A study of electrically severe thunderstorms (>2000 cloud-to-ground flashes per day) in the Spanish territory of Castilla-Leon (northern plateau of the Iberian Peninsula) has been performed using 11 years (2000–2010) of data. These episodes were classified according to average upper-level synoptic patterns. Seven synoptic patterns emerged: shortwave and very shortwave troughs, three types of lows, cyclonic vortex and ridge. The moisture content at low levels and static instability were also considered. In general, all the episodes were associated with instability and moderate moisture (11 g kg−1 for the average mixing ratio at 925 hPa). The electrically severe thunderstorms associated with five synoptic patterns (shortwave and very shortwave troughs, and three types of lows) generated hail, strong winds, and intense precipitation. By contrast, the cyclonic vortex and ridge synoptic types were not associated with severe weather.