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 with radial velocity and frontal boundary drawn in.

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.

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. This is sometimes the case during the event of a collapsing storm, in which the wind literally "rips it apart"

Sometimes a gust front can be seen on weather radar, showing as a thin arc or line of weak radar echos pushing out from a collapsing storm. In most cases, these echoes represent insects that have been caught in the colliding winds at the front. Occasionally, winds caused by the gust front are so high in velocity, that they may also show up on radar. 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. However, there is usually no rain accompanying the shifting winds.