Have you ever checked the radar and it is showing that it is raining or snowing, but you step outside and notice there’s nothing actually falling to the ground? The radar is not making it up, as the radar is detecting precipitation falling from the clouds, it is just evaporating before it makes it to the surface. This is known as virga.
Virga occurs when precipitation falls from the clouds and encounters a layer of dry air closer to the surface. This dry air will cause rain or snow to evaporate as it falls from the cloud to the ground through this dry layer. The smaller the raindrops or snowflakes, the easier it will be for the precipitation to evaporate through the drier air. So why does it show up on radar? The radar is scanning higher up in elevation in the atmosphere at a level above that dry air layer.
Virga can be common during the winter and on hot, summer days when an active weather pattern is in place to generate precipitation, but very low relative humidity values are found closer to the surface. These setups can create beautiful views and photo opportunities especially when backlit by the sun.