Shear Assessment » Bulk Richardson Number (BRN) Definition
Definition: Bulk Richardson Number (BRN)
The Bulk Richardson Number (BRN) is the ratio of the buoyancy (as measured by the CAPE) to the vertical wind shear of the environment. As we have noted previously, updraft strength is directly related to CAPE, while the storm structure (e.g., multi-cell, supercell, etc.) and movement are related to the vertical shear.
The Bulk Richardson Number (BRN) is the ratio of the buoyancy (as measured by the CAPE) to the vertical wind shear of the environment. As we have noted previously, updraft strength is directly related to CAPE, while the storm structure (e.g., multi-cell, supercell, etc.) and movement are related to the vertical shear.

This graphic shows BRN values related to storm type. Generally, if the BRN is less than 10, there is much more shear than buoyancy, and the storms tend to be torn apart by the shear. The exception is in strongly forced, high-shear, low-CAPE environments where supercells are observed with BRN values less than 10. With BRN between 10 and 35, the balance between shear and buoyancy tends to favor supercells. With BRN greater than 50, buoyancy dominates over shear and single- or multi-cell storms are more likely to be observed.