Dual rear inflow jets within the 26 August 2003 derecho

On 26 - 27 August 2003, a mesoscale convective system (MCS) produced a bow echo that resulted in a widespread swath of damage across the Midwestern United States. The MCS that produced these winds initiated in north-central Illinois. Damaging winds were first reported along the Indiana-Michigan border, with subsequent reports along a swath extending east-southeastward through northern Ohio and into western Pennsylvania, northern West Virginia, and far western Maryland. A total of 87 counties reported damaging winds. The exceptionally widespread damage from straight-line winds, and the nature of the damage qualified this event as a derecho.

The MCS displayed a feature that has not been documented in past studies: dual rear inflow jets (RIJs) at different altitudes. The dual RIJ structure was concurrent with the most concentrated surface damage. The upper branch descended gradually from ~9000 m at the rear of the system to ~5000 m about 15 km behind the leading convective line, while the lower branch descended from ~5500 m at the rear of the system to ~1500 m about 50 km behind the leading convective line, reaching the surface at the convective line, based on surface wind reports. In this paper, WSR-88D level-II data are used to document the dual RIJ structure.