"A bow echo is associated with
squall lines or lines of convective
thunderstorms. These echoes can range in size from 20 to 200 km, and have a life span of 3 to 6 hours. Bow echoes tend to develop when moderate to strong
wind shear exists in the lower 2 to 3 km of the
atmosphere. While similar to squall lines, bow echoes are smaller in scale and are moved by the wind inside them. They tend to push outward and after time die out.
A bow echo also lowers the chance of a tornado being formed in the storm itself. The "bow shaped" echo is a result of focusing of the strong flow at the rear of the system.
[4] Especially strong bow echoes that cause devastating damage all along the width of the storm are often called
derechos."
"Damaging
straight-line winds often occur near the center of a bow echo. Damage from all severe thunderstorm winds accounts for half of all severe reports in the lower 48 states of the US, and is more common than damage from tornadoes. In a type of long-lived and powerful bow echo known as a
derecho, wind speeds can reach up to or exceed 100 mph (160 km/h) and can produce a damage path extending for hundreds of miles.
[6] Bow echoes are capable of producing straight-line winds that are just as strong as many tornadoes. Indeed, a strong bow echo will produce more widespread and intense damage than the majority of tornadoes. Also, bow echoes in the form of a
line echo wave pattern create a favorable environment for tornadoes to form."