Climatology of Tornadoes in the British Isles (1980–2012)

We present a climatology for tornadoes in the British Isles, defined here as England, Scotland, Wales, Northern Ireland, Republic of Ireland, Channel Islands, and the Isle of Man. The climatology includes the geographic distribution, annual and diurnal cycles, seasonality, intensities, and occurrence of outbreaks in tornadoes from 1980–2012 (from Tornado and Storm Research Organisation or TORRO data) as well as environmental conditions from proximity soundings (from Met Office UK High Resolution Radiosonde data). Over the 33-year period of study, there were 1241 tornadoes reported in the British Isles over 642 tornado days (number of days in which at least one tornado occurs). This computes to a mean of 37.6 tornadoes and 19.5 tornado days annually.

Most (78.3%) British Isles tornadoes occur in England with apparent maxima along the southern coast and in the east England. Of the remaining tornadoes in the dataset, 7.0% were in the Republic of Ireland, 6.7% in Wales, 4.8% in Scotland, 1.8% in Northern Ireland, 1.2% in the Channel Islands and 0.1% on the Isle of Man. To compare tornado occurrence between countries, the average annual tornado occurrence per 10,000 km2 was computed for each country making up the British Isles. England experiences 2.3 tornadoes per year per 10,000 km2, which compares to 3.5 tornadoes per year per 10,000 km2 in Oklahoma (1991–2010) [1].

Where intensity data is known, 95.3% of tornadoes were classified as EF0 or EF1 with the rest classified as EF2. There were no tornadoes rated EF3 or greater during this time period. Similarly, most tornadoes in the United States are on lower end of the Enhanced Fujita scale, with 95% of tornadoes in the United States rated below EF3, [1]. The United States is known to have EF5 tornadoes, but these tornadoes make up only 0.1% of the database [1]. So while tornado occurrence, at least by area, is similar to parts of the United States, central US tornadoes can be stronger than those seen in the British Isles. In the British Isles, the maximum monthly tornado frequency occurs in November. However, seasonality based on tornado frequency can be skewed due to multiple tornadoes occurring during a single day. Therefore, a tornado day analysis was conducted. Approximately half the tornado days in the British Isles occur from June to October with 23% of all tornado days occurring in August and September. This is later than the springtime maximum in the central and southern US and mid-summer in the northern US [2, 3]. Tornado outbreaks (defined as a day in which three or more tornadoes occur) occur year-round with a maximum in November and minimum in May. The highest number of tornadoes in an outbreak during the period of study was 104 tornadoes on 23 November 1981.

Proximity soundings will be examined, with the goal of understanding the environments within which tornadoes occur in the British Isles.

Citations 1. National Climatic Data Center, 2013: US tornado climatology. Tech. Rep., http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html 2. Brooks, H. E., C. A. Doswell and M. P. Kay, 2003: Climatological estimates of local daily tornado probability for the United States. Weather and Forecasting, 18, 626-640. 3. Suckling, P. W. and W. S. Ashley, 2006: Spatial and temporal characteristics of tornado path direction. The Professional Geographer, 58, 20-38.