We might have all seen it before at one point, when driving along an interstate that crosses an area of plain, open moor, water, or farmland. That vast expanse of land, one where trees disappear and it opens up the sky for your road trips viewing pleasure. Usually when crossing this open canvas, you may occasionally see a rain filled cloud or thunderhead that seems to look like it has a curtain or shroud looming underneath it, indicating the release of rain to the ground below. But have you ever seen this curtain of rain not quite hitting the ground? Amazing enough, this type of phenomenon that you would witness has a very interesting name. To meteorologists; it’s known as “Virga”.
Virga is a Latin word for “twig” or “branch”. It’s most likely named to this type of precipitation because of its long thin-like arms that reach down underneath a cloud. Sometimes these clouds are referred to as the” jellyfish of the sky” as the virga under them resembles tentacles of a jellyfish. No matter how virga is witnessed, it gives to a very dramatic scene with its wispy appearance.
The reason why this curtain of precipitation never reaches the ground is because it evaporates. This occurs when precipitation falls from a cloud into a dry layer of air. This layer of air tends to have very low humidity and high temperatures. As precipitation falls from the cloud, it absorbs the energy from the higher temperatures and either evaporates (if water droplets) or directly changes from a solid to a gas, called sublimation (for ice crystals). This type of phenomenon is mostly seen in dry desert and steppe climates that are prone to dry weather, high temperatures, and low humidity. Another interesting fact about the process of virga: during evaporation and sublimation, the water vapors being released into the air actually increase the relative humidity. If there is enough precipitation in the cloud, as it falls, it continues to evaporate and release moisture into the air. Soon the air becomes moist enough for precipitation to reach further down into the layer of dry air and eventually hit the ground.
Virga is certainly a dramatic sight if you ever come around to seeing it in action. It also has a very intriguing name which puts it on the list of fascinating meteorology terms. Up next, you will learn about some fascinating meteorology terms for wind.
To continue learning about Meteorology, be sure to click here.
© 2019 Meteorologist Alex Maynard