Why does rain or snow not hit the ground at times?
While listening to weather reports, we often hear meteorologists say that it rained or snowed in a particular region on a particular day. However, the residents of those of those areas may disagree. Reporters also say that there was definitely some kind of precipitation, but somehow, none of us gets to see anything! Weird, right? However, this doesn’t mean that the weather reports are wrong. Even though it might have rained or snowed, the precipitation doesn’t always reach the ground. Yes, you read that right! There are times when precipitation (mostly rain) evaporates before it hits the ground. Intriguing indeed! Well, this unusual phenomenon is known by the name Virga. Here’s a low-down on this strange play of nature.
How does Virga look like?
It looks like wispy, grey-coloured streaks hanging from the base of clouds. The term Virga is directly related to this appearance. Just like most clouds derive their name from Latin terms, Virga too is derived from the Latin term ‘virga’ meaning ‘twig’ or ‘branch.’ Geologists believe that this term likely refers to the delicate twig-looking streaks that it produces. In this context, you may also find it interesting to know that Virga is also known by the alternative name ‘fall streaks’, literally meaning falling streaks.
Why does Virga occur?
You might be thinking that the reason behind Virga’s occurrence is something complicated. But guess what, it’s quite the contrary. Virga occurs when any kind of precipitation falls from high clouds, but before it can reach the ground, it is absorbed by very dry air (imagine low humidity days or places) or very high temperatures below. This is why, you’re more likely to experience Virga in desert areas, which have both high temperatures accompanied by low humidity. What follows this is something you have already read in your science and geography textbooks. The liquid raindrops or the snow crystals at first touch the warm and dry air, from where they absorb all the excess heat and before they have the chance to hit the ground, they turn into water vapour and go back up where they came from! Magic! Doesn’t this remind you of the process of sublimation that you studied; where a solid substance directly converts into its vapour state without undergoing through the intermediate liquid phase?
Detecting Virga
Yes, it is normal to assume that since Virga never touches the ground, it is not only invisible to the naked human eyes, but also really hard to detect. However, the good news is, the weather radar can very well detect Virga as it appears as shades of light green (in case of rain) and light blue (in case of snow). So, the next time, the weatherman on the news says that there was some form of precipitation, but you think you missed out on it, don’t feel deceived. It might have been just a case of Virga!