Evaporating Rainfall: What is virga and how does it form?

We dive into the science behind evaporating rainfall

Virga is essentially rain that evaporates before reaching the surface.

If you’re a regular KSAT-12 viewer, you’ve probably heard one of the meteorologists mention the word “virga” when there are returns on the radar but not much rain, if any, at the surface.

So what exactly is virga and how does it form? Let’s dive into the details below:

In a basic sense, virga occurs when raindrops fall from a cloud, but evaporate before reaching the ground.

This is often due to a pocket of dry air that sits between the surface and the base of the cloud, which causes those raindrops to evaporate as they pass through.

When virga occurs, you may still see rain on the radar since the radar beam is sampling raindrops above that dry air, but only a few sprinkles, if anything, may actually be surviving the fall to the ground.

Sometimes you can even spot virga in the sky! Trails or “wisps” of precipitation can be seen stretching out from the base of a cloud, but dissipate before reaching the surface.

So the next time you see rain on the radar right overhead but not much is actually falling in your backyard, this may be a reason why!



About the Author:

Meteorologist Mia Montgomery joined the KSAT Weather Authority Team in September 2022. As a Floresville native, Mia grew up in the San Antonio area and always knew that she wanted to return home. She previously worked as a meteorologist at KBTX in Bryan-College Station and is a fourth-generation Aggie.