<P> 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 . Especially strong bow echoes that cause devastating damage all along the width of the storm are often called derechos . </P>
<P> 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 . Especially strong bow echoes that cause devastating damage all along the width of the storm are often called derechos . </P>
which part of the mcs produces the bow echo on radar
which part of the mcs produces the bow echo on radar
the rear of the system
the rear of the system