fallstreaks

Fallstreaks, also known as precipitation streaks or virga, are streaks of precipitation that fall from a cloud but evaporate before reaching the ground. They are a common meteorological phenomenon observed in various cloud types, particularly in arid or semi-arid regions. The appearance of fallstreaks can vary depending on the type of precipitation and atmospheric conditions. They are often seen as wispy, tail-like extensions beneath the base of clouds.

The formation of fallstreaks is a result of a simple process. When precipitation, such as rain or snow, forms within a cloud, it begins to fall due to gravity. However, if the air below the cloud is dry and warm, the precipitation particles can evaporate as they descend. This evaporation cools the surrounding air, which can sometimes lead to the formation of small, localized downdrafts. The visual effect is a visible streak extending downwards from the cloud.

Fallstreaks are an indicator of the atmospheric moisture profile. The length and intensity of a fallstreak can provide clues about the humidity and temperature of the air. In some cases, the evaporation of fallstreaks can contribute to the cooling of the lower atmosphere, potentially influencing local weather patterns. While fallstreaks themselves do not reach the ground, their presence suggests that precipitation has formed in the cloud above. They are a common sight in fair-weather cumulus clouds, as well as in larger storm systems.