Spanish Plume - June 2005
During the summer months we sometimes see a plume of very warm air adverted north from the region of Iberia, which becomes unstable as it moves up across France, into the UK and can give parts of the country some very unsettled thunder outbreaks. Sometimes though, the most severe weather can be restricted to a relatively narrow ‘corridor’, as in this case, across north eastern England and parts of the north and west Midlands.
During the 18th of June 2005, high 'theta-W' values moved north over Biscay and France and up across England. The values peaked on the 19th at or over 19C across the West Midlands and into NW England. These figures are very high and are not often exceeded across the British Isles. The lower levels of this air mass were also very moist from air that had originated in the deep tropics several days earlier.
Although the period was initially rather cloudy, with a considerable amount of mist and low cloud persisting across many areas, parts of England saw some brightness later in the day on the 17th and temperatures responded with a maxima of 28°C (82°F) reported at Shoeburyness, Essex. Much of England, Wales and Ireland after an overcast start, then enjoyed a very warm or hot summers day on the 18th with plenty of sunshine developing through the afternoon; there were some very high dew points and an oppressive muggy feel for most, especially overnight as temperatures remained above 18°C in parts.
The 19th dawned warm with clear skies with a plume of warm upper air situated across much of England and Wales; however a weak surface cold front began to approach from the west, introducing a much fresher air mass. Temperatures soared across much of the east and south-east with these locally as high as 33.7C at Wyton, (Beds), 33.1C at London Weather Centre (central London, Holborn) at 1600 and between 28C and 32C across much of England and Wales. The figure at Wyton was the highest June maxima recorded nationally since 2000 and the LWC figure, the highest June maxima in London since 1976.
A convergence zone developed across the north of England by the early afternoon initiating a line of deep convection and associated thunderstorms by around 1400, ahead of the weak cold front extending from Northeast Wales through Cheshire, Greater Manchester, Lancashire, and across much of Yorkshire. The thunderstorms generated a sudden drop in temperature of up to 10C in a matter of minutes in places, accompanied by gusty winds, large hail (around 1-2cm in diameter) and almost continuous thunder and lighning.
As the afternoon wore on the storms continued to progress slowly north-east and intensified further. Around 1700 across North Yorkshire there were some particularly violent storms which brought torrential falls of rain and caused considerable disruption to the area, especially to the south of the North York Moors National Park with villages such as Sutton-under-Whitestonecliff and the town of Helmsley particularly badly affected by floodwaters. Local totals in the area included 59.8mm in 1 hr at Hawnby and a 5 minute total of 12.0mm, and at Church Houses (10 miles NNE of Helmsley in the Nth York Moors) 44.1mm in an hour.
Temperatures remain high the following day in the south east (up to 28C) but somewhat cooler, fresher air gradually moved east across the whole country during the afternoon of the 20th.
