What is virga? There’s rain on radar, but it’s not raining!

The fluid dynamics associated with atmospheric disturbances cause the downstream air (ahead of the disturbance, before it arrives at a location) to rise, and the upstream air (behind the disturbance, i.e., after the disturbance has passed) to sink.  If there is sufficient moisture in the area of rising air, clouds and precipitation may form.  Necessary […]