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The Spanish plume of 19th-20th June
A
very warm and moist air mass was advected North across the majority of the UK through the period 17th – 19th
June. Along with much warmer temperatures, a considerable amount of mist, murk and low cloud persisted across most parts for
much of the day, more especially around Southern and Western coasts – although parts of England saw some brightness
later in the day and saw temperatures respond with a maxima of 28°C ( 82°F) reported at Shoeburyness, Essex.
The
warm front located across Ireland and Southern Scotland
arched Northwards on Saturday affecting only the far Northwest of Scotland, Orkney and the Shetland Isles – where it
struggled to reach just 14°C. Much of England, Wales
and Ireland after an overcast start, enjoyed
a very warm or hot summers day with plentiful sunshine throughout the afternoon. The maritime origins of the air mass gave
some very high dew points and an oppressive feel for most, especially overnight as temperatures remained above 18°C in parts.
The
heat continued unabated with clear skies and the very warm plume very much still situated across much of England and Wales
throughout Sunday, however signs of a change were beginning out towards the far west. Overnight storms had occurred over parts
of West Scotland – but these had mostly dissipated by the morning as a weak surface
cold front began to approach from the West, introducing a much fresher air mass. Temperatures soared across much of the Southeast
with many London stations including Heathrow Airport and Northolt already reporting temperatures of 27°C by 09Z (10BST).
By mid-afternoon a pleasant sea-breeze had initiated across coastal parts of East Anglia and the South coast – however
much of the rest of England, Wales, East Scotland and more especially central London were baking, temperatures were locally
as high as 33.7C at Wyton, Beds, 33.1C at London Weather Centre in Holborn at 15Z and between 28C and 32C across much of England
and Wales. 33.7C was the highest June maxima recorded nationally since 2000 and the 33.1C the highest June maxima in the capital
since 1976.
Table
1 : Highest daytime maxima on the 19th June.
|
Station
Wyton
|
Maxima(°C)
33.7 |
|
London Weather Centre, Holborn
(Rooftop site) |
33.1 |
|
London Heathrow
Airport |
32.6 |
|
Northolt,
N London |
32.4 |
|
St. James Park, Cen. London |
32.4 |
|
Gravesend, Kent |
32.3 |
|
Conningsby,
Lincolnshire |
31.5 |
A convergence
zone across the North of England had initiated a line of deep convection by around 13Z ahead of the weak cold front in a line
extending NE from Northeast Wales through Cheshire, Greater Manchester, Lancashire, and across much of Yorkshire. The thunderstorms
generated brought a sudden drop in temperature of up to 10C (reported in places in a matter of minutes) accompanied by gusty
winds, large hail (above 1cm in diameter) and almost continuous thunder and lightning. Numerous reports were received suggesting
hail of up to 2cm in diameter falling locally, for which the potential had been forecast earlier in the day by the severe
weather agency 'TORRO'.
As the
afternoon wore on the storms continued to progress slowly NE and intensified further – over North
Yorkshire by around 16Z some particularly violent storms brought torrential falls of rain. This caused some considerable
disruption to the area. The worst affected area being located to the south of the North York Moors national park with villages
such as Sutton-under-Whitestonecliff, Thirlby and the town of Helmsley
particularly badly affected by floodwaters. An article with further information on this event can be found just here.
Local totals in the area included at Hawnby
59.8mm in 1 hr and a 5 minute total of 12.0mm, at Church Houses (10 miles NNE of Helmsley
in Nth York Moors) 44.1mm; at Westerdale (15 miles NNE of Helmsley on the North York Moors) 36.0mm and
at Brompton, Low Moor 33.2mm.
In the
south of England the skies remained relatively calm and clear and the night that followed was again warm and oppressive for
the southeast. Temperatures barely fell below 20°C by dawn and not even as low as that in the central urban area of London itself.
Table
2 : Highest overnight minima on 19th/20th June.
|
Station |
Overnight
Minima 19th-20th
(°C) |
|
London Weather Centre, Holborn
(Rooftop site) |
22.1 |
|
London Heathrow
Airport |
19.8 |
|
Langdon Bay |
19.7 |
|
Manston |
19.5 |
|
Northolt,
N London |
18.4 |
Temperatures remain high the following day in the SE
(up to 28C) but somewhat cooler, fresher air gradually moved east across the whole country during the afternoon of the 20th.
Dave Jamieson (C)
Many
thanks to Philip Eden and The Environment Agency for rainfall, temperature stats used.
Further detailed analysis of the synoptic development of
the events can be found here.
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