Mesocyclone Evolution Associated with Varying Shear Profiles during the 24 June 2003 Tornado Outbreak

Philip N. Schumacher NOAA/National Weather Service, Sioux Falls, South Dakota

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Joshua M. Boustead NOAA/National Weather Service, Valley, Nebraska

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Abstract

The morphology of mesocyclones associated with the regional tornado outbreak on 24 June 2003 is examined to illustrate the effects of changing vertical wind profiles. The large-scale environment supported deep moist convection, with forcing for ascent and convective instability. Postevent analysis indicated there were changes in the shear in space and time across a small geographical area. The event was separated into sectors based on both the synoptic setting and the differing shear profiles. Near the surface warm front, the vertical wind profile and mesocyclone evolution exhibited a classic appearance and produced significant tornadoes. In the warm sector, where no discernible surface boundaries were evident, classic supercells initially were favored but only produced short-lived tornadoes rated as F0 on the Fujita scale. The vertical wind profile changed as a low-level jet intensified after 0000 UTC 25 June. The majority of the vertical wind shear became located below 3 km. Meanwhile, mesocyclone elevation lowered and rotational velocity increased. As the dynamically induced low-level jet and an area of mixed-layer (ML) convective available potential energy (CAPE) became juxtaposed where the boundary layer was uncapped, strong low-level mesocyclones and 32 tornadoes developed in an area with no discernible surface boundaries. The event illustrates the need for warning meteorologists to monitor not only the amount of shear present, but also its distribution in the hodograph owing to its strong correspondence with mesocyclone morphology.

Corresponding author address: Philip N. Schumacher, National Weather Service, 26 Weather Ln., Sioux Falls, SD 57104-0198. E-mail: phil.schumacher@noaa.gov

Abstract

The morphology of mesocyclones associated with the regional tornado outbreak on 24 June 2003 is examined to illustrate the effects of changing vertical wind profiles. The large-scale environment supported deep moist convection, with forcing for ascent and convective instability. Postevent analysis indicated there were changes in the shear in space and time across a small geographical area. The event was separated into sectors based on both the synoptic setting and the differing shear profiles. Near the surface warm front, the vertical wind profile and mesocyclone evolution exhibited a classic appearance and produced significant tornadoes. In the warm sector, where no discernible surface boundaries were evident, classic supercells initially were favored but only produced short-lived tornadoes rated as F0 on the Fujita scale. The vertical wind profile changed as a low-level jet intensified after 0000 UTC 25 June. The majority of the vertical wind shear became located below 3 km. Meanwhile, mesocyclone elevation lowered and rotational velocity increased. As the dynamically induced low-level jet and an area of mixed-layer (ML) convective available potential energy (CAPE) became juxtaposed where the boundary layer was uncapped, strong low-level mesocyclones and 32 tornadoes developed in an area with no discernible surface boundaries. The event illustrates the need for warning meteorologists to monitor not only the amount of shear present, but also its distribution in the hodograph owing to its strong correspondence with mesocyclone morphology.

Corresponding author address: Philip N. Schumacher, National Weather Service, 26 Weather Ln., Sioux Falls, SD 57104-0198. E-mail: phil.schumacher@noaa.gov
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