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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Pyrocumulus clouds caused by a wildfire in Yellowstone National Park.
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Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei. Initially, a tropical storm to its northwest hindered the development and motion of Tip, though after it tracked further north Tip was able to intensify. After passing Guam, it rapidly intensified and reached peak winds of 305 km/h (190 mph) and a worldwide record low sea-level pressure of 870 mbar (hPa, 25.69 inHg) on October 12. At its peak strength, it was also the largest tropical cyclone on record with a diameter of 2,220 km (1,380 mi). It slowly weakened as it continued west-northwestward, and later turned to the northeast under the influence of an approaching trough. Tip made landfall on southern Japan on October 19, and became an extratropical cyclone shortly thereafter.
U.S. Air Force Reconnaissance flew into the typhoon for 60 missions, making Tip one of the most closely observed tropical cyclones. Rainfall from the typhoon breached a flood-retaining wall at a United States Marine Corps training camp in the Kanagawa Prefecture of Japan, leading to a fire which injured 68 and killed 13 Marines. Elsewhere in the country, the typhoon led to widespread flooding and 42 deaths, and offshore shipwrecks left 44 killed or missing.
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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...
July 1
1992: The national meteorological service of New Zealand, known as the MetService, was established as a state-owned enterprise.
2005: Severe flooding shut down almost all transportation in the Indian state of Gujarat. More than 100 people were eventually killed by the flooding.
July 2
1997: The third tornado in 51 years struck Windsor, Ontario.
July 3
1996: Tropical Storm Cristina made landfall near Puerto Ángel, the third tropical cyclone to strike southern Mexico in 10 days.
2014: Hurricane Arthur made landfall just before midnight near Beaufort, North Carolina, the first hurricane to strike the United States in almost two years.
July 4
1977: A severe windstorm, known as a derecho, struck areas of Wisconsin and Michigan.
1999: Another severe derecho produced 90 miles per hour (145 km/h) winds that downed 25 million trees in the Boundary Waters Canoe Area Wilderness of northeastern Minnesota.
July 5
1805: Robert FitzRoy, captain of the HMS Beagle and a pioneering British meteorologist, was born in Suffolk, England.
1937: The hottest temperature in Canadian history, 45.0 °C (113.0 °F), was recorded at both Midale and Yellow Grass, Saskatchewan.
July 6
2005: A tornado outbreak spawned by the outer rainbands of Hurricane Cindy began over the Southeastern United States.
July 7
2006: A major derecho raced from South Dakota to New York, killing one person and causing over $100 million in damage.
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Sakuhei Fujiwhara (藤原咲平 Fujihara Sakuhei?, October 29, 1884 – September 22, 1950) was a Japanese meteorologist who became the namesake for the Fujiwhara effect, an important interaction when forecasting cyclone tracks, particularly tropical cyclones. Novelist Jiro Nitta is his nephew and mathematician Masahiko Fujiwara is his grandnephew. He preferred to spell his surname as Fujiwhara, which is unusual by modern standards: Hepburn romanization (Fujihara or Fujiwara) is more common after World War II. Japanese texts give the furigana for his name as either Fujihara, Fujiwara or both.
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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
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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