40C in London end of July? Probably not

The long range weather models are causing much excitement on various forums with one run predicting an anomaly of +16C on Sunday, July 29th.

july29th

Such an anomaly would see temperatures exceed 40C in London, unprecedented looking back at records to 1841; the highest temperature recorded in the UK was 38.5C at Brogdale, near Faversham, Kent, in Augut 2003.

Though it is improbable it is not impossible. Back in April conditions allowed the temperature to rocket to a monthly record of 29.1C, a positive anomaly of 15.5C!
A repeat of similar synoptic conditions would be needed – these would obviously be helped by the record meteorological drought conditions this area is currently experiencing.

Because reliable thermometer records of heatwaves only go back as far as 1840 it is impossible to quantify whether 40C has ever been exceeded in the UK prior to then.

However, accounts of the heatwave of July 1808 suggest parts of England may have come close. Far removed from images of freezing Georgian winters and miserable summers the July of 205 years ago was among the warmest ever. The monthly mean for July 1808, according to the Central England Temperature series, was 18.4C – the 6th hottest July since the beginning of the series in 1659.

Luke Howard, the ‘father of meteorology’ who at the time lived in Plaistow, referred to the heatwave in his diary on July 13th: “Temperature at 9am 84F. The intense heat of the maximum lasted nearly three hours till about 4pm. At 6pm the temperature was 90F.” Another entry mentions a reading taken nearby. “Another at Plashet, a mile and a half eastward, indicated 96F as the maximum under the shade of a house.”

While Howard’s methods of measuring the temperature ran short of modern standards, his thermometer was hung under a laurel bush, the values still give a valid insight into the heatwave.

Tales of the heatwave, which particularly affected east and north-east England, can be seen in letters sent to local newspapers around the country. Many describe labourers dying from heat exhaustion while working in fields. Farm animals and horses suffered a similar fate.

One letter from Hull, published in the Coventry Mercury, said: “At Sigglesthorne, the honey in some beehives melted, ran out upon the ground, and most of the bees drowned in it. At Sutton, a lamb and a dog belonging to the Rev Mr Croft of Rowley, expired in the heat; and several birds dropped down dead, while flying over the streets of this town.”
Of course it is impossible to know about the health of people and animals that died but that birds dropped out the sky suggests extreme heat.

 

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East London: drier than the Sahara desert

This summer has seen less than a millimetre of rain fall across our region, less than some parts of the Sahara desert!

The lack of precipitation has had catastrophic results, not least being a big contributing factor to the huge grass fire that swept through parts of Wanstead Flats at the weekend.

Since May 29th just 0.7mm has fallen in Wanstead, less than the 2.9mm recorded in Bechar, Algeria, and far less than Agadez in Niger which recorded nearly 108mm.

50 days

Of course the fact that the mean temperature of Wanstead over the same period is at least 13C cooler than both Saharan towns means that the dunes won’t be blowing across the Temple any time soon.

The affects of the dry weather can also be seen across the UK in these MODIS images, the lush greens of last year looking much paler and browner.

comparison

 

jul232014
MODIS image July 23rd 2014
jul152015
MODIS image July 15th 2015
jul192016
MODIS image July 19th 2016
jul172017
MODIS image July 17th 2017
jul152018
MODIS image July 15th 2018

 

 

 

London droughts back to 1871

A thunderstorm on July 27th has ended a dry spell that lasted nearly 7 weeks in east London. As storms go it was a fairly tame affair, just 1.3mm fell, the first rain in 47 days, 20 hours and 14 mins.

drought rankThere are many descriptions of drought but the one I am using here, for sheer simplicity of comparison back to 1871, is the definition used up until the 1990s; that is 15 consecutive days with less than 0.25mm (0.01 inches) rain on any one day.

Meteorological droughts occur in most years though obviously ones that occur in summer are far more noticeable than those in winter. Since 1871 there have been 35 calendar years where no drought has taken place.

The longest drought before this one in 2018, probably not surprising for those who remember it, occurred during the long hot summer of 1976. The fact that summer came on top of a very dry winter, rainfall that season was about a third of what was recorded here last winter, meant that water supplies were in a much worse state, with hosepipe bans common.

Other drought years to feature include 1959, which saw the 3rd sunniest summer on record, 1929 and 1995, a summer which saw one of the hottest heatwaves on record.

For the stats I’ve used local rainfall figures back to 1959 and then stats used at Kew to 1871.

individual droughts
This graphic shows droughts were most common between 2000 and 1921. Apart from this year the length of droughts seems to be declining

Looking at the results more closely I’ve divided them into their meteorological seasons.

spring drought

summer drought

autumn drought

winter drought

 

 

 

London’s July extremes since 1959

With the ultra dry and warm month of June many feel the rest of summer will remain hot and dry. Recent weather patterns have seen much high pressure to our north keeping us dry and mostly sunny but protected from any humid Spanish plumes.

A look at local east London stats shows that half of the last 10 July months have been warmer than average while only two have been much drier than average.

I’ve put together a few top 10s of stats for Wanstead, St James’s Park and Heathrow for the month of July.

july1959WAN

july heathrow

sjp july

Some national UK July values according to TORRO

 

Hottest: 19th 2006: 36.5C at Wisley, Surrey.
Coldest: 15th 1977: -2.5C at Lagganlia, Highland.
Wettest: 18th 1955: 279.4.8mm at Martinstown Dorset.

july av mxIn terms of climatology July maxima, considering the 1981-2010 average, shows a fairly steady increase through the month, though around the 17th there is often a dip before a warm end. This would reflect the July heatwave singularity which occurs every year at 80 per cent probability.

The average rainfall graphic shows that downpour amounts are fairly random from year to year. The driest days are the 1st and the 25th. july av rn

 

June 2018: driest on record since 1797

This June will probably be most remembered for the lack of rainfall throughout the month. I recorded just 0.7mm of rain over the 30 days – the driest June in a local record going back to 1797, 0.4mm less than the previous driest June in 1925.

fire
A fire on Wanstead Flats on Friday 29th was quickly extinguished thanks to the fire brigade

As I write this the area is now experiencing its 24th day of ‘meteorological drought’ conditions with little prospect of anything heavy anytime soon. The month was in stark contrast to May which saw may downpours associated with thunderstorms.

It was a warm month. The mean temperature finished 18.1C, exactly 2C above average, though slightly down on last June and the 7th= warmest since 1797.

Some 231.4hrs of sunshine were recorded, 130 per cent of average, making it the sunniest May for 8 years, and the 30th sunniest since 1881.

The warmest day occurred on the 25th with 30C.

The wettest day occurred on the 9th with 0.4mm falling.

Summary for June 2018

Temperature (°C):
Mean (1 minute)  17.7
Mean (min+max)   18.0
Mean Minimum     12.3
Mean Maximum     23.8
Minimum          6.4 day 12
Maximum          30.0 day 25
Highest Minimum  17.8 day 18
Lowest Maximum   17.9 day 04
Air frosts       0
Rainfall (mm):
Total for month  0.7
Wettest day      0.4 day 09
High rain rate   4.0 day 09
Rain days        1
Dry days         29
Wind (mph):
Highest Gust     18.3 day 14
Average Speed    3.1
Wind Run         2199.7 miles
Gale days        0
Pressure (mb):
Maximum          1029.9 day 21
Minimum          1008.2 day 14
Days with snow falling         0
Days with snow lying at 0900   0
Total hours of sunshine        231.4
Elsewhere in the UK it has been a very dry month across England.
0-25
Two CET stations, Rothamsted and Pershore recorded 2.2mm and 10mm respectively.
Other stations:
Northolt 0.8mm
St Bees Head: 25.2mm
Scilly: 7.6mm
Shoebury: 0mm