Abstract
Abstract A climatology is developed for tornadoes during 1980–2012 in the British Isles, defined in this article as England, Scotland, Wales, Northern Ireland, Republic of Ireland, Channel Islands, and the Isle of Man. The climatology includes parent storm type, interannual variability, annual and diurnal cycles, intensities, occurrence of outbreaks (defined as three or more tornadoes in the same day), geographic distribution, and environmental conditions derived from proximity soundings of tornadoes. Tornado reports are from the Tornado and Storm Research Organization (TORRO). Over the 33 years, there were a mean of 34.3 tornadoes and 19.5 tornado days (number of days in which at least one tornado occurred) annually. Tornadoes and tornado outbreaks were most commonly produced from linear storms, defined as radar signatures at least 75 km long and approximately 3 times as long as wide. Most (78%) tornadoes occurred in England. The probability of a tornado within 10 km of a point was highest in the south, southeast, and west of England. On average, there were 2.5 tornado outbreaks every year. Where intensity was known, 95% of tornadoes were classified as F0 or F1 with the remainder classified as F2. There were no tornadoes rated F3 or greater during this time period. Tornadoes occurred throughout the year with a maximum from May through October. Finally, tornadoes tended to occur in low-CAPE, high-shear environments. Tornadoes in the British Isles were difficult to predict using only sounding-derived parameters because there were no clear thresholds between null, tornadic, outbreak, and significant tornado cases.
Highlights
Tornadoes in the British Isles have been labeled as ‘‘freak’’ occurrences by the media (Elsom 1985), the United Kingdom has been cited as having more tornadoes per area than any other country in the world (Reynolds 1999)
D Tornadoes were most common in summer and autumn, whereas tornado days were most common in summer
Tornadoes occurred throughout the year, so the British Isles tornado season was not as well defined as the United States
Summary
Tornadoes in the British Isles have been labeled as ‘‘freak’’ occurrences by the media (Elsom 1985), the United Kingdom has been cited as having more tornadoes per area than any other country in the world (Reynolds 1999). Temporal analysis of tornadoes has been conducted before in the British Isles (Table 1) These climatologies reported average annual occurrence of tornadoes ranging from 10.3 tornadoes per year (Ireland, 1999–2001; Tyrrell 2003) to 47.2 tornadoes and waterspouts per year (United Kingdom, 1981–2010; Kirk 2014). The only research on environmental conditions associated with tornadic storms have been case studies (e.g., Bolton et al 2003; Clark 2012) or were based on reanalysis data over short periods and large areas (e.g., Brooks et al 2003b; Romero et al 2007) This article addresses these gaps in the research by including storm type and proximity sounding analyses. In the absence of a site investigation or photographic or video evidence, an environmental situation conducive to tornadoes would designate the report as probable This article uses both definite and probable reports, similar to Elsom and Meaden (1984) and Kirk (2014)
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