Q&A: Virga

Question: During this last round of rain I heard the weatherman talking about something called “virga.” He said it was rain that doesn’t reach the ground. So then where does that rain go? I’m confused. — DM, Phoenix, AZ

Answer: Virga is indeed rain that never makes it to the ground. It’s quite common here in the desert southwest. I shot the above photo of some virga right after sunset a couple rains ago.

All it takes to get virga is a layer of warm dry air underneath the rain cloud. And we have plenty of warm dry air around these parts. If the rain isn’t too heavy, and if the air it falls through is warm and dry enough, the rain simply re-evaporates before it hits the ground.

This can also happen with snow, but the temperature differences involved make that a less common event. You asked what happens to all that H2O after it re-evaporates. You are correct that it has to go somewhere. What happens is, it returns to the sky as invisible water vapor, and rejoins the natural hydrologic cycle. Sooner or later it becomes yet another cloud. Eventually, it will make it all the way to the ground (or ocean).

If you’ve ever been outside in one of those “light rains” where the drops are more “blowing around in a mist” than actually soaking the ground, you’ve been “virgaed,” if you’ll permit me to coin a term. The exact altitude at which re-evaporation occurs is a variable. It can be very close to ground level, but is usually several hundred feet.

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