A Tornadic Thunderstorm in the Complex Terrain of Southcentral New Mexico

On June 7, 1997 an unusual severe thunderstorm event occurred in Southern New Mexico and Far West Texas. Severe convection of this type is rare in the desert region of the Southern Rocky Mountains and even more unusual since this event occurred before the onset of the more moist summer monsoonal flow. The upper tropospheric pattern at 1200 UTC was atypical, with a split flow over the Western United States. While the primary polar jet stream extended across the Northern Rockies, a southerly branch of the upper flow traversed through Southern California and Northern Baja into Arizona and Southern New Mexico. With the upper low situated over Arizona, and the surface low forming in Western New Mexico, deep tropical moisture advected into the region. Late in the day, along a developing dryline and underneath an area of upper-level diffluence, severe thunderstorms initiated near Las Cruces, New Mexico and moved eastward. These storms interacted with the Organ Mountains and it is believed that this case is one of the few cases where a rotating thunderstorm crossed a significant mountain barrier, taking advantage of downslope easterly winds in the formation of the initial rotation on the west side of the mountain and then having an upslope/downslope interface on the eastern side of the mountain chain. Tornadic formation occurred well after the main gust front had moved into the valley, with the tornado developing under the southwestern flank of the complex at an elevation about 700 ft above the valley floor. While local observations indicate significantly rain-cooled air in the area, it is likely tornadogenisis occurred at a depth above the colder air in a region of upslope along the side of the mountain. This paper and discussion will investigate this fascinating interaction of synopticscale and mesoscale environments in complex terrain.