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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...)

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A winter service vehicle (WSV), or snow removal vehicle, is used to clear thoroughfares of ice and snow. Winter service vehicles are usually based on dump truck chassis, with adaptations allowing them to carry specially designed snow removal equipment. Many authorities also use smaller vehicles on sidewalks, footpaths, and cycleways. Road maintenance agencies and contractors in temperate or polar areas often own several winter service vehicles, using them to keep the roads clear of snow and ice and safe for driving during winter. Airports use winter service vehicles to keep both aircraft surfaces, and runways and taxiways free of snow and ice, which, besides endangering aircraft takeoff and landing, can interfere with the aerodynamics of the craft.

The earliest winter service vehicles were snow rollers, designed to maintain a smooth, even road surface for sleds, although horse-drawn snowploughs and gritting vehicles are recorded in use as early as 1862. The increase in motor car traffic and aviation in the early 20th century led to the development and popularisation of large motorised winter service vehicles.

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  • ... that the 1st Weather Squadron, the 2016 Weather Squadron of the Year, reports on future battlefield weather conditions and assists during natural disasters?
  • ... that Teikō Shiotani photographed View with Weather Forecast (shown) from his upstairs window, exaggerating the curvature of the horizon by bending the photographic paper under the enlarger?
  • ... that astrophysicist and space-weather specialist Professor Peter T. Gallagher led the building of Ireland's first serious radio telescope, the 3,000-antenna I-LOFAR, at Birr Castle?
  • ... that WILS-TV in Lansing, Michigan, featured a singing weather girl and pianist dressed appropriately for the next day's forecast?
  • ... that Eric Berger wrote about weather for the Houston Chronicle even before he became a certified meteorologist?
  • ... that Canadian ice hockey manager Tubby Schmalz reportedly sheltered visiting teams in his hotel during inclement weather?

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The eye of Hurricane Isabel as seen from the International Space Station.

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...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?

...that a cryoseism is a sudden ground or glacier movement that can occur due to water freezing or ice cracking after drastic temperature changes?

...that BUFR is a binary data format standardized by the World Meteorological Organization for storing observation data from weather stations and weather satellites?

...that the Northwest Weather and Avalanche Center issues weather forecasts for conditions that can cause avalanches in the mountains of western Washington and northwestern Oregon?

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This week in weather history...

April 9

1947: A tornado or series of tornadoes plowed through several towns in Texas, Oklahoma, and Kansas, killing 181 people.

April 10

1996: A wind gust of 408 kilometres per hour (254 mph) was measured by a weather station on Barrow Island, Western Australia, as Cyclone Olivia made landfall. As of 2020 this remains the highest wind gust ever reliably measured.

April 11

1965: The Palm Sunday tornado outbreak, one of the worst in history, produced 78 tornadoes and killed almost 300 people in the American Midwest.

April 12

1934: A wind gust of 231 miles per hour (372 km/h) was measured at the Mount Washington Observatory atop Mount Washington, New Hampshire. At the time, this was the fastest wind speed ever recorded, and it remains the fastest surface wind speed ever measured outside of a tropical cyclone.

April 13

1994: The GOES 8 weather satellite was launched. Part of the Geostationary Operational Environmental Satellite program, GOES 8 would provide weather forecasting data to the United States until its retirement in 2004.

April 14

1999: A severe hailstorm, the costliest disaster in Australian history, dropped hail stones 9 cm (3.5 in) in diameter across the Sydney area. The storm caused more than A$ 2 billion in damage and injured 50 people.

April 15

1927: In New Orleans, 15 inches (380 mm) of rain fell in 18 hours, worsening an already historic flood and leading to the fateful (and ultimately unnecessary) decision to intentionally breach a levee south of the city.

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Vice-Admiral Robert FitzRoy FRS (5 July 1805 – 30 April 1865) was an English officer of the Royal Navy and a scientist. He achieved lasting fame as the captain of HMS Beagle during Charles Darwin's famous voyage, FitzRoy's second expedition to Tierra del Fuego and the Southern Cone.

FitzRoy was a pioneering meteorologist who made accurate daily weather predictions, which he called by a new name of his own invention: "forecasts". In 1854 he established what would later be called the Met Office, and created systems to get weather information to sailors and fishermen for their safety. He was an able surveyor and hydrographer. As Governor of New Zealand, serving from 1843 to 1845, he tried to protect the Māori from illegal land sales claimed by British settlers. (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 Wikipdia's coverage of tropical cyclones.

WikiProject Non-tropical storms is a collaborative project to improve articles related to winter storms, wind storms, and extratropical cyclones.

Wikipedia is a fully collaborative effort by volunteers. So if you see something you think you can improve, be bold and get to editing! We appreciate any help you can provide!

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