**** Info via Environment Canada
Ever heard of Virga?
Have you ever wondered why sometimes we see rain on the radar, but it is not raining? This could be caused by a weather phenomenon called virga.
Virga occurs when precipitation falls from a cloud but evaporates before reaching the ground. It typically appears as wispy streaks or bands of precipitation that hang from the cloud but do not reach the Earth’s surface.
Virga. Source: World Meteorological Organization, credit: Elisa Sala Salvador.
Virga is commonly observed in dry and arid regions where the air is too dry to allow precipitation to reach the ground. It can also occur in areas with strong winds that cause the precipitation to evaporate before it reaches the surface. It is often regarded as a precursor to impending precipitation and can provide valuable information about weather conditions in the surrounding area.
On a radar image, virga appears as a band or streak of precipitation that extends from a cloud but does not reach the ground. The radar image shows the area of precipitation, with virga appearing as a lighter shade of precipitation because it’s detected as moisture in the air. The radar image is helpful for tracking the intensity and movement of virga and other weather phenomena.
Predicting virga can be challenging since it requires a complex interplay of atmospheric conditions. However, there are certain factors that make the formation of virga more likely. These include dry air, high cloud bases, strong winds, and specific weather patterns such as high-pressure systems and dry fronts. By analyzing weather data and taking these factors into account, meteorologists can make predictions about the probability of virga in a particular area. Nonetheless, predicting virga is still challenging, and there is always some level of uncertainty involved.
