Virga

Virgae can cause varying weather effects because as rain is changed from liquid to vapor form it removes significant amounts of heat from the air due to water's high heat of vaporization. Precipitation falling into these cooling downdrafts may eventually reach the ground. In some instances these pockets of colder air can descend rapidly, creating a wet or dry microburst which can be extremely hazardous to aviation. Conversely, precipitation evaporating at high altitude can compressionally heat as it falls, and result in a gusty downburst which may substantially and rapidly warm the surface temperature. This fairly rare phenomenon, a heat burst, also tends to be of exceedingly dry air.

Virgae also have a role in seeding storm cells. That is because small particles from one cloud are blown into neighboring supersaturated air and act as nucleation particles for the next thunderhead cloud to begin forming.

Etymology

The word is derived from the Latin virga, meaning rod, sprig, staff, branch, shoot, twig, spray, sprout, switch or graft.