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 · Disasters · Water
Selected picture
Different types of snowflakes are shown in this series of photos, taken by Wilson Bentley in 1902. The phrase "no two snowflakes are alike" is mostly based in truth, as their shape, size, and branching features are highly sensitive to the exact humidity, temperature, and other atmospheric conditions in which they form.
Recently selected pictures: Ground fog, Virga over London, Hurricane Isabel satellite, More...
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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.
Recently selected articles: Great Lakes Storm, Extratropical cyclone, More...
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 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...
April 19
2008: Typhoon Neoguri made landfall in Guangdong province of southern China, the earliest tropical cyclone to strike the nation in recorded history.
April 20
2004: A strong tornado, part of a surprise outbreak of 29 tornadoes, killed 9 people in Utica, Illinois.
April 21
1965: A devastating tornado outbreak killed 58 people near Chicago.
April 22: Earth Day
1992: A subtropical cyclone, the first ever recorded in the Atlantic Ocean in the month of April, reached peak intensity far south of Bermuda.
April 23
1792: John Thomas Romney Robinson, inventor of the cup-anemometer, was born in Dublin, Ireland.
April 24
1908: One of the deadliest tornadoes in US history killed at least 143 people in Louisiana and Mississippi.
April 25
1994: An F4 tornado killed three people on the first day of a 3-day tornado outbreak.
Selected biography
Vice Admiral Robert FitzRoy (July 5, 1805 – April 30, 1865) achieved lasting fame as the captain of HMS Beagle and as a pioneering meteorologist who made accurate weather forecasting a reality, also proving an able surveyor and hydrographer as well as Governor of New Zealand.
FitzRoy developed charts to allow predictions to be made using observation stations connected by telegraph to transmit to him daily reports of weather at set times. The first daily weather forecasts were published in The Times in 1860, and in the following year a system was introduced of hoisting storm warning cones at the principal ports when a gale was expected. The Weather Book which he published in 1863 was far in advance of the scientific opinion of the time.
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Weather: Meteorology | Atmosphere | Basic meteorological concepts and phenomena | Climate | Clouds | Cyclones | Floods | Precipitation| Seasons | Severe weather and convection | Snow | Storms | Tornadoes | Tropical cyclones | Weather events | Weather lore | Weather hazards | Weather modification | Weather prediction | Weather warnings and advisories| Winds
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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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