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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Lightning strikes in the outskirts of Oradea, Romania, during a thunderstorm on August 17, 2005. This storm system went on to cause major flash floods over Southern Romania.
Recently selected pictures: Snow-swept trees, Low pressure
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Global warming is the increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.
The global average air temperature near the Earth's surface rose 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 year period ending in 2005. The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations" via the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward. These basic conclusions have been endorsed by at least 30 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. While individual scientists have voiced disagreement with the conclusions of the IPCC, the overwhelming majority of scientists working on climate change are in agreement with the conclusions.
Climate model projections summarized by the IPCC indicate that average global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st century. The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a thousand years even if greenhouse gas levels are stabilized. The delay in reaching equilibrium is a result of the large heat capacity of the oceans.
Increasing global temperature will cause sea level to rise, and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation. Other effects of global warming include changes in agricultural yields, trade routes, glacier retreat, species extinctions and increases in the ranges of disease vectors.
Remaining scientific uncertainties include the amount of warming expected in the future, and how warming and related changes will vary from region to region around the globe. There is ongoing political and public debate worldwide regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences. Most national governments have signed and ratified the Kyoto Protocol, aimed at reducing greenhouse gas emissions and outside of the United States there is considerably less debate over the effects and uncertainties of global warming.
Recently selected articles: 1999 Sydney hailstorm, Surface weather analysis, 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
- Wikinews weather portal
- February 8: European cold spell kills hundreds
- January 27: Report indicates Texas state parks still suffering following worst drought on record
- September 7: Drought conditions and high winds lead to wildfires in Texas
- August 29: Freshwater lakes in Texas show signs of extreme drought
- August 28: Tropical Storm Irene passes over New York
- 2012 Atlantic hurricane season
- 2012 Pacific typhoon season
- Tornadoes of 2012
This week in weather history...
February 5: National Weatherperson's Day
2008: The Super Tuesday tornado outbreak, the deadliest outbreak in the United States since 1985, produced 87 tornadoes which killed 57 people.
February 6
1978: The Blizzard of '78, the worst storm in the area since 1888 and the second large blizzard in as many weeks to hit the eastern United States, began dropping several feet of snow on the Northeastern United States.
1996: Heavy rain and warm temperatures started several days of significant flooding in the Pacific Northwest, resulting in more than $500 million in damage.
February 7
2002: The South Valley Surprise struck the Pacific Northwest with no warning due to the rapid deepening of the storm, causing major tree damage across the area. Portal:Weather/On this day list/February 8
February 9
1870: The National Weather Service was founded through a joint congressional resolution signed by President Ulysses S. Grant.
February 10
1972: A week-long blizzard came to an end in the country of Iran, leaving around 4,000 people dead.
1994: Cyclone Hollanda struck the island of Mauritius in the Indian Ocean, causing major damage and killing three people.
February 11
1895: The lowest temperature in the United Kingdom, -27.2°C (-16.7°F), was measured at Braemar, Grampian.
1899: During an historic cold snap that affected much of the southern United States, the state of Florida sank to −2 °F (−19 °C); its coldest temperature on record.
Selected biography
Anders Celsius (November 27, 1701 – April 25, 1744) was a Swedish astronomer who is best known for his pursuit to develop a standardized temperature scale. He determined that the melting point and boiling point of water are constant regardless of latitude, and the boiling point of water is dependant on elevation.
In 1742 he proposed a temperature scale which now bears his name, the Celsius scale, which is used worldwide for meteorological observations around the world. In his scale, the boiling point of water was 0 degrees and the freezing point was 100, while the modern Celsius scale is the reverse of this. In addition to his temperature work, he was an avid observer of the aurora borealis and participated in an expedition to measure an arc of the meridian in northern Sweden.
Recently selected biographies: Robert FitzRoy, More...
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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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