Squall

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For the Final Fantasy VIII protagonist, see Squall Leonhart.

A squall is a sudden, sharp increase in wind speed which usually is associated with active weather, such as rain showers, thunderstorms, or heavy snow.[1] Squalls refer to an increase in the sustained winds over a short time interval, as there may be higher gusts during a squall event.[2] They usually occur in a region of strong mid-level height falls, or mid-level tropospheric cooling, which force strong localized upward motions at the leading edge of the region of cooling, which then enhances local downward motions just in its wake.

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[edit] Origin of the term

The word appears to be Nordic in origin, but its etymology is considered obscure. It is probably an alteration of the word squeal.[3] The first known use of the term on surface weather analyses was in the United States in the late Nineteenth Century on U. S. Signal Corp Maps, begun in 1871.

[edit] Wind

The term "squall" is universally used to refer to a sudden wind-speed increase, both historically and in the present day. To be called a squall in the United States, the wind must increase at least 18 miles per hour (8 meters per second) and must attain a top speed of at least 25 miles per hour (11 meters per second), lasting at least a full minute in duration. In Australia, a squall is defined to last for several minutes before the wind returns to the long term mean value. In either case, a squall is defined to last about half as long as the definition of sustained wind in its respective country. Usually, this sudden violent wind is often associated with briefly heavy precipitation.

[edit] Argentina

Known locally as pamperos, they are used to describe strong downsloped winds that move across the pampas, eventually making it to the Atlantic Ocean.[4]

[edit] Central America

Offshore Central America, the term gully squall is used to describe strong increases of the wind forced through sharp mountain valleys on the Pacific Ocean side of the isthmus.

[edit] Cuba

Bayamo is a term used to describe squalls emanating from tropical thunderstorms near the Bight of Bayamo.[5]

[edit] Pacific Northwest - United States

In the Pacific Northwest, a squall is a short but furious rainstorm with strong winds, often small in area and moving at high speed, especially as a maritime term.

[edit] South Africa

Bull's Eye Squall is a term used offshore South Africa, describing a squall forming in fair weather. It is named for the appearance of the small isolated cloud marking the top of the squall.[6]

[edit] Southeast Asia

Barat is a term for a northwest squall in Manado Bay in Sulawesi.[6]

[edit] Severe Weather

A shelf cloud such as this one can be a sign that a squall is imminent
A shelf cloud such as this one can be a sign that a squall is imminent

A squall line is an organized line of thunderstorms. It is classified as a multi-cell cluster, meaning a thunderstorm complex comprising many individual updrafts. They are also called multi-cell lines. Squalls are sometimes associated with hurricanes or other cyclones, but they can also occur independently. Most commonly, independent squalls occur along front lines, and may contain heavy precipitation, hail, frequent lightning, dangerous straight line winds, and possibly funnel clouds, tornadoes and waterspouts.[7] Squall lines require significant low-level warmth and humidity, a nearby frontal zone, and vertical wind shear from an angle behind the frontal boundary.[8] The strong winds at the surface are usually a reflection of dry air intruding into the line of storms, which when saturated, falls quickly to ground level due to its much higher density before it spreads out downwind.[9] In England, a squall associated with tempestuous weather is known as a blunk. Significant squall lines with multiple bow echoes are known as derechos.[10]

[edit] Signs in the sky

Shelf clouds and roll clouds are usually seen above the leading edge of a squall, also known as a thunderstorm's gust front.[11] From the time these low cloud features appear in the sky, one can expect a sudden increase in the wind in less than 15 minutes.

[edit] Winter Weather

Snow squalls can be spawned by an intrusion of cold air aloft over a relatively warm surface layer. Lake effect snows can be in the form of a snow squall. In Scotland, snow squalls are known as bluffarts.

[edit] Effects on inland lakes

A seiche is used to define the sloshing of water within a large inland lake, normally induced by a squall line.[12]

[edit] Literary Usage

Squall is a vocabulary word in the book Sarah Plain and Tall It is also used in the title of the book "White Squall", written by John Conroy Hutcheson in 1900.[13]

[edit] See also

[edit] References

  1. ^ The Weather Channel. Weather Glossary: S. Retrieved on 2006-11-19.
  2. ^ Australian Bureau of Meteorology. Weather Words. Retrieved on 2006-11-19.
  3. ^ Georoots News. Georoots News V.1#5: Changes in the Wind. Retrieved on 2006-12-30.
  4. ^ Oxford English Dictionary. Oxford University Press. 10Rev Ed edition (7 April 2005)
  5. ^ WGN-TV. Weather Words - B. Retrieved on 2006-11-19.
  6. ^ a b Golden Gate Weather Services. Names of Winds.
  7. ^ Weatherquestions.com. What is a Squall Line? Retrieved on 2006-11-19.
  8. ^ Wilfried Jacobs. EUMeTrain: Case Study on Squall Line. Retrieved on 2006-11-19.
  9. ^ Thinkquest. Meteorology Online: Squall. Retrieved on 2006-11-19.
  10. ^ Robert H. Johns and Jeffry S. Evans. Storm Prediction Center. Derecho Facts. Retrieved on 2006-11-19.
  11. ^ National Weather Service Forecast Office, Springfield, Missouri. Storm Spotter Online Training. Retrieved on 2006-11-19.
  12. ^ Lawrence A. Hughes. U. S. Weather Bureau Office, Chicago, Illinois. The Prediction of Surges in the Southern Basin of Lake Michigan. Retrieved on 2006-11-19.
  13. ^ Athelstane E-Books. John Conroy Hutcheson. Retrieved on 2006-11-19.
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