Weather is an all-encompassing term used to describe all of the many and varied phenomena that occur in the atmosphere of a planet at a given time. The term usually refers to the activity of these phenomena over short periods of hours or days, as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of time. When used without qualification, "weather" is understood to be the weather of Earth.
Weather most often results from temperature differences from one place to another, caused by the Sun heating areas near the equator more than the poles, or by different areas of the Earth absorbing varying amounts of heat, due to differences in albedo, moisture, and cloud cover. Surface temperature differences in turn cause pressure differences. A hot surface heats the air above it and the air expands, lowering the air pressure. The resulting pressure gradient accelerates the air from high to low pressure, creating wind, and Earth's rotation causes curvature of the flow via the Coriolis effect. These simple systems can interact, producing more complex systems, and thus other weather phenomena.
The strong temperature contrast between polar and tropical air gives rise to the jet stream. Most weather phenomena in the mid-latitudes are caused by instabilities of the jet stream flow (see baroclinity) or by weather fronts. Weather systems in the tropics are caused by different processes, such as monsoons or organized thunderstorm systems.
Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. In June the Northern Hemisphere is tilted towards the sun, while in December it is tilted away, causing yearly changes in the weather known as seasons. In the mid-latitudes, winter weather often includes snow and sleet, while in both the mid-latitudes and most of the tropics, tropical cyclones form in the summer and autumn. Almost all weather phenomena can occur year-round on different parts of the planet, including snow, rain, lightning, and, more rarely, hail and tornadoes.
A cumulonimbus cloud near Swifts Creek, Victoria, Australia. Cumulonimbus are so named because they combine the characteristics of cumulus clouds (puffy in nature) and nimbus clouds (causing precipitation). They are typically around 30,000-50,000 ft (10,000-15,000 m) in height, and commonly produce precipitation and lightning. Cumulonimbus clouds occasionally become severe thunderstorms, and, if rotation is present in the atmosphere, can become supercells, producing high winds, heavy rain, hail, and rarely tornadoes. Fortunately, this only happens in a small fraction of cases; most cumulonimbus produce innocuous showers or thundershowers.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)...
...that the Tempest Prognosticator, one of the earliest attempts at a weather prediction device, employed live leeches in its operation?
...that in medieval lore, Tempestarii are magicians with the power to control the weather?
- Wikinews weather portal
- May 4: Six dead following flash flooding in Palestine, Texas
- May 2: 60 people still missing after Kenyan house collapse
- December 2: Investigators blame pilot error for AirAsia crash into Java Sea
- October 19: Typhoon Koppu makes landfall in the Philippines, displacing at least 16,000
- September 11: Typhoon Etau causes more leakage at Fukushima
- 2019 Atlantic hurricane season
- 2019 Pacific typhoon season
- Tornadoes of 2019
March 23: World Meteorological Day
Edward Norton Lorenz (May 23, 1917 – April 16, 2008) was an American mathematician and meteorologist, and a pioneer of chaos theory. He discovered the strange attractor notion and coined the term butterfly effect. Lorenz was born in West Hartford, Connecticut. He studied mathematics at both Dartmouth College in New Hampshire and Harvard University in Cambridge, Massachusetts. During World War II, he served as a weather forecaster for the United States Army Air Corps. After his return from the war, he decided to study meteorology. Lorenz earned two degrees in the area from the Massachusetts Institute of Technology where he later was a professor for many years.
- Mid-October 2007 tornado outbreak
- Typhoon Meranti (2004)
- Tropical Storm Arlene (2005)
- Tropical Storm Doria (1971)
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