A tornado climatology for Ireland

The results of detailed records and site investigations of reported tornadoes, waterspouts and funnel clouds over the last 3 years (1999–2001) are presented. Part of the analysis also includes the more fragmented record from 1950. These results are placed in the context of the potential for the atmosphere to produce the type of severe convective weather over Ireland often associated with tornadoes. This has been characterised from an analysis of daily values of several extreme weather parameters, namely Convective Available Potential Energy (CAPE), Bulk Richardson Number (BRN) and Severe Weather (SWEAT), derived from upper air soundings at Valentia. It is concluded that this potential is slight, though sufficient to produce moderately intense tornadoes at times. The analysis of the tornado record demonstrates that the annual frequency of such severe events is highly variable. Nevertheless, there have been many as 30 per year, although the average frequency of 10 per year may be more typical. In contrast to neighbouring countries, tornadoes mostly occurred during the summer months, especially August. It suggested that the strong monthly and diurnal patterns in the data might have more complex explanations than appears at first sight, when the particular climatic circumstances of Ireland are taken into account. Tornado intensities have ranged between T0 and T6 (F0 and F3) and a relationship between tornado intensity, track length and track width is considered. Finally, the geographical distribution of tornado and funnel cloud events is presented and an interpretation is given that considers the possible role of the terrain and land surface conditions in the development of atmospheric environments conducive for tornado events in Ireland.