A cross-section of the three-dimensional reflectivity of a thunderstorm shows the vault better. Algorithms were developed by the J.S. Marshall Radar Observatory of McGill University in Canada to locate the overhang region in a thunderstorm by the late 1980s. Its radar uses 24 angles, giving it good vertical resolution. In United States, fewer scanning angles are made within the WSR-88D radar which makes it more difficult to detect the overhang. Once the overhang is located, it is possible to make a cross-section to view if it is related with a BWER. However, since 1997 algorithms have been developed by the National Weather Service to determine regions of reflectivity gradient in three dimensions and the presence of BWER in convection.