A Climatology of Tornado Outbreaks from Narrow Cold-Frontal Rainbands in the UK

A Climatology of Tornado Outbreaks from Narrow Cold-Frontal Rainbands in the UK

A 10-year climatology is constructed for tornado outbreaks (classified as days with 3 or more tornadoes) originating from Narrow Cold-Frontal Rainbands (NCFRs) in the British Isles from 2005-2015. This climatology focuses on the intensity, geographical distribution and the environmental conditions assessed with model (WRF) simulations and proximity soundings. All tornado reports are from the Tornado and Storm Research Organisation (TORRO). NCFRs were defined as linear features from the UK radar network NIMROD with a length greater than 100km, at least 10 times longer than wide and a minimum duration of 2 hours. Ten NCFRs matched this criteria, with 8 occurring during winter/spring. From the outbreak records, there were 68 associated tornado reports of which 44 were given a classified strength, 86% of these being given a strength of EF0-EF1, with the remaining as EF2. There were no EF3+ reports. A majority of tornado reports occur in the south-east of England, yet outbreaks are not isolated to this region with reports occurring across most of the United Kingdom. All ten outbreaks exhibited precipitation cores and gaps along the cold front. This structure on the radar has been associated with tornadoes in the previous literature, with the precipitation cores being associated with misovortices responsible for the tornadoes. These misovortices form in an environment of low CAPE and high shear. Strong cross-frontal wind veering as well as a strong cross-frontal temperature gradient is also observed for each outbreak.