The additional rain reinforces the cold pool and strengthens the rear inflow of air, with the thunderstorm complex reaching a semi-steady state condition. The bowing of the gust front forces more warm moist air up, creating new thunderstorm cells, and the process repeats. Tilting the updraft allows the cumulonimbus cloud to expand further, increasing the aerial coverage of rain which, in turn, further adds to the cold pool of air under the thunderstorm and thereby strengthens the gust front, causing it to bow out. This causes the updraft to tilt toward the trailing edge. As this new cell matures, the rain it produces reinforces the 'pool' of rain-cooled air, allowing the gust front to maintain its strength.Īs the cold pool increases in size, it induces an inflow of air (orange arrow at right) on the trailing side of the thunderstorm complex. The boundary between the rain-cooled air and warm-moist air is called the gust front.Īir forced up by the gust front begins the next new thunderstorm cell formation. The cooler, more dense air hugs the surface as it spreads, forcing lighter warm-moist air up into the atmosphere. This downdraft marks the dissipation stage of that particular thunderstorm cell.

As the rain-cooled downdraft reaches the Earth's surface, it spreads horizontally.

A derecho comes from a long-lived bow echo or a series of bow echoes.īow echoes usually arise from a cluster of storms, but may also begin from just a single supercell thunderstorm. The term 'bow echo' is based on how bands of rain showers or thunderstorms 'bow out' when the storm's strong winds reach the surface and spread horizontally. National Centers for Environmental Predictionĭerechos typically are associated with bands of showers or thunderstorms that assume a curved or bowed shape.Preparedness and Mitigation: Individuals (You!).

Preparedness and Mitigation: Communities.The Positive and Negative Side of Lightning.

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