The other day I was flying from Eureka, NV to Yerington, NV. It was early afternoon and there were some cumulous clouds building fairly rapidly to the south and west.

At Austin I had to turn south, which was going to take me under some of those towering clouds. Flight watch said there was no thunderstorm activity in my area, though there would be later on. I was already hitting 1000 to 1500 fmp up and down drafts.

I turned south, and after a couple minutes saw a massive dry lake bed about 15 miles ahead of me. What caught my attention was that virga was falling out of the cloud above the lake, while at the same time huge towers of dust were coming up off the lake bed. The virga and the dust towers met at about 5000 feet agl, looking a lot like a set of light and dark teeth coming together.

With a limited fuel supply and a lot of restricted airspace between me and an alternate airport I was hesitant to divert, but after watching this for a minute I decided that whatever was going on, it wasn't good. I diverted to Lovelock, and two hours later while crossing the Sierra's I looked to the south east and saw a thunderstorm in the Yerington/Tahoe area that had to be 60 miles across.

I'm still confused on how you get virga falling out of a cloud while dust towers are lifting up into the cloud. Anybody know what's going on here?

Im not going on there. You were wise to divert.

Tim

I'm no meteorologist, but wherever there is air moving down (i.e. below the virga) there is air moving up to replace it (i.e. the dust being lifted off of the lake bed).

Virga is always bad news because it can cause very nasty down-drafts and sometimes even a microburst. The air within the virga is giving up latent heat to evaporate the rain water, therefore, cooling the air. This column of cold air, within and below the virga, is heavier than the air around it and ultimately begins sinking toward the ground. Given enough energy exchange, a downdraft will develop. When this downdraft air strikes the ground it then moves laterally and picks up dust. To complete the cycle, this dusty air then disperses and mixes with upward moving warm air. That may or may not be what caused the phenomenon you saw, but it's my guess.

Good decision on the divert.

-Matt