13 May 2010 Severe Bow Echo Event Over Northeast Oklahoma Part 1: Synoptic and Mesoscale Environment

Two bow echoes embedded within a large quasi linear convective system (QLCS) moved rapidly across parts of central and eastern Oklahoma during the early morning of 13 May 2010. The northern and larger bow echo was responsible for producing damaging winds and several QLCS tornadoes. The tornadoes occurred along the leading edge of the bow over parts of northeast Oklahoma, including the Tulsa metropolitan area. These tornadoes developed on the portion of the bow echo between the apex of the bow northward to the bow's intersection with a quasi-stationary surface boundary.

The 13 May 2010 convection evolved in a strongly dynamic and moderately unstable environment. At 0000 UTC 13 May, the 300-hPa analysis showed a upper trough extending from a low center across the western Dakotas southwestward through the southern Rockies. A 40-45 ms-1 upper-level jet streak stretched from western South Dakota through eastern Colorado. Subtle mid-level shortwave troughs and associated speed maxes were noted rotating through the larger trough. A southerly, 18 ms-1 850-hPa low-level jet of was advecting dewpoint temperatures of 14-18°C from west Texas northward through Oklahoma. Surface analysis at 0000 UTC revealed a low pressure center near Amarillo, Texas, with a cold front extending northeastward through northwest Oklahoma and south-central Kansas toward Kansas City. Strong to severe convection had developed in vicinity of the frontal zone during the late afternoon hours through early morning hours on 12-13 May 2010. The 0000 UTC Norman, Oklahoma (OUN) sounding showed a shallow elevated mixed layer above 840-hPa and a deep moist layer above 600-hPa. Mixed layer convective available potential energy (CAPE) values exceeded 2500 J kg-1 while deep-layer shear (0–6km) topped 27 ms-1. This CAPE axis extended east and northeast along the surface frontal zone as sampled by the 0000 UTC Springfield, Missouri (SGF) sounding. The elevated mixed layer was warmer with southward extent as sampled by the Fort Worth, Texas (FWD) 0000 UTC sounding. Deep-layer shear sampled at both SGF and FWD showed decreasing values to the south and east of the approaching upper trough.

This paper will describe changes in the synoptic and mesoscale environments between 0000 UTC and 0900 UTC on 13 May 2010 focusing on the development of an MCS over west-central Texas that moved rapidly northeastward, eventually into northeast Oklahoma. We will utilize numerical model initialization data, infrared satellite imagery, and Storm Prediction Center (SPC) mesoscale analysis prior to the bow echo passing through the Tulsa metropolitan area and points northeast.

We will also explore the 0-3 km shear vector application in capturing the location of the greatest threat for tornadogenesis. Preliminary findings show that the 0-3 km shear vectors with magnitudes of 20 ms-1 were oriented nearly normal to the bowing of the convective line south of the intersection of the outflow boundary and bow echo. From previous studies and cases, this is a preferred region for tornadic mesovortexgenesis.

Finally, the local numerical model data produced at the Tulsa, Oklahoma Weather Forecast Office will be used to show the overall evolution of the event. Simulated radar reflectivity, updraft helicity, and maximum surface wind fields from the model will be shown. Additionally, cross-sectional analysis within the model fields will be shown as an example of model simulated QLCS structure. These fields will be presented to show several evolutionary changes in the reflectivity and surface wind patterns that compared favorably to actual observations.