Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the troposphere, just below the stratosphere. Weather refers to day-to-day temperature, precipitation, and other atmospheric conditions, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time. When used without qualification, "weather" is generally understood to mean the weather of Earth.
Weather is driven by air pressure, temperature, and moisture differences between one place and another. These differences can occur due to the Sun's angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the Hadley cell, the Ferrel cell, the polar cell, and the jet stream. Weather systems in the middle latitudes, such as extratropical cyclones, are caused by instabilities of the jet streamflow. Because Earth's axis is tilted relative to its orbital plane (called the ecliptic), sunlight is incident at different angles at different times of the year. On Earth's surface, temperatures usually range ±40 °C (−40 °F to 104 °F) annually. Over thousands of years, changes in Earth's orbit can affect the amount and distribution of solar energy received by Earth, thus influencing long-term climate and global climate change.
Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes, as most atmospheric heating is due to contact with the Earth's surface while radiative losses to space are mostly constant. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Earth's weather system is a chaotic system; as a result, small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout history, and there is evidence that human activities such as agriculture and industry have modified weather patterns.
Studying how the weather works on other planets has been helpful in understanding how weather works on Earth. A famous landmark in the Solar System, Jupiter's Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years. However, the weather is not limited to planetary bodies. A star's corona is constantly being lost to space, creating what is essentially a very thin atmosphere throughout the Solar System. The movement of mass ejected from the Sun is known as the solar wind. (Full article...)
The 1999 Sydney hailstorm was the costliest natural disaster in Australian history, causing extensive damage along the east coast of New South Wales. The storm developed south of Sydney on the afternoon of April 14, 1999 and struck the city's eastern suburbs, including the central business district, later that evening.
The storm dropped an estimated 500,000 tonnes of hailstones in its path. Insured damages caused by the storm were over A$1.7 billion, with the total damage bill (including uninsured damages) estimated to be around A$2.3 billion, equivalent to US$1.5 billion. It was the costliest in Australian history in terms of insured damages, overtaking the 1989 Newcastle earthquake that had resulted in A$1.1 billion in insured damages. Lightning also claimed one life during the storm, and the event caused approximately 50 injuries.
The storm was classified as a supercell following further analysis of its erratic nature and extreme attributes. During the event, the Bureau of Meteorology was consistently surprised at the frequent changes in direction, as well as the severity of the hail and the duration of the storm. The event was very unusual, as the time of year and weather conditions in the region were not conducive for a severe thunderstorm to form.
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Cyclone Gafilo was both the most intense tropical cyclone ever recorded in the South-West Indian Ocean and the most intense tropical cyclone worldwide in 2004. This image was take by the Moderate Resolution Imaging Spectroradiometer on the Terra Earth Observing System satellite on March 6, 2004 as the storm approached northeastern Madagascar. Gafilo would go on to kill more than 300 people in the country.
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...that the Flying river is the name given to the transport of water vapor from the Amazon rainforest to southern Brazil?
...that hurricane shutters are required for all homes in Florida unless impact-resistant glass is used?
...that the Joint Institute for Marine and Atmospheric Research is a combined weather and ocean research institute with the cooperation of the Office of Oceanic and Atmospheric Research and the University of Hawaiʻi?
...that the SS Central America was sunk by a hurricane while carrying more than 30,000 pounds (13,600 kg) of gold, contributing to the Panic of 1857?
...that a hurricane force wind warning is issued by the United States National Weather Service for storms that are not tropical cyclones but are expected to produce hurricane-force winds (65 knots (75 mph; 120 km/h) or higher)?
...that the Automated Tropical Cyclone Forecasting System is a software package for tropical cyclone forecasting developed in 1988 that is still used today by meteorologists in various branches of the US Government?
1812: A tropical cyclone was sighted near Jamaica. This storm would eventually strike New Orleans as a major hurricane, killing around 100 people.
2008: A tornado outbreak began in southern and central Poland, killing 4 people and damaging hundreds of buildings.
1950: Hurricane Hiki reached peak intensity as it passed north of Hawaii. At least 52 inches (1,300 mm) of rain was measured on Kauai; the number may have been higher, as the rain gauge overflowed.
1915: A major hurricane struck the Galveston, Texas area, killing more than 200 people. However, due to the newly-constructed seawall, only 11 died in Galveston itself.
1997: Typhoon Winnie, a storm with an extremely large eye more than 200 miles (320 km) in diameter, made landfall in Zhejiang, China, killing more than 300 people.
1991: Hurricane Bob made landfall in eastern New England, causing more than $2 billion (2006 USD) in damage.
1886: An intense hurricane completely destroyed the port of Indianola, Texas, leading to the town's relocation further inland.
Robert H. Simpson (November 19, 1912 – December 18, 2014) was an American meteorologist, hurricane specialist, first director of the National Hurricane Research Project (NHRP) from 1955 to 1959, and a former director (1967–1974) of the National Hurricane Center (NHC). He was the co-developer of the Saffir–Simpson Hurricane Scale with Herbert Saffir. His wife was Joanne Simpson. (Full article...)
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The scope of WikiProject Weather is to have a single location for all weather-related articles on Wikipedia.
WikiProject Meteorology is a collaborative effort by dozens of Wikipedians to improve the quality of meteorology- and weather-related articles. If you would like to help, visit the project talk page, and see what needs doing.
WikiProject Severe weather is a similar project specific to articles about severe weather. Their talk page is located here.
WikiProject Tropical cyclones is a daughter project of WikiProject meteorology. The dozens of semi-active members and several full-time members focus on improving Wikipedia's coverage of tropical cyclones.
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