20. April 2012 was characterized by steep lapse rates and enough moisture for 300-400 J/Kg CAPE to be materialized. Most of the UK was under the influence of a mid-level trough with a broad surface low which was centered over the east coast of the UK in Lincolnshire, leading to weak flow and wind shear. Such weak flow conditions are favorable for vortex stretching, if vorticity can develop by some mechanisms, which can lead to spout-type tornadoes and funnel clouds (these are very weak tornadoes and funnels not associated with supercells). One mechanism that can develop horizontal vorticity are sea-breezes. These form when solar radiation heats up land that warms much faster than surrounding seas and oceans. The temperature contrast then forms the sea-breeze – a mini-cold front which then spreads inland and forms horizontal vorticity on its leading edge. The same front can trigger shower and thunderstorm activity the updrafts of which can tilt and stretch this vorticity to form funnel clouds and tornadoes.
Because of the conditions described above, I decided to chase storms along the east-coast sea-breeze in east Yorkshire and Lincolnshire. I took the M62 to near Hull and then went over the Humber Bridge to intercept some showers that developed into thunderstorms and produced a funnel cloud. A more detailed description of this event can be found here in Czech only!