Portal:Weather
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
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Flakes of snow highly magnified by a low-temperature scanning electron microscope (SEM). The colors are called "pseudo colors"; they are computer generated and are a standard technique used with SEM images.
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Cyclone Elita was an unusual tropical cyclone that made landfall on Madagascar three times. The fifth named storm of the 2003–04 South-West Indian Ocean cyclone season, Elita developed on January 24 in the Mozambique Channel. It strengthened to become a tropical cyclone before striking northwestern Madagascar on January 28. Elita weakened to tropical depression status while crossing the island, and after exiting into the southwest Indian Ocean it turned to the west and moved ashore for a second time on January 31 in eastern Madagascar. After crossing the island, the cyclone intensified again after reaching the Mozambique Channel, and Elita turned to the southeast to make its final landfall on February 3 along southwestern Madagascar. By February 5 it had undergone extratropical transition, and the remnants of Elita moved erratically before dissipating on February 13.
Elita dropped heavy rainfall of over 200 mm (8 inches), which damaged or destroyed thousands of houses in Madagascar. Over 50,000 people were left homeless, primarily in Mahajanga and Toliara provinces. Flooding from the storm damaged or destroyed more than 450 km² (170 sq mi) of agricultural land, including important crops for food. Across the island, the cyclone caused at least 33 deaths, with its impact further compounded by Cyclone Gafilo about two months later. Elsewhere, the cyclone brought rainfall and damage to Mozambique and Malawi, while its outer circulation produced rough seas and strong winds in Seychelles, Mauritius, and Réunion.
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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 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...
August 24
1956: Severe flooding began in Mannum, South Australia, after a levee broke outside of town.
August 25
1635: A major hurricane struck southeastern New England, killing more than 46 people.
August 26
1995: As part of a hyperactive hurricane season, 5 tropical cyclones existed in the Atlantic basin simultaneously, the only time in history this has ever occurred.
August 27
1893: The Sea Islands Hurricane struck near Savannah, Georgia, the last major hurricane to do so.
August 28
1983: Hurricane Barry made landfall about 35 miles (56 km) south of the Texas border, in the Mexican state of Tamaulipas. Hundreds of homes were destroyed, but no one was killed.
August 29
2005: Hurricane Katrina pushed an incredible storm surge onshore in Louisiana, Mississippi, and Alabama, killing almost 2,000 people and causing more than $80 billion in damage. It was the costliest Atlantic hurricane in history, as well as the deadliest in the United States since the 1928 Okeechobee Hurricane.
August 30
1878: A record flood killed almost 400 people in and around Miskolc, Hungary.
Selected biography
John Park Finley (April 11, 1854 – November 24, 1943) was an American meteorologist and Army Signal Service officer who was the first person to study tornadoes intensively. He wrote the first known scientific book on the subject of tornadoes, as well as many other manuals and booklets. He was responsible for the first national network for reporting tornado touchdowns and outbreaks, and kept an archive of tornado reports from across the United States. He also collected vast climatological data, set up a nationwide weather observer network, started one of the first private weather enterprises, and opened an early aviation weather school.
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Categories
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
Wikiprojects
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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