Derecho explained: What is it? How does it form?

What is a derecho?

A derecho is a fast moving, long-lived storm that known for intense straight-line winds. In order to be classified as a derecho, the storm complex must travel a distance of 240 miles with damaging winds greater than 58 mph for most of the storm’s path.

Often times, a derecho can produce straight line winds in excess of 100 mph.

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Typically, a derecho forms from a cluster of thunderstorms that organize into a bow shaped complex known as a bow echo. When the storms are guided by strong, unidirectional, winds and forced into warm and humid air, the storm rapidly intensifies.

This happens because the leading edge of the storm, known as the gust front, drives rain cooled air under the preceding warm air. This results in rapid thunderstorm development as the warm, moist air rises into the complex.

The creation of these new thunderstorms reinforces the rain cooled downdrafts which then result in further intensification in straight-line winds. This process continues until the storm moves into an area lacking warmth or moisture.