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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In meteorology, precipitation is a term for any product of the condensation of atmospheric water vapour that is deposited on the Earth's surface. It occurs when the atmosphere, becomes saturated with water vapour and the water condenses, falling out of solution. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air. Precipitation forms via collision with other rain drops or ice crystals within a cloud.
Precipitation that reaches the surface of the earth can occur in many different forms, including rain, freezing rain, drizzle, ice needles, snow, ice pellets or sleet, graupel and hail. While snow and ice pellets require temperatures to be near or below freezing at the surface, hail can occur during much warmer temperature regimes due to the process of its formation. Precipitation also occurs on other celestial bodies—including snow on Mars and a sulfuric acid rain on Venus—though both of these evaporate before reaching the surface.
Moisture overriding associated with weather fronts is a major method of precipitation production. If enough moisture and upward motion is present, precipitation falls from convective clouds such as cumulonimbus and can organize into narrow rainbands. Precipitation can also form due to forced ascent up the windward side of a mountain or mountain range. Precipitation is a major component of the water cycle, and is responsible for depositing essentially all of the fresh water on the planet. Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year; 398,000 km3 (95,000 cu mi) of it over the oceans.
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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
- Wikinews weather portal
- April 25: Disposal of fracking wastewater poses potential environmental problems
- April 15: Wikinews Shorts: April 14, 2012
- March 30: Report indicates continued severe weather problems still looming
- March 17: Indiana teen softball player recovering after lighting strike
- March 17: Heavy rains welcomed in Texas
- 2012 Atlantic hurricane season
- 2012 Pacific typhoon season
- Tornadoes of 2012
This week in weather history...
April 22: Earth Day
2011: A nighttime tornado, caused major damage in parts of St. Louis, Missouri, including Lambert-St. Louis International Airport, but amazingly caused no deaths and few injuries.
April 23
1792: John Thomas Romney Robinson, inventor of the cup-anemometer, was born in Dublin, Ireland.
April 24
2007: Two tornadoes struck the towns of Piedras Negras, Coahuila, Mexico and Eagle Pass, Texas, United States, killing 10 people.
April 25
1994: An F4 tornado killed three people on the first day of a 3-day tornado outbreak.
April 26
1989: The deadliest tornado in world history destroyed areas of the Manikganj District, Bangladesh. More than 1300 people were killed, and over 80,000 people were left homeless.
April 27
2011: The deadliest American tornado outbreak in 76 years killed more than 300 people in the Southern United States.
April 28
2003: Santa Fe, Argentina, was struck by the worst flooding in the city's 400-year history.
Selected biography
William Ferrel (1817 – 1891) was an American meteorologist who developed theories which explained the general mid-latitude atmospheric circulation in detail, now known as the Ferrel cell in his honor. Ferrel improved upon the concept of the Hadley cell by compensating for the Coriolis effect.
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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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