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Thunderstorm near Garajau, Madeira

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. Most weather phenomena occur in the lowest level of the atmosphere, the troposphere, just below the stratosphere. Weather refers to day-to-day temperature and precipitation activity, 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 mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. On Earth's surface, temperatures usually range ±40 °C (−40 °F to 100 °F) annually. Over thousands of years, changes in Earth's orbit can affect the amount and distribution of solar energy received by the 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. The 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, 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.

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Hurricane Mitch 1998 oct 26 2028Z.jpg
Hurricane Mitch was one of the deadliest and most powerful hurricanes on record in the Atlantic basin, with maximum sustained winds of 180 mph (285 km/h). At the time, Hurricane Mitch was the strongest Atlantic hurricane observed in the month of October, though it has since been surpassed by Hurricane Wilma of the 2005 season. Hurricane Mitch dropped historic amounts of rainfall in Honduras and Nicaragua, with unofficial reports of up to 75 inches (1900 mm). Deaths due to catastrophic flooding made it the second deadliest Atlantic hurricane in history; nearly 11,000 people were killed with over 8,000 left missing by the end of 1998. The flooding caused extreme damage, estimated at over $5 billion (1998 USD, $6.5 billion 2008 USD)...

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Did you know...

...that the Oklahoma Mesonet is a network of 121 weather instruments across US state of Oklahoma, providing surface weather observations across the state every five minutes?

...that a SIGMET is an advisory issued for airline crews regarding weather that may impact the safety of the aircraft, including atmospheric convection, icing conditions, or even dust storms?

...that the Antarctic Circumpolar Wave is thought by some scientists to be a very slow-moving wave in the atmosphere and ocean of the far southern hemisphere that circles the globe once every 8 years?

...that the Papagayo Jet is a strong wind that often blows across the Gulf of Papagayo west of Central America, sometimes reaching speeds as high as 30 meters per second (110 km/h; 67 mph)?

...that atmospheric optics is the study of different optical phenomena in the atmosphere, including sunsets, rainbows, and sun dogs?

...that the GME was a numerical weather prediction model run by Deutscher Wetterdienst, the German national meteorological service?

Recent and ongoing weather

This week in weather history...

November 12

1970: The Bhola cyclone drove a 20 foot (7 meter) storm surge into areas of present-day Bangladesh, killing more than 500,000 people. It was the deadliest tropical cyclone in recorded history.

November 13

1984: Hurricane Klaus dissipated in the northern Atlantic Ocean.

November 14

1969: The Saturn V rocket carrying the Apollo 12 mission into space was struck by lightning, nearly causing a mission abort.

November 15: Start of the South-West Indian Ocean cyclone season

1989: Dozens were killed in a severe weather outbreak across the eastern half of North America, mainly in the Southeastern and Northeastern United States.

2006: Hurricane Sergio, the strongest Pacific hurricane on record in the month of November, reached its peak intensity, with maximum sustained winds of 110 miles per hour (180 km/h).

November 16

2007: Cyclone Guba reached peak intensity over the Coral Sea. Flooding from the storm's rainbands eventually killed more than 140 people in Papua New Guinea.

November 17

1999: Hurricane Lenny made landfall on Saint Croix. It was an unusual storm in many ways, striking the island as the strongest Atlantic hurricane on record for the month of November, while moving in an unprecedented west-to-east direction through the Caribbean.

November 18

2017: The NOAA-20 weather satellite was launched.

Selected biography

Portrait of William Ferrel

William Ferrel (1817 – 1891) was an American meteorologist who developed theories which explained the general mid-latitude atmospheric circulation in detail, now known as the Ferrel cell in his honor. Ferrel improved upon the concept of the Hadley cell by compensating for the Coriolis effect.

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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 weather.

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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