Have you ever seen a cloud that appears to have rain falling from it that disappears before reaching the ground? That’s what meteorologists call virga. The word virga comes from Latin and means “twig” or “branch.” Virga forms in conditions where the air is dry, and often warm. When there’s a layer of drier, warmer air near the ground, the precipitation falling from the cloud above will evaporate before hitting Earth. Some of the places you’re more likely to see virga are in deserts, at high altitudes, in the western U.S. and Canadian prairies, the Middle East, Australia and North Africa. But virga can happen anywhere when the conditions are right.
View at EarthSky Community Photos. | Nanci McCraine captured this photo on December 13, 2023, overlooking the Ithaca and Cayuga Lake region of New York. Nanci wrote: “Evening sky lit up with an orange sunset including strange-looking clouds.” That’s virga! The precipitation falling from the clouds doesn’t reach the ground. Thanks for sharing, Nanci.
Virga on radar
Sometimes, when you’re looking at your weather app, you might see what looks like rain or snow on the radar, but nothing is falling outside. Instead, look up at the clouds and see if you can spot virga. The radar is picking up precipitation in the air which is just not reaching the ground. As weather.gov says:
The radar isn’t lying, rather, the the rain or snow is not hitting the ground. If you have a dry air mass in place in the low levels, sometimes rain cannot completely penetrate that dry layer before it evaporates.
This graphic gives you a better idea of how virga forms. The rainclouds higher up in the atmosphere are dropping rain, but as that moisture hits drier air below, it evaporates. So you might see radar indicating rain or snow, but nothing is reaching the ground. Image via weather.gov (public domain).
Do you want to learn to identify virga when you see it? Check out the photos on this page from our global EarthSky community. Once you acquaint yourself with the variations of virga, you’ll be able to spot it in your own sky. If you capture a photo of virga, submit it to us!
Photos of virga from EarthSky’s community
View at EarthSky Community Photos. | Jennifer Browne captured this scene of virga and New Mexico’s Sangre de Cristo Mountains on October 23, 2023. Jennifer wrote: “Looking west from my home. The magic of Santa Fe sunsets.” Thank you, Jennifer! Look closely, and you’ll see the wispy undersides of the clouds. That’s virga.View at EarthSky Community Photos. | Sandi Hryhor in Blairstown, New Jersey, caught this image of virga on March 26, 2022. Sandi wrote: “Taken at the Blairstown airport. It was completely overcast when we left our house 10 miles away, then some sun, then it hailed, and this sky greeted us when we arrived.” Thank you for sharing!View at EarthSky Community Photos. | Mike Lewinski captured this view near Tres Piedras, New Mexico. Mike wrote: “Venus and the waning crescent moon at dawn on June 1, 2019, over the Sangre de Cristo mountains near Taos. There is virga near the horizon, extending downward from the clouds.” Thanks, Mike!
More photos
Virga over West Texas. Image via EarthSky founder, Deborah Byrd.View at EarthSky Community Photos. | Peter Lowenstein captured this scene from Mutare, Zimbabwe, on March 5, 2019. He wrote: “Some lingering clouds and a strange curtain of virga left over after a late afternoon shower produced a spectacular display just after the sun had set below the horizon.” Thank you, Peter!View at EarthSky Community Photos. | Here’s a tricky one: a virga rainbow. Hazel Holby in Willows, California, captured this image on September 29, 2021. She wrote: “Can you tell me how this rainbow managed to form? Thank you and love your site!” Thank you, Hazel! Les Cowley of the website Atmospheric Optics said: “This is a broad bow and also of variable width. These suggest that it was made by virga or other small water droplets. The smaller the water drops, the broader the bow. When the drops get down to mist size, then we have a fogbow.” Thank you, Les!
Bottom line: Learn what virga is and how it forms, and see great photos to help you learn how to identify it yourself!
0 Commentaires