The association of significant tornadoes with a baroclinic boundary on 2 June 1995

On 2 June 1995, the large-scale environment of eastern New Mexico and weste rn Texas was generally favorable for the occurrence of supercells because o f the presence of strong deep shear and storm-relative helicity, as well as sufficient convective available potential energy (CAPE). Indeed, many supe rcells occurred, but the only storms to produce tornadoes were those superc ells that crossed, or developed and persisted on the immediate cool side of a particular outflow boundary generated by earlier convection. Surface con ditions, vertical vorticity, and horizontal vorticity near this boundary ar e documented using conventional and special observations from the VORTEX fi eld program. It is shown that the boundary was locally rich in horizontal v orticity, had somewhat enhanced Vertical vorticity, and enhanced CAFE. Theo retical arguments indicate that the observed horizontal vorticity (around 1 x 10(-2) s(-1)), largely parallel to the boundary, can he readily produced with the type of buoyancy contrast observed. It is hypothesized that such local enhancement of horizontal vorticity often is required for the occurre nce of significant (e.g., F2 or stronger) tornadoes, even in large-scale en vironments that appear conducive to tornado occurrence without the aid of l ocal influences.