Outflow boundary

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For information on the book Gust Front by author John Ringo, see Legacy of the Aldenata

Outflow boundary on radar.

An outflow boundary is a storm-scale or mesoscale boundary separating thunderstorm-cooled air (outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature. Outflow boundaries may persist for 24 hours or more after the thunderstorms that generated them dissipate, and may travel hundreds of miles from their area of origin. New thunderstorms often develop along outflow boundaries, especially near the point of intersection with another boundary (cold front, dry line, another outflow boundary, etc.; see triple point).

Thunderstorm with lead gust front

A gust front is an outflow boundary that is the leading edge of gusty surface winds from thunderstorm downdrafts; sometimes associated with a shelf cloud or roll cloud. A wrapping gust front is a front that wraps around the mesocyclone, cutting off the inflow of warm moist air and resulting in occlusion.

Sometimes a gust front can be seen on weather radar, showing as a thin circular line of light rain pushing out from a collapsing storm. This cool outdraft can then energize other storms which it hits by assisting in updrafts. Gust fronts colliding from two storms can even create new storms.