Synoptic patterns of severe hailstorm events in Spain

Abstract

A study of severe hailstorm (with size ≥ 3cm) over Spain has been conducted using 8 years (2012–2019) of data. The 73 events of heavy hail selected were classified using the moisture flux at the 850 hPa pressure level (qv) 850 and the lifted index (LI) as variables and a principal component analysis, coupled with a K-means clustering, as statistical technique. The application of this procedure provided four groups with their respective final cluster center. We took as the salient pattern of each cluster the case closest to each final cluster center. It was found that high values of low levels moisture flux (~ 89 g m/kg s on the average) are accompanied by static instability (SBCAPE ~ 600 j/kg and average LI ~ -4). The temperature values exceeded 20 ºC at the 850 hPa pressure level and range between -8ºC and -20ºC at the 500 hPa pressure level. The most typical configuration corresponded to geopotential and thermal trough at mean levels of the troposphere and low pressure at low levels. Likewise, high values of precipitable water (> 35 kg/m 2 ) have been detected and the presence of storm relative helicity and shear was moderate or strong in all cases.