THE CG LIGHTNING ACTIVITY OF A STORM CAUSING A FLASH-FLOOD

On August 7, 1996, a flood of the Rio Gallego, in Aragon (Spanish cent ral Pyrenees) wiped out the Biescas' campground, killing more than 80 persons. From the observations of two meteorological radars, this thun derstorm exhibited some of the radar characteristics of a supercell. I t spread almost exactly over the Rio Gallego catchment area, up-stream of Biescas, and it remained above this area for about two hours, with out any advection. The rainfall reached 100 mm h(-1) and the total cum ulative amount locally reached 200 mm. The cloud-to-ground (CG) flash density averaged over 5 x 5 km(2) areas, was exceptionally high, aroun d 2 km(-2), and the peak flash rate averaged over 5-minute periods rea ched 11.6 min(-1) within the cell area. The evolution of the CG flash rate and the radar reflectivity were closely correlated. The flash rat e reached high values before the arrival of the precipitation at the g round. We observe also a very good agreement between the location of t he intense rain at the ground and the high CG flash density. The rainf all water volume per flash was 3x10(4) m(3), a value in agreement with previous work. We propose that quantitative measurements of the light ning activity may provide valuable information for flash-flood nowcast ing and short-term forecasting in mountainous areas.