The Sigüenza tornado: a case study based on convective ingredients concept and conceptual models

Abstract

On 24 May 1993, part of the Iberian Peninsula was affected by convective activity concentrated on the eastern side of a low-level thermal boundary which was orientated north–south. A series of storms evolved into a squall line striking at the province of Guadalajara (Central Spain). The southernmost cell of this mesoscale convective system generated a tornado that hit the city of Sigüenza between 1930 and 1940 UTC. This paper has two objectives. The first aim is to investigate the ingredients (buoyancy, wind shear, vertical distribution of moisture content, and synoptic and mesoscale lifting mechanisms) and the atmospheric agents (mid-upper level trough, low level-boundary, convergence zones, etc.) which favour the production of severe storms. The second one is to analyse information provided by operational remote-sensing systems (satellite, radar and lightning) in order to test and evaluate some conceptual models of severe storms in an operational environment. For the first objective, the ingredient-based methodology will be shown to be a valuable operational approach allowing forecasters to focus on the possibility of a severe event using the appropriate diagnostic or prognosis tools. For the second objective, special attention is given to the suitability of conceptual models associated with convective phenomena and the potential value of such models (lightning charge related to wind shear and radar-based multicell conceptual models) for understanding the observed processes. From an operational viewpoint some problems may arise because of the technical characteristics of the equipment, particularly related to radars (e.g. scanning strategy, distance between radar and targets, and radar signal processing and displaying). Possible guidelines for using volumetric radar data (non Doppler) for deep convection monitoring are suggested for rugged and complex topographical regions.