Scud clouds are low, detached clouds caught in the outflow beneath the thunderstorm. As cold air first reaches the ground, it lifts relatively warm air, resulting in saturation through ascent. Thus, the presence of sub-thunderstorm base scud clouds almost always indicates the presence of outflow.

This is a dissipating multicell anvil cloud, looking northeast, late in the afternoon near Fort Morgan, Colorado. Note the lack of precipitation beneath the dissipating storm cell, except for the white virga streak behind the tree line.

The area close to this virga could be quite dangerous for low-level aircraft operations. Microbursts that occur with virga are aptly called dry microbursts, even though a spattering of raindrops may reach the surface.

Microbursts

Terms for using data resources. CD-ROM available. Credits and Acknowledgments for WW2010. Department of Atmospheric Sciences (DAS) at the University of Illinois at Urbana-Champaign.

rain foot, dust foot