Seinäpilvestä

Seinäpilvestä is a Finnish term that translates to "wall cloud" in English. It is a distinctive feature that can form beneath a cumulonimbus cloud, specifically within a supercell thunderstorm. A wall cloud is a localized, persistent lowering of the cloud base that is often accompanied by a slight rotation. Its presence is a significant indicator of potential tornado development.

Wall clouds are typically observed as a smooth, ominous-looking area of cloud lowering from the main storm base. They can vary in size and shape, but often appear as a funnel-shaped appendage. The rotation associated with a wall cloud is crucial; if the rotation becomes more pronounced and concentrated, it can lead to the formation of a tornado. Meteorologists closely monitor wall clouds for signs of rotation, such as inflow streamers or a visible condensation funnel extending downwards.

The formation of a wall cloud is a complex process involving updrafts and downdrafts within the thunderstorm. The intense updraft in a supercell can draw moisture from lower levels upwards, creating a region of concentrated cloud formation. The rotating updraft, or mesocyclone, can cause this lowering. Not all wall clouds produce tornadoes, and the exact conditions that lead to tornado genesis from a wall cloud are still an area of active research. However, encountering a wall cloud is a strong signal for storm spotters and the public to be particularly vigilant and prepared for the possibility of a tornado.