Anyone who lives in an arid or semiarid environment is familiar with virga, precipitation that evaporates in dry air before reaching the ground. Viewed from a distance, it resembles a curtain, hanging from the bottom of a rain or storm cloud but not extending down to the terrain below.
During our current drought along the Front Range, many of us check the local radar when rain is expected. Watching the green or yellow blobs move toward and then over our neighborhood, we anticipate a downpour. In many cases, however, we stay dry or receive only a light drizzle, a victim of virga.
This phenomenon is enhanced in Metro Denver when storms arrive from the south or west. As the air descends from higher terrain, it warms up and dries out and precipitation evaporates as it falls into the lower, drier layer of the atmosphere.
