The July 1968 United Kingdom thunderstorms were the most severe dust fall thunderstorms in the British Isles for over 200 years. A layer of mineral dust blowing north from the Sahara met cold, wet air over the British Isles, resulting in thick, dense clouds and severe thunderstorms across most of England and Wales. These clouds completely blotted out the light in some areas and the rain and hail resulted in property damage and flooding, and at least four people were killed. During the storm, Leeming Bar in North Yorkshire saw of rain in under 10 minutes – a UK record until 2003. Meteorology The Hoggar Mountains in Algeria saw a number of severe thunderstorms on 26–27 June. These appear to have blown a large quantity of Sahara dust into the atmosphere, where it was caught in a southerly wind in an atmospheric layer between and in altitude, forming a classic Spanish plume. Unusually, no clouds formed as this dust blew over continental Europe, and the layer reached England on 30 June largely unrained out. The warm desert air brought a heatwave over Southern England, with temperatures in London on 1 July measured at , until it met the much cooler, moister Atlantic airstream. The boundary between the two formed a squall line stretching from Devon, along the England–Wales border and up across Northern England to the River Tees. Thick clouds, darkened by the Sahara dust, rose to , plunging areas along the squall line into total darkness. In some areas, the lightning continued for 24 hours, and ball lightning was seen at RAF Chivenor in Devon. The dust particles served as seeds for nucleation, causing water to rapidly precipitate out and form especially large raindrops and hailstones. The thunderstorms resulted in one of the most widespread intense hail falls ever recorded in the UK, with hail events in 9 separate places reported as "severe" (H3) or greater on the TORRO hail scale, and the strongest rated "destructive" (H6). Hailstones across – the size of a tennis ball – were measured at Cardiff Airport, and the local newspaper for Hartland, Devon, reported the finding of "a piece of ice long". Along with the hail came heavy rain, with the 9 minute fall at Leeming Bar setting a record for a sub-10-minute total. The Isle of Man measured of rain over the 48 hour time period associated with the storms. Areas south