The weather portal

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.

Related portals: Earth sciences ( Atmosphere  · Atmospheric Sciences)  · Tropical cyclones Featured article  · Disasters  · Water

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Lightning strike jan 2007.jpg

A bolt of lightning struck just behind this hill, near Swifts Creek, Victoria, Australia. Lightning kills more people than any other thunderstorm phenomenon (including tornadoes), and strikes approximately 100 times per second across the world.

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Snow events are a rarity in the U.S. state of Florida, as freezing temperatures in the state are generally caused by the cold and dry winds of anticyclones. Most of the state is in a rare portion of the continental United States which receives a mean maximum monthly snowfall amount of zero, the only other such areas being southern Texas and California. However, snow does occur, especially in the northern interior sections of the state, sometimes more than once in a season. Areas near Jacksonville have seen several inches of snow on occasion, and snow flurries have been reported as far south as Homestead. Generally, for snow to occur, the polar jet stream must move southward through Texas and into the Gulf of Mexico, with a stalled cold front across the southern portion of the state curving northeastward to combine freezing air into the frontal clouds.

Snowfall events by month in Florida

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Did you know...

...that Hurricane Debbie is the only known tropical cyclone ever to strike Ireland?

...that the Tempest Prognosticator, one of the earliest attempts at a weather prediction device, employed live leeches in its operation?

...that eyewall replacement cycles are among the biggest challenges in forecasting tropical cyclone intensity?

...that the Braer Storm of January 1993 is likely the strongest extratropical cyclone ever recorded in the north Atlantic Ocean?

...that in medieval lore, Tempestarii are magicians with the power to control the weather?

...that the omega equation is essential to numerical weather prediction?

Recent and ongoing weather

This week in weather history...

January 20

1910: The Seine river overflowed its banks, marking the beginning of the Great Flood of Paris.

2005: A two day storm began that would drop 1–3 feet (30–90 cm) of snow over parts of New England.

January 21

1918: The Mackay cyclone leveled the city of Mackay, Queensland.

2009: In the early morning, Cyclone Fanele struck the east coast of Madagascar, killing 10 people.

January 22

1999: One person was killed in Tennessee in the final day of a six-day tornado outbreak sequence.

2016: A major blizzard began to affect the Mid-Atlantic states, ultimately resulting in all-time record snowfalls for a large portion of the United States.

January 23

1971: The temperature dropped to −80 °F (−62 °C) in Prospect Creek, Alaska, the coldest temperature ever recorded in the United States.

January 24

1967: A rare winter tornado outbreak affected the area around Saint Louis, Missouri, killing 3 people. The next day, thunderstorms produced sleet, freezing rain, and snow in the same areas.

2009: European windstorm Klaus made landfall near Bordeaux, France, with wind gusts of up to 200 kilometers per hour (120 mph).

January 25

1990: A European windstorm known as the Burns' Day storm killed almost 100 people, mainly in the United Kingdom.

2008: The first in a series of winter storms impacted China, beginning what would be China's most severe winter in half a century.

2009: An avalanche killed 10 hikers in Gümüşhane Province, Turkey.

January 26

1978: The Great Blizzard of 1978 struck the Great Lakes and Ohio Valley with several feet of snow and winds gusting to 100 mph. Seventy people died in the storm.

Selected biography

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.

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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.

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