Photo credit – Quasipalm – Public domain
Cloud of the Day – Virga
Virga is not really a cloud. It’s a form of precipitation. But it’s not exactly precipitation in the normal sense, either. Virga is precipitation that falls out of a cloud but doesn’t reach the ground. Can you call it rain if it doesn’t make anything wet?
Photo credit – Simon A Eugster CC-BY-SA / Bidgee CC-BY
Virga doesn’t get its name as you’d expect. It’s not because it is virgin precipitation that doesn’t consummate its existence by touching the Earth. Virga has its root in Latin for “branch” or “twig.” I suppose it does kind of look as if the cloud has sprouted branches. I guess. If you hold your mouth right. Still, I like the other, more poetical, meaning better.
Photo credit – David Kibble / David Foxx
Virga happens when there is enough moisture in the air to form a cloud, and enough to form ice crystals or water droplets that are heavy enough to fall. Then, either because the air is too dry or too warm closer to the ground, the precipitation sublimates* or evaporates on its way down. These conditions prevail in dry areas, so virga is often seen in deserts or prairies.
Yes, there is precipitation, but you won’t need your umbrella.
*phase transition from solid to gas with no liquid phase.
rjb
I saw this in Ganado Az some years back. The sun had set, pink clouds hung over the mesa and it looked like purple rain was coming down but never hit the ground… Fabulous. Coming from Florida where the rain comes at you in sheets and sometimes erases the world altogether, to see rain evaporate in mid air is magic.
Yes. You could almost write a poem about it, couldn’t you?
rjb