Astonishing images of the moment apocalyptic 'derecho' superstorm battered New York

[Uncle Joe]

46. Here you go.

http://en.wikipedia.org/wiki/Derecho

This image shows derecho frequency for the lower 48 United States



Derecho

A derecho ( /dəˈreɪtʃoʊ/; Spanish pronunciation: [deˈɾetʃo]; deh-REH-cho) is a widespread, long-lived, straight-line windstorm that is associated with a fast-moving band of severe thunderstorms. Generally, derechos are convection-induced and take on a bow echo form of squall line, forming in an area of wind divergence in the upper levels of the troposphere, within a region of low-level warm air advection and rich low-level moisture. They travel quickly in the direction of movement of their associated storms, similar to an outflow boundary (gust front), except that the wind is sustained and increases in strength behind the front, generally exceeding hurricane-force. A warm-weather phenomenon, derechos occur mostly in summer, especially during June and July in the Northern Hemisphere, within areas of moderately strong instability and moderately strong vertical wind shear. They may occur at any time of the year and occur as frequently at night as during the daylight hours.

Derecho comes from the Spanish word for "straight" (cf. "direct&quot in contrast with a tornado which is a "twisted" wind.[1] The word was first used in the American Meteorological Journal in 1888 by Gustavus Detlef Hinrichs in a paper describing the phenomenon and based on a significant derecho event that crossed Iowa on 31 July 1877.[2]

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Winds in a derecho can be enhanced by downburst clusters embedded inside the storm. These straight-line winds may exceed 100 mph (160 km/h) (in some cases, sustained wind) in these clusters and straight-line wind gusts of up to 200 mph (320 km/h) are possible in the most extreme cases.[citation needed] Tornadoes sometimes form within derecho events, although such events are often difficult to confirm due to the additional damage caused by straight-line winds in the immediate area.

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Unlike other thunderstorms, which typically can be heard in the distance when approaching, a derecho seems to strike suddenly. Within minutes, extremely high winds can arise, strong enough to knock over highway signs and topple large trees. These winds are accompanied by spraying rain and frequent lightning from all directions. It is dangerous to drive under these conditions, especially at night, because of blowing debris and obstructed roadways. A derecho moves through quickly, but can do much damage in a short time.

There is more on the link.