CAPE values and hailstorms on northwestern Spain

A study has been carried out in Leon (in the northwest of the Iberian Penin sula) on atmospheric convection during summer periods, by analyzing the val ues of the Convective Available Potential Energy (CAPE) around 07:00 UTC. T he project analyzed the data provided by a network of voluntary observers, a hailpad network, and a meteorological station on a sample of 224 days, Th e CAFE values found were not high: they never reached 2000 J/kg, not even o n hail days, i.e. on days with high convective activity. These values are m uch lower than the ones measured in convective situations in tropical regio ns, but they are within the usual values found in Europe, The same happens with the wet bulb potential temperature measured in Leon. The frequency dis tribution of the CAFE values shows a clear prevalence of very low or zero v alues. The group of days with the lowest CAFE value is that which included days with no storm. The mean value increases on storm days, and it is even higher for the days with recorded hailfalls. All these differences are sign ificantly marked. Nevertheless, the differences across the years are not si gnificant enough to be able to speak of an influence of the climatic change on the CAFE. The correlation of the CAFE with some of the variables previo usly used For hail forecasts was analyzed, and the correlation found was hi gher for the lifted index, The possible use of the CAFE as a thunderstorm a nd hailstorm forecasting method was considered. The results were encouragin g, especially for hail forecasting, although the CAFE should not be used as the only variable, but combined with other parameters. Moreover, the relat ionships between the CAFE and the wet bulb potential temperature and betwee n the CAFE and the physical parameters of the hailstones were also analyzed . A relationship was observed with the parameters of the hailstone size dis tribution, Nonetheless, these results are provisional, and they should be c onfirmed by analyzing a more representative sample, With a more detailed an alysis of these and other relationships, the present forecast model used by the Laboratory for Atmospheric Physics at the University of Leon is dexpec ted to be greatly improved by including the CAFE in this model. (C) 2001 El sevier Science B.V. All rights reserved.