Conventionally, virga is known as rain that dries up as it falls, beyond the density needed to be
visible. They can also be falling ice crystals at high altitudes where temperatures are easily as cold
as -12f at 20,000 feet, which are about the altitudes of these clouds. The falling of the crystal gives
it a tail-like appearance under the cloud.
All that is required for virga to form are enough water molecules to gather in one spot of a cloud that
they fall from the effects of their own density. The molecules disperse and are no longer seen as they
fall since the rest of the huge sky is relatively dry. Virga is a less common cloud, but not rare
outside the driest deserts, where even there the jet stream may bring them overhead any time of year.