Bounded weak echo region

The bounded weak echo region, also known as a BWER or a vault, is a radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm. It cannot be seen visually. The BWER has been noted on radar imagery of severe thunderstorms since 1973 and has a lightning detection system equivalent known as a lightning hole.

The BWER is a nearly vertical channel of weak radar echo, surrounded on the sides and top by significantly stronger echoes. The BWER, sometimes called a vault, is related to the strong updraft in a severe convective storm that carries newly formed atmospheric particulates, called hydrometeors, to high levels before they can grow to radar-detectable sizes. BWERs are typically found at mid-levels of convective storms, 3 kilometres (1.9 mi) to 10 kilometres (6.2 mi) above the ground, and are a few kilometers in horizontal diameter. Identifying the location of the updraft region is important because it is linked to locations where severe weather normally occurs. The presence of a BWER has been part of a method to diagnose thunderstorm strength as part of the Lemon technique since 1977. The updraft strength within the BWER supports the growth of large hailstones just above the vault, which can be displaced slightly into the direction of motion of the parent supercell storm.

The bounded weak echo region (BWER) is a region of low radar reflectivity bounded above by an area of higher radar reflectivity which shows evidence of a strong updraft within mesocyclones. Radar analysts have recognized this phenomenon since at least 1973, using different elevation scans. Methods of objectively corroborating that a BWER is associated with a mesocyclone is done by using a weather radar with Doppler effect to obtain the precipitations velocities. This have been available operationally in United States since 1997 with the NEXRAD network. When using the lightning detection system, lightning holes (uncovered in 2004) correspond to where a BWER would be seen on radar.

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