Session 18.4 An elevated supercell with damaging wind reports from the morning of 12 March 2006

Friday, 10 November 2006: 2:15 PM
St. Louis AB (Adam's Mark Hotel)
Stephen M. Goss, SPC, Norman, OK; and R. L. Thompson and E. M. Bookbinder

Presentation PDF (447.0 kB)

An intense, elevated supercell thunderstorm formed the morning of 12 March 2006 near Lawrence, Kansas, and moved to the east-northeast across the Kansas City metropolitan area into north central Missouri. Local surface observations and soundings suggest that the convection was rooted above a frontal inversion and forced by pronounced warm advection to the north of a surface warm front located across northeast Oklahoma and southern Missouri. Despite the elevated nature of the convection and surface temperatures in the upper 40s to lower 50s F, significant wind damage was reported along the path of the storm in northeast Kansas and northwest Missouri.

Damaging winds are rarely considered to be a substantial threat with elevated convection due to the presence of a near-ground stable layer. However, a close examination of this case suggests that unique characteristics of the near-ground stable layer were critical to the damaging wind threat. Regional soundings illustrate a steep, but shallow frontal inversion beginning immediately above the surface, topped by a layer of very steep lapse rates and large potential instability. The combination of large elevated CAPE and strong vertical wind shear above the frontal inversion provided an environment very favorable for elevated supercells. The unique thermodynamic profiles also supported large downdraft CAPE values despite the near-surface stable layer. Local surface observations in the vicinity of this specific supercell revealed a meso-gamma high pressure center within the storm's rear flank outflow, with surface temperatures the same or warmer than pre-storm environment. The warmer temperatures within the storm outflow suggest the possibility of “overshooting downdrafts” of mid-level origin. This same mechanism may also help explain occurrences of damaging winds along the cool side of surface boundaries with larger convective complexes.

We will also provide documentation of a tornado produced by this supercell as it traveled northeast of Kansas City into Ray County Missouri. This may be the only well-documented tornado with an elevated supercell, in an environment with no surface-based CAPE, in the past few decades.

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