precursor front

precursor front

An air pressure wave which moves ahead of the main blast wave for some distance as a result of a nuclear explosion of appropriate yield and low burst height over a heat-absorbing (or dusty) surface. The pressure at the precursor front increases more gradually than in a true (or ideal) shock wave, so that the behavior in the precursor region is said to be non-ideal.
Dictionary of Military and Associated Terms. US Department of Defense 2005.