Tag Archives: wanstead_meteo

July 2016: rather warm and very dry

There was plenty of interest in the weather last month even though the overall stats suggest July 2016 wasn’t that remarkable.

july 9 sky
The sunset on July 9th was spectacular

Most notable was temperature: the warmest minimum on record for this area (21.1C) was recorded during the early hours of the 20th – coming hours after the hottest day of the year: 33.5C – the 14th hottest day on record. The mean temperature of 19.5C  was a degree warmer than average, the 18th warmest July since 1797.

Rainfall was very sparse. A total of 17.3mm fell during the month, that’s 40 per cent of average, the driest for six years and the 19th driest in the series going back to 1797.

After a very dull start to the month sunshine was always going to struggle: just under 172 hours were recorded – that’s 89 per cent of average and marginally down on last July.

Air frosts: 0, Ground frosts: 0

record warm min
The temperature didn’t fall below 21.1C on the night of 19th July, making it the warmest minimum on record in this area back to 1959

So what has August in store weatherwise? The models on the 1st suggest the month will start with a mixture of sunshine and showers. At the end of this week there are indications of a change to warm and later very warm weather.

Beyond the grasp of the models my long range outlook method is hampered this month because of the very dry July. However, the data I do have suggests a rather warm month at 50 per cent probability. The ‘worst case’ scenario suggests something average, a contrast to  the past couple of Augusts which have been poor. Perhaps we can look forward to another reasonable summer month, defined by plenty of fine, at times hot, weather – though anyone looking for unending days of 30C and higher will be disappointed.

A dryer than average month (possibly very dry) looks most likely at 50% probability. A very sunny month looks most probable.

So to sum up: mean 19C (0.8C above average), rainfall 30.3mm (60%), sunshine 239 hours (123%).

hottest dayMy July outlook for temperature was good. I predicted a mean of 18.8C (outcome: 19.5C). Rainfall was very poor: 50mm (outcome: 17.3mm). Sunshine not badr: 171.9 hours (outcome: 190 hours).

Here follows the full weather diary for July…Full stats for the month here:http://1drv.ms/1rSfT7Y

1st: Cloudy with sunny intervals. Some sharp showers.
2nd: Bright start though breezy. Very heavy shower at 1740.
3rd: Sunny though with lots of cumulus.
4th: Sunny, gin clear start though cumulus rolled in at 1.30pm.
5th: Cloudy start with very brief, very light drizzle though with sunny breaks developing.
6th: Hazy mix of cirrus and cumulus gradually decreased to a clear sky by 1pm. More cumulus bubbled up later but still mostly sunny and low humidity.
7th: Sunny start with lots of cumulus, cirrus and stratus around. Sunny spells through the day.
8th: Cloudy and breezy start.hants
9th: Bright start with sunny spells but also lots of cloud. Amazing sunset with fronts coming in.
1oth: Cloudy start with light rain spreading in but only lasting for 40 minutes. Some sunshine in the afternoon though was breezy.
11th: Cloudy start with heavy showers early afternoon.
12th: Sunny start though with plenty of cloud which bubbled up and gave heavy showers from 11.30am. More showers in the afternoon – miserable.
13th: Bright and sunny to start that cloud gradually built before heavy showers hit at 2pm, these lighter over Aldersbrook.
14th: Sunny, bright start with sunny spells, tending to turn cloudier.
15th: Bright start but cloud piled in and breeze picked up.
16th: Sunny start with lots of cirro-cumulus. Cloud tended to build at times and a front passed over at 4pm. Warm evening and night.
17th: Bright start though with lots of heavy cumulus around. This tended to break up at intervals during the day, making it feel hot in the sun because of the high humidity.
18th: Sunny start with patchy cirrus and cumulus. This decreased as day wore on leaving a hot day. Felt almost airless with variable cloud.
19th: Sunny with decreasing cirrus to start to leave a gin clear day. Breeze picked up at noon meaning it wasn’t as warm as it could have been.
20th: Sunny but hazy start but with more of a breeze than yesterday. Cloud tended to fill in but then burnt off to leave another hot day.
21st: Sunny but cooler start than yesterday with lots of milky cumulus around.
22nd: Cloudy start after overnight rain. Sun breaking through at 12.30pm.
23rd: Cloudy start with spots of drizzle at 11am then slowy getting brighter with evening sunshine.
24th: Cloudy start with early showers breaking to sunny spells.
25th: Sunny start with variable amounts of cloud through the day. Feeling cooler.
26th: Sunny start though with cloud bubbling up through the morning. Overcast by 2pm.
27th: Cloudy and damp with light rain before and after obs time.
28th: Sunny periods with variable cumulus
29th: Cloudy start with brief rain showers in Chigwell. Sky broke to allow long sunny spells before it clouded over again. Rain shower at 9pm.
30th: Cloudy and overcast start. Long sunny spells into the afternoon.
31st: Sunny start though more cloud tending to bubble up in the afternoon.

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Heatwave? washout? Or just another changeable British summer?

chicken cloudWith all the talk of heatwaves this week it won’t be long before the media switches from piping on about the UK facing “10 years of miserable summers” to “Is our climate getting warmer?”.

But the simple fact is that the UK’s climate has always varied greatly – some years, as in the last two, the pattern for summer has brought mostly miserable weather. Other years we get a run of warm, dry summers.

A case in point was the heatwave of July 1808. 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.

Readings taken by Luke Howard at Plaistow show the build up of heat to the 14th. The series on the right, taken in Wanstead, around 3 miles to the north-east, will be added to by the author as July unfolds
Readings taken by Luke Howard at Plaistow show the build up of heat to the 14th. The series on the right, taken in Wanstead, around 3 miles to the north-east, will be added to by the author as July unfolds
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.

screenWhile temperature records of July 1808 are not unheard of in an English summer one record that remains is the size of the hail – which fell in damaging storms when a thundery breakdown arrived on the 15th.

The main storm missed Wanstead and the surrounding area – though Howard, writing in his Plaistow observatory, knew the weather was on the turn: “Dew on the grass, a fine breeze from ENE. Much lightning in the west this night, a few drops of rain.” Howard would have been referring to all the action about 120-odd miles west where one of the most ferocious storms in recorded history was unfolding.

Much was reported in the local press on the days following the storm which affected an area from Somerset northwards. As well as local records Luke Howard also noted national events in his diary: “After several days of uncommon and oppressive heat the city of Gloucester experienced a storm of thunder and lightning which extended many miles round and exceeded in awful phenomena any one remembered for many years past.”

Trees were “shivered to atoms”, livestock killed by lightning, crops were ruined and countless windows and glasshouses smashed by huge hailstones. A lot of the detail of the storm was compiled by a man named Crocker, then governor of Frome school, Somerset. One account from Batcombe describes a hailstone that measured 13.5 inches in circumference. To give you an idea of the size of a 342mm circumference hailstone I, with the help of my daughters, made one of my own.

It is thought the size of the 1808 hailstone may, along with a storm in 1697, be the national record for hailstone size - being 20mm greater in diameter than those measured in a Horsham, Surrey, storm in 1958
It is thought the size of the 1808 hailstone may, along with a storm in 1697, be the national record for hailstone size – being 20mm greater in diameter than those measured in a Horsham, West Sussex, storm in 1958

Howard’s report continues: “The most tremendous circumstance of this storm was the destructive hail shower which accompanied its progress.”

The Tornado and Storm Research Organisation (TORRO) grades haistorms from H1-H10, where the hail increases in size from 5-10 to over 125mm in diameter. From the historic descriptions the 1808 storm was an H8/9.This exceeds the British record made during the Horsham, West Sussex, storm of September 5, 1958, which produced hailstones up to 80mm in diameter. Hailstones for the 1808 storm were about 109mm in diameter. Since 1650 there have been 119 independent H5 hailstorms in England and Wales.

Since 1900 there has been a halving in the frequency of recorded destructive hailstorms. Scientists are undecided on whether this is a result of climate change or just a variability of the British weather. But any future uptick in destructive hail should be tempered by this historic record.

It is my belief that people’s current expectations for summer were raised to unrealistic levels when we had a run of warm, dry summers a few years ago. The fact is that because of our maritime climate warm, dry summers occur in this country only occasionally. ‘Default’ summer weather is changeable, rather cloudy and, for many in the north, rather cool

So, if any media outlets do start coming out with any stories of “unprecedented heat” or “worst storm in history” bear in mind that it has probably all happened before.

Scott Whitehead
@wanstead_meteo
http://www.wansteadweather.co.uk

Whatever happened to proper summer thunderstorms?

Is anyone else yearning for a good old-fashioned summer thunderstorm? As we move in to what is traditionally the most thunderstorm-prone month – the Met Office average for this area is three days of thunder – you would be forgiven for thinking that we have plenty to look forward to.

Looking north toward Aldersbrook. The Flats can be very exposed during a thunderstorm
Looking north toward Aldersbrook. Wanstead Flats, a 186 hectare open space that is larger than Hyde Park, can be very exposed during a thunderstorm

It was George II who some time during the 1730s apparently characterised the British summer by saying that it was ‘three fine days and a thunderstorm’.

The reality these days, at least in this part of the country, is quite different. Yes, brief fine spells do still break down – but the classic stormy nights I can remember being kept awake by when I was a lad in the Eighties are now a distant memory. A look back through the records shows that our most thundery month happened in June 1982, when thunder was heard on 13 days. On the 2nd a woman was killed after being struck by lightning while walking in a park in Willesden. More storms followed over the next couple of days and there were three more deaths in the UK caused by lightning. One thunderstorm over Loughton flooded 200 houses, some up to the ground-floor ceiling and at least 12 properties were struck by lightning. One observer recorded 79mm of rain, one and a half times the monthly average, in 90 minutes.

Despite a couple of instances of good potential for thunder this past month has been, so far, completely thunder-free, with all the activity passing well to our east. On June 20-21, there were 235,809 lightning strikes in 24hrs over Germany. To put that into perspective the UK, on a typical ‘thunder day’ in summer, receives up to 10,000 ground strikes although the exceptional day of 24 July 1994 produced 85,000 ground strikes.

The meteo is sited on the Aldersbrook Estate and uploads data to the web every 10 minutes, 24 hours a day
The meteo is sited on the Aldersbrook Estate and uploads data to the web every 10 minutes, 24 hours a day

So what is the potential for thunder in July? Looking back at Wanstead and the surrounding area’s local records the average number of days that thunder was recorded works out as 3.5 – though some years thunder occurred considerably more than others. But to get thunderstorms first we need the ingredients. The classic scenario happens at the end of a short heatwave, a cold front advancing from the west undercuts hot and humid air that has been in occupation for two or three days. If there is sufficient moisture in the upper atmosphere, cumulonimbus clouds will bubble upwards to the base of the stratosphere, and thunderstorms will soon follow.

Apart from the first couple of unsettled days at the beginning of July the above scenario looks unlikely to happen at least in the first half of the month. The North Atlantic Oscillation is predicted to stay positive into July – this spells good news for us as it suggests that the Azores high will dominate our weather, bringing lots of fine and dry conditions. With the jet stream and westerlies being kept just north of Scotland, temperatures should be average to slightly above. It is possible that the high could further dominate as the month goes on. But it is also possible that pressure will start to fall after around the middle of the month. Though it is impossible to predict in detail perhaps a date of around 20th would be the most likely for thunder?

It is too soon to say if the recent trend for a paucity of thunderstorms is just a blip. It could just be another typical variation of the British weather and we will shortly see an upturn in summer thunderstorm activity.

Scott Whitehead
@wanstead_meteo
wansteadweather.co.uk