original Latin. In the Medieval period, there are rare examples of its use as early as the 12th century, but by the 16th century, it was in common use.
Before the 16th century, harvest was the term used to refer to the season, as it is common in other West Germanic languages to this day. However, as more people moved from working the land to living in towns, the word harvest lost its reference to the time of year and came to refer only to the actual activity of reaping, autumn, as well as fall, began to replace it as a reference to the season; the alternative word fall for the season traces its origins to old Germanic languages. The exact derivation is unclear, with the Old English fiæll or feallan and the Old Norse fall all being possible candidates. However, these words all have the meaning "to fall from a height" and are derived either from a common root or from each other; the term came to denote the season in 16th-century England, a contraction of Middle English expressions like "fall of the leaf" and "fall of the year". During the 17th century, English emigration to the British colonies in North America was at its peak, the new settlers took the English language with them.
While the term fall became obsolete in Britain, it became the more common term in North America. The name backend, a once common name for the season in Northern England, has today been replaced by the name autumn. Association with the transition from warm to cold weather, its related status as the season of the primary harvest, has dominated its themes and popular images. In Western cultures, personifications of autumn are pretty, well-fed females adorned with fruits and grains that ripen at this time. Many cultures feature autumnal harvest festivals the most important on their calendars. Still extant echoes of these celebrations are found in the autumn Thanksgiving holiday of the United States and Canada, the Jewish Sukkot holiday with its roots as a full-moon harvest festival of "tabernacles". There are the many North American Indian festivals tied to harvest of ripe foods gathered in the wild, the Chinese Mid-Autumn or Moon festival, many others; the predominant mood of these autumnal celebrations is a gladness for the fruits of the earth mixed with a certain melancholy linked to the imminent arrival of harsh weather.
This view is presented in English poet John Keats' poem To Autumn, where he describes the season as a time of bounteous fecundity, a time of'mellow fruitfulness'. In North America, while most foods are harvested during the autumn, foods associated with the season include pumpkins and apples, which are used to make the seasonal beverage apple cider. Autumn in poetry, has been associated with melancholia; the possibilities and opportunities of summer are gone, the chill of winter is on the horizon. Skies turn grey, the amount of usable daylight drops and many people turn inward, both physically and mentally, it has been referred to as an unhealthy season. Similar examples may be found in Irish poet William Butler Yeats' poem The Wild Swans at Coole where the maturing season that the poet observes symbolically represents his own ageing self. Like the natural world that he observes, he too has reached his prime and now must look forward to the inevitability of old age and death. French p
Cumulonimbus is a dense, towering vertical cloud, forming from water vapor carried by powerful upward air currents. If observed during a storm, these clouds may be referred to as thunderheads. Cumulonimbus can form alone, along cold front squall lines; these clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb. Towering cumulonimbus clouds are accompanied by smaller cumulus clouds; the cumulonimbus base may extend several miles across and occupy low to middle altitudes - formed at altitude from 200 to 4,000 m. Peaks reach to as much as 12,000 m, with extreme instances as high as 21,000 m or more. Well-developed cumulonimbus clouds are characterized by a flat, anvil-like top, caused by wind shear or inversion near the tropopause; the shelf of the anvil may precede the main cloud's vertical component for many miles, be accompanied by lightning.
Rising air parcels surpass the equilibrium level and form an overshooting top culminating at the maximum parcel level. When vertically developed, this largest of all clouds extends through all three cloud regions; the smallest cumulonimbus cloud dwarfs its neighbors in comparison. Cumulonimbus calvus: cloud with puffy top, similar to cumulus congestus which it develops from. Cumulonimbus capillatus: cloud with cirrus-like, fibrous-edged top. Arcus: low, horizontal cloud formation associated with the leading edge of thunderstorm outflow. Pannus: accompanied by a lower layer of fractus species cloud forming in precipitation. Pileus: small cap-like cloud over parent cumulonimbus. Velum: a thin horizontal sheet that forms around the middle of a cumulonimbus. Incus: cumulonimbus with flat anvil-like cirriform top caused by wind shear where the rising air currents hit the inversion layer at the tropopause. Mamma or mammatus: consisting of bubble-like protrusions on the underside. Tuba: column hanging from the cloud base which can develop into a funnel cloud or tornado.
They are known to drop low, sometimes just 20 feet above ground level. Flanking line is a line of small cumulonimbus or cumulus associated with severe thunderstorms. Rain: precipitation that reaches the ground as liquid in a precipitation shaft. Virga: precipitation that evaporates before reaching the ground. Cumulonimbus storm cells can produce torrential rain of a convective nature and flash flooding, as well as straight-line winds. Most storm cells die after about 20 minutes, when the precipitation causes more downdraft than updraft, causing the energy to dissipate. If there is enough solar energy in the atmosphere, the moisture from one storm cell can evaporate rapidly—resulting in a new cell forming just a few miles from the former one; this can cause thunderstorms to last for several hours. Cumulonimbus clouds can bring dangerous winter storms which bring lightning and torrential snow. However, cumulonimbus clouds are most common in tropical regions. In general, cumulonimbus require moisture, an unstable air mass, a lifting force in order to form.
Cumulonimbus go through three stages: the developing stage, the mature stage, the dissipation stage. The average thunderstorm has a 24 km diameter. Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through. Clouds form when the dewpoint of water is reached in the presence of condensation nuclei in the troposphere; the atmosphere is a dynamic system, the local conditions of turbulence and other parameters give rise to many types of clouds. Various types of cloud occur enough to have been categorized. Furthermore, some atmospheric processes can make the clouds organize in distinct patterns such as wave clouds or actinoform clouds; these are large-scale structures and are not always identifiable from a single point of view. Atmospheric convection Atmospheric thermodynamics Convective instability Cumulonimbus and aviation Hot tower Pyrocumulonimbus William Rankin Clouds Clouds-Online.com Cloud Atlas with many photos and description of the different cloud genera MetOffice.gov.uk Learn about thunderstorms and how cumulonimbus clouds form
A season is a division of the year marked by changes in weather and amount of daylight. On Earth, seasons result from Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, plants to be dormant. Various cultures define the nature of seasons based on regional variations. During May and July, the Northern Hemisphere is exposed to more direct sunlight because the hemisphere faces the Sun; the same is true of the Southern Hemisphere in November and January. It is Earth's axial tilt that causes the Sun to be higher in the sky during the summer months, which increases the solar flux. However, due to seasonal lag, June and August are the warmest months in the Northern Hemisphere while December and February are the warmest months in the Southern Hemisphere. In temperate and subpolar regions, four seasons based on the Gregorian calendar are recognized: spring, autumn or fall, winter.
The definition of seasons is cultural. In India from the ancient times, six seasons or Ritu based on south Asian religious or cultural calendars are recognised and identified today for the purposes such as agriculture and trade. Ecologists use a six-season model for temperate climate regions which are not tied to any fixed calendar dates: prevernal, estival, serotinal and hibernal. Many tropical regions have monsoon season and the dry season; some have a third mild, or harmattan season. Seasons held special significance for agrarian societies, whose lives revolved around planting and harvest times, the change of seasons was attended by ritual. In some parts of the world, some other "seasons" capture the timing of important ecological events such as hurricane season, tornado season, wildfire season; the most important of these are the three seasons—flood and low water—which were defined by the former annual flooding of the Nile in Egypt. The seasons result from the Earth's axis of rotation being tilted with respect to its orbital plane by an angle of 23.4 degrees.
Regardless of the time of year, the northern and southern hemispheres always experience opposite seasons. This is because during summer or winter, one part of the planet is more directly exposed to the rays of the Sun than the other, this exposure alternates as the Earth revolves in its orbit. For half of the year, the Northern Hemisphere tips toward the Sun, with the maximum amount occurring on about June 21. For the other half of the year, the same happens, but in the Southern Hemisphere instead of the Northern, with the maximum around December 21; the two instants when the Sun is directly overhead at the Equator are the equinoxes. At that moment, both the North Pole and the South Pole of the Earth are just on the terminator, hence day and night are divided between the two hemispheres. Around the March equinox, the Northern Hemisphere will be experiencing spring as the hours of daylight increase, the Southern Hemisphere is experiencing autumn as daylight hours shorten; the effect of axial tilt is observable as the change in day length and altitude of the Sun at solar noon during the year.
The low angle of Sun during the winter months means that incoming rays of solar radiation are spread over a larger area of the Earth's surface, so the light received is more indirect and of lower intensity. Between this effect and the shorter daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres. Compared to axial tilt, other factors contribute little to seasonal temperature changes; the seasons are not the result of the variation in Earth's distance to the Sun because of its elliptical orbit. In fact, Earth reaches perihelion in January, it reaches aphelion in July, so the slight contribution of orbital eccentricity opposes the temperature trends of the seasons in the Northern Hemisphere. In general, the effect of orbital eccentricity on Earth's seasons is a 7% variation in sunlight received. Orbital eccentricity can influence temperatures, but on Earth, this effect is small and is more than counteracted by other factors; this is because the Northern Hemisphere has more land than the Southern, land warms more than sea.
Any noticeable intensification of southern winters and summers due to Earth's elliptical orbit is mitigated by the abundance of water in the Southern Hemisphere. Seasonal weather fluctuations depend on factors such as proximity to oceans or other large bodies of water, currents in those oceans, El Niño/ENSO and other oceanic cycles, prevailing winds. In the temperate and polar regions, seasons are marked by changes in the amount of sunlight, which in turn causes cycles of dormancy in plants and hibernation in animals; these effects vary with proximity to bodies of water. For example, the South Pole is in the middle of the continent of Antarctica and therefore a considerable distance from the moderating influence of the southern oceans; the North Pole is in the Arctic Ocean, thus its temperature extremes are buffered by the water. The result is that the South Pole is colder during the southern winter than the North Pole dur
Arizona is a state in the southwestern region of the United States. It is part of the Western and the Mountain states, it is the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona shares the Four Corners region with Utah and New Mexico. Arizona is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912, coinciding with Valentine's Day. Part of the territory of Alta California in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848; the southernmost portion of the state was acquired in 1853 through the Gadsden Purchase. Southern Arizona is known for its desert climate, with hot summers and mild winters. Northern Arizona features forests of pine, Douglas fir, spruce trees. There are ski resorts in the areas of Flagstaff and Tucson. In addition to the Grand Canyon National Park, there are several national forests, national parks, national monuments.
About one-quarter of the state is made up of Indian reservations that serve as the home of 27 federally recognized Native American tribes, including the Navajo Nation, the largest in the state and the United States, with more than 300,000 citizens. Although federal law gave all Native Americans the right to vote in 1924, Arizona excluded those living on reservations in the state from voting until the state Supreme Court ruled in favor of Native American plaintiffs in Trujillo v. Garley; the state's name appears to originate from an earlier Spanish name, derived from the O'odham name alĭ ṣonak, meaning "small spring", which applied only to an area near the silver mining camp of Planchas de Plata, Sonora. To the European settlers, their pronunciation sounded like "Arissona"; the area is still known as alĭ ṣonak in the O'odham language. Another possible origin is the Basque phrase haritz ona, as there were numerous Basque sheepherders in the area. A native Mexican of Basque heritage established the ranchería of Arizona between 1734 and 1736 in the current Mexican state of Sonora, which became notable after a significant discovery of silver there, c.
1737. There is a misconception. For thousands of years before the modern era, Arizona was home to numerous Native American tribes. Hohokam and Ancestral Puebloan cultures were among the many that flourished throughout the state. Many of their pueblos, cliffside dwellings, rock paintings and other prehistoric treasures have survived, attracting thousands of tourists each year; the first European contact by native peoples was with Marcos de Niza, a Spanish Franciscan, in 1539. He explored parts of the present state and made contact with native inhabitants the Sobaipuri; the expedition of Spanish explorer Coronado entered the area in 1540–1542 during its search for Cíbola. Few Spanish settlers migrated to Arizona. One of the first settlers in Arizona was José Romo de Vivar. Father Kino was the next European in the region. A member of the Society of Jesus, he led the development of a chain of missions in the region, he converted many of the Indians to Christianity in the Pimería Alta in the 1690s and early 18th century.
Spain founded presidios at Tubac in 1752 and Tucson in 1775. When Mexico achieved its independence from the Kingdom of Spain and its Spanish Empire in 1821, what is now Arizona became part of its Territory of Nueva California known as Alta California. Descendants of ethnic Spanish and mestizo settlers from the colonial years still lived in the area at the time of the arrival of European-American migrants from the United States. During the Mexican–American War, the U. S. Army occupied the national capital of Mexico City and pursued its claim to much of northern Mexico, including what became Arizona Territory in 1863 and the State of Arizona in 1912; the Treaty of Guadalupe Hidalgo specified that, in addition to language and cultural rights of the existing inhabitants of former Mexican citizens being considered as inviolable, the sum of US$15 million dollars in compensation be paid to the Republic of Mexico. In 1853, the U. S. acquired the land south below the Gila River from Mexico in the Gadsden Purchase along the southern border area as encompassing the best future southern route for a transcontinental railway.
What is now known as the state of Arizona was administered by the United States government as part of the Territory of New Mexico until the southern part of that region seceded from the Union to form the Territory of Arizona. This newly established territory was formally organized by the Confederate States government on Saturday, January 18, 1862, when President Jefferson Davis approved and signed An Act to Organize the Territory of Arizona, marking the first official use of the name "Territory of Arizona"; the Southern territory supplied the Confederate government with men and equipment. Formed in 1862, Arizona scout companies served with the Confederate States Army duri
A tropical cyclone is a rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, tropical storm, cyclonic storm, tropical depression, cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean. "Cyclone" refers to their winds moving in a circle, whirling round their central clear eye, with their winds blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis effect. Tropical cyclones form over large bodies of warm water, they derive their energy through the evaporation of water from the ocean surface, which recondenses into clouds and rain when moist air rises and cools to saturation.
This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are fueled by horizontal temperature contrasts. Tropical cyclones are between 100 and 2,000 km in diameter; the strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, they form within 5° of the equator. Tropical cyclones are unknown in the South Atlantic due to a strong wind shear and a weak Intertropical Convergence Zone; the African easterly jet and areas of atmospheric instability which give rise to cyclones in the Atlantic Ocean and Caribbean Sea, along with the Asian monsoon and Western Pacific Warm Pool, are features of the Northern Hemisphere and Australia. Coastal regions are vulnerable to the impact of a tropical cyclone, compared to inland regions; the primary energy source for these storms is warm ocean waters, therefore these forms are strongest when over or near water, weaken quite over land.
Coastal damage may be caused by strong winds and rain, high waves, storm surges, the potential of spawning tornadoes. Tropical cyclones draw in air from a large area—which can be a vast area for the most severe cyclones—and concentrate the precipitation of the water content in that air into a much smaller area; this continual replacement of moisture-bearing air by new moisture-bearing air after its moisture has fallen as rain, which may cause heavy rain and river flooding up to 40 kilometres from the coastline, far beyond the amount of water that the local atmosphere holds at any one time. Though their effects on human populations are devastating, tropical cyclones can relieve drought conditions, they carry heat energy away from the tropics and transport it toward temperate latitudes, which may play an important role in modulating regional and global climate. Tropical cyclones are areas of low pressure in the troposphere, with the largest pressure perturbations occurring at low altitudes near the surface.
On Earth, the pressures recorded at the centers of tropical cyclones are among the lowest observed at sea level. The environment near the center of tropical cyclones is warmer than the surroundings at all altitudes, thus they are characterized as "warm core" systems; the near-surface wind field of a tropical cyclone is characterized by air rotating around a center of circulation while flowing radially inwards. At the outer edge of the storm, air may be nearly calm; as air flows radially inward, it begins to rotate cyclonically in order to conserve angular momentum. At an inner radius, air begins to ascend to the top of the troposphere; this radius is coincident with the inner radius of the eyewall, has the strongest near-surface winds of the storm. Once aloft, air flows away from the storm's center; the mentioned processes result in a wind field, nearly axisymmetric: Wind speeds are low at the center, increase moving outwards to the radius of maximum winds, decay more with radius to large radii.
However, the wind field exhibits additional spatial and temporal variability due to the effects of localized processes, such as thunderstorm activity and horizontal flow instabilities. In the vertical direction, winds are strongest near the surface and decay with height within the troposphere. At the center of a mature tropical cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear "eye". Weather in the eye is calm and free of clouds, although the sea may be violent; the eye is circular in shape, is 30–65 km in diameter, though eyes as small as 3 km and as large as 370 km have been observed. The cloudy outer edge of the eye is called the "eyewall"; the eyewall expands outward with height, resembling an arena foo
Severe weather refers to any dangerous meteorological phenomena with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude and atmospheric conditions. High winds, excessive precipitation, wildfires are forms and effects of severe weather, as are thunderstorms, tornadoes, tropical cyclones, extratropical cyclones. Regional and seasonal severe weather phenomena include blizzards, ice storms, duststorms. Meteorologists define severe weather as any aspect of the weather that poses risks to life, property or requires the intervention of authorities. A narrower definition of severe weather is any weather phenomena relating to severe thunderstorms. According to the World Meteorological Organization, severe weather can be categorized into two groups: general severe weather and localized severe weather. Nor'easters, European wind storms, the phenomena that accompany them form over wide geographic areas.
These occurrences are classified as general severe weather. Downbursts and tornadoes are more localized and therefore have a more limited geographic effect; these forms of weather are classified as localized severe weather. The term severe weather is technically not the same phenomenon as extreme weather. Extreme weather describes unusual weather events that are at the extremes of the historical distribution for a given area. Organized severe weather occurs from the same conditions that generate ordinary thunderstorms: atmospheric moisture and instability. A wide variety of conditions cause severe weather. Several factors can convert thunderstorms into severe weather. For example, a pool of cold air aloft may aid in the development of large hail from an otherwise innocuous appearing thunderstorm. However, the most severe hail and tornadoes are produced by supercell thunderstorms, the worst downbursts and derechos are produced by bow echoes. Both of these types of storms tend to form in environments high in wind shear.
Floods, hurricanes and thunderstorms are considered to be the most destructive weather-related [develop models to predict the most frequent and possible locations. This information is used to save lives. Severe thunderstorms can be assessed in three different categories; these are "approaching severe", "severe", "significantly severe". Approaching severe is defined as hail between 1⁄2 to 1 inch diameter or winds between 50 and 58 M. P. H.. In the United States, such storms will warrant a Significant Weather Alert. Severe is defined as hail winds 58 to 75 miles per hour, or an F1 tornado. Significant severe is defined as hail 2 inches in diameter or larger, winds 75 M. P. H. or more, or a tornado of strength EF2 or stronger. Both severe and significant severe events warrant a severe thunderstorm warning from the United States National Weather Service, the Environment Canada, the Australian Bureau of Meteorology, or the Meteorological Service of New Zealand if the event occurs in those countries. If a tornado is occurring or is imminent, the severe thunderstorm warning will be superseded by a tornado warning in the United States and Canada.
A severe weather outbreak is considered to be when ten or more tornadoes, some of which will be long-tracked and violent, many large hail or damaging wind reports occur within one or more consecutive days. Severity is dependent on the size of the geographic area affected, whether it covers hundreds or thousands of square kilometers. High winds are known to cause damage, depending upon their strength. Wind speeds as low as 23 knots may lead to power outages when tree branches fall and disrupt power lines; some species of trees are more vulnerable to winds. Trees with shallow roots are more prone to uproot, brittle trees such as eucalyptus, sea hibiscus, avocado are more prone to branch damage. Wind gusts may cause poorly designed suspension bridges to sway; when wind gusts harmonize with the frequency of the swaying bridge, the bridge may fail as occurred with the Tacoma Narrows Bridge in 1940. Hurricane-force winds, caused by individual thunderstorms, thunderstorm complexes, tornadoes, extratropical cyclones, or tropical cyclones can destroy mobile homes and structurally damage buildings with foundations.
Winds of this strength due to downslope winds off terrain have been known to shatter windows and sandblast paint from cars. Once winds exceed 135 knots within strong tropical cyclones and tornadoes, homes collapse, significant damage is done to larger buildings. Total destruction to man-made structures occurs; the Saffir–Simpson scale for cyclones and Enhanced Fujita scale for tornados were developed to help estimate wind speed from the damage they cause. A dangerous rotating column of air in contact with both the surface of the earth and the base of a cumulonimbus cloud or a cumulus cloud, in rare cases. Tornadoes come in many sizes but form a visible condensation funnel whose narrowest end reaches the earth and surrounded by a cloud of debris and dust. Tornadoes' wind speeds average between 40 miles per hour and 110 miles per hour, they are 250 feet across and travel a few miles before dissipating. Some attain wind speeds in excess of 300 miles per hour (480