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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...)

Selected article

The Great Lakes Storm of 1913 was a blizzard which produced hurricane-force winds that devastated the Great Lakes basin in the United States Midwest and the Canadian province of Ontario from November 7, 1913, to November 10, 1913.

The deadliest and most destructive natural disaster to ever hit the lakes, the storm killed over 250 people, destroyed 19 ships, and stranded 19 others. It produced 6-foot drifts of snow in the surrounding land areas, snapped power poles, and paralyzed many areas for days, especially the area around Cleveland, Ohio.

The financial loss in water-bound vessels alone was nearly $5 million, or about $100 million in present-day adjusted dollars. The large loss of cargo, including coal, iron ore, and grain, meant short-term rising prices for consumer products throughout North America.

Recently selected articles: Extratropical cyclone, Ice Storm of 1998, More...

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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.

Previously selected pictures: Ground fog, Noctilucent cloud, Elie, Manitoba tornado, More...

More did you know...


...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?


Recent and ongoing weather

This week in weather history...

June 17

1946: One of the deadliest tornadoes in Canadian history struck Windsor, Ontario, killing 17 people.

June 18

1993: Météo-France, the national meteorological institution for France, was founded.

June 19

1962: The TIROS-5 weather satellite was launched from Cape Canaveral Air Force Station, Florida. The TIROS-7 satellite from the same program was launched exactly one year later.

June 20

1957: An extremely damaging F5 tornado killed 11 people in Fargo, North Dakota.

June 21

2004: Typhoon Dianmu made landfall on Honshu, Japan, killing 4 people. Another 2 were killed in South Korea.

June 22

1972: Hurricane Agnes made landfall as a strong tropical storm near New York City. It would cause devastating flooding inland, killing 113 people and causing more than $2 billion in damage (1972 USD).

June 23

1944: An unusual long-lived tornado tracked through mountainous West Virginia, killing 100 people.

Selected biography

Edward Norton Lorenz (May 23, 1917 – April 16, 2008) was an American mathematician and meteorologist who established the theoretical basis of weather and climate predictability, as well as the basis for computer-aided atmospheric physics and meteorology. He is best known as the founder of modern chaos theory, a branch of mathematics focusing on the behavior of dynamical systems that are highly sensitive to initial conditions.

His discovery of deterministic chaos "profoundly influenced a wide range of basic sciences and brought about one of the most dramatic changes in mankind's view of nature since Sir Isaac Newton," according to the committee that awarded him the 1991 Kyoto Prize for basic sciences in the field of earth and planetary sciences. (Full article...)

Previously selected biographies: Vilhelm Friman Koren Bjerknes; Anders Celsius, More...

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WikiProjects

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.

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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