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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Ground fog is a type of fog formed by the ground cooling a warm layer of air near the surface to its dew point. This scene is in East Frisia, Germany just after sunrise.
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A surface weather analysis is a type of weather map which provides a view of weather elements at a specified time based on information from ground-based weather stations. Weather maps are created by plotting or tracing the values of relevant quantities such as sea level pressure, temperature, and cloud cover onto a geographical map to help find synoptic scale features such as weather fronts.
The first weather maps in the 19th century were drawn well after the fact to help devise a theory on storm systems. After the advent of the telegraph, simultaneous observations of weather became possible for the first time, and beginning in the late 1840s, the Smithsonian Institution became the first organization to draw real-time surface analyses. Use of surface analyses began first in the United States, spreading worldwide during the 1870s. Use of the Norwegian cyclone model for frontal analysis began in the late 1910s across Europe, with its use finally spreading to the United States during World War II.
Surface weather analyses have special symbols which show frontal systems, cloud cover, precipitation, or other important information. For example, an H may represent high pressure, implying good and fair weather. An L on the other hand may represent low pressure, which frequently accompanies precipitation. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, but also to depict the present weather at various locations on the weather map. The surface weather analysis is useful for visualizing general trends in the weather across a relatively large geographic area.
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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...
May 14
2007: Cyclone Akash made landfall in Bangladesh, causing almost $1 billion in damage.
May 15: Start of the East Pacific hurricane season and end of the Mauritius and Seychelles cyclone season
1896: The first tornado of a deadly sequence of tornado outbreaks killed 73 people in North-Central Texas.
May 16
1986: Severe flooding from an ice jam completely destroyed the town of Winisk, Ontario, which was subsequently abandoned. Two people were killed.
May 17
1896: A tornado outbreak killed dozens in Kansas and Nebraska.
May 18
1902: A tornado killed 114 in Goliad, Texas.
May 19
1780: An unusual darkness, lasting from noon until after sunset, fell over parts of New England.
May 20
1916: A tornado struck the town of Codell, Kansas. Incredibly, the same town would be hit by two more tornadoes on May 20, 1917 and May 20, 1918.
Selected biography
Vilhelm Friman Koren Bjerknes (March 14, 1862 – April 9, 1951) was a Norwegian physicist and meteorologist who did much to found the modern practice of weather forecasting. In 1895, he became professor of applied mechanics and mathematical physics at the University of Stockholm where he elucidated the fundamental interaction between fluid dynamics and thermodynamics. His major contribution was the primitive equations which are used in climate models. His son, Jacob Bjerknes, would introduce the ideas of weather fronts and the life cycle of extratropical cyclones, some of the most important advances in the history of meteorology.
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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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