As we enter the second week of July most local readers of this blog will not be surprised that we have been in drought conditions for over a month.
There 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, 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.
Looking at the results more closely I’ve divided them into their meteorological seasons.
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.
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.
In 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.
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.
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
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
Total for month 0.7
Wettest day 0.4 day 09
High rain rate 4.0 day 09
Rain days 1
Dry days 29
Highest Gust 18.3 day 14
Average Speed 3.1
Wind Run 2199.7 miles
Gale days 0
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.
Two CET stations, Rothamsted and Pershore recorded 2.2mm and 10mm respectively.
Lewisham’s Beckenham Place Park will next year be home to a new wild swimming lake, thanks to a plan to make London the world’s first National Park City.
The scheme put me in mind of the Shoulder of Mutton lake in Wanstead Park which, decades ago, used to host swimming galas and other events. Long-time residents of Aldersbrook will remember the jetty and diving board that stood at the edge of the lake before falling into disrepair that led to their removal.
With millions set to be spent shoring up the dams of the park’s lake system it is surely feasible that the City of London Corporation can reopen Shoulder of Mutton to swimming while the work is undertaken.
While being cheaper than a lido it would provide an excellent resource and give local residents the chance to enjoy once more swimming in natural surroundings, just like in the Serpentine and Hampstead Ponds.
With the recent warms months of April and May you’d be forgiven for thinking that we’re in for a hot summer. Indeed the recent pattern of weather, would it repeat over the next month, could see many maxima records tumbling.
A look at local east London stats shows that six of the last 10 Junes have been warmer than average while half 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 June.
Probably most notable from the below values is that recent Junes have been devoid of extreme cool temperatures and rainfall.
Snow has been known to fall in June, in 1975.
Rain is usually most frequent in the last week of the month.
The 10 driest Junes were:
Some UK May values according to TORRO
Hottest: 29th 1957: 35.6C at Camden Square, London. Also Southampton 28th 1976
Coldest: 9th 1955: -5.6C at Dalwhinnie, Highland. Also June 1st and 3rd 1962: Santon Downham, Norfolk
Wettest: 28th 1917: 242.8mm at Bruton, Somerset
In terms of climatology June maxima, considering the 1981-2010 average, shows a gradual increase through the month, though around the 19th to the 21st there is often a dip before a warm end. This would reflect the June Monsoon which occurs every year at 77 per cent probability.
The average rainfall graphic reflects this, showing a four-day wetter spell after the 20th.
This May will probably be most remembered for the number of thunderstorms affecting the area. I recorded an unprecedented (in my memory) four consecutive days of thunderstorms.
It was also warm with a couple of days making the top 10 of hottest days since 1959. The mean temperature finished 15.1C, 2C warmer than average, the warmest May for seven years and the 8th= warmest since 1797.
Rainfall at 65.5mm was 128 per cent of average and slightly drier than last year.
Some 244hrs of sunshine were recorded, 134 per cent of average, making it the sunniest May for 7 years, and the 11th sunniest since 1881.
Spring finished with a mean temp of 11C, 0.8C above average, 1C cooler than last year. Rainfall at 181.9mm, was 135 per cent of average, making it the wettest spring for 10 years. Sunshine of only 411.2 hours made it the dullest spring since 2006.
The thundery end to spring has probably built everyone’s hopes up that we’re about to experience a summer with plenty of fireworks in the atmosphere. But the current pattern that brought four consecutive days of thunder (the whole year average is 3.5!) – a continental influence on our weather – could just as easily flip to a mobile south-westerly.
The mean temperature for summer 2018 is looking average overall with average precipitation.
Like the most recent winter forecast I’ve looked in depth at ENSO, QBO and local meteorological data.
The El Niño–Southern Oscillation (ENSO) is a periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean. Current neutral conditions are forecast to continue through to September so any impact is likely to be very small. I had a look at similar years were ENSO was 0.2 in May and came up with the following.
Rather cool: 40%
Average to slightly dry: 60%
Average to slightly wet: 40%
Average to slightly sunnier than average: 60%
Average to slightly dull: 40%
I also had a look the quasi-biennial oscillation (QBO), the quasiperiodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere. This produced only two similar years: 1963 and 2010.
Average to slightly dry: 50%
Average to slightly wet: 50%
Average to slightly sunnier than average: 50% Singularities / patterns
Spring was consistently on the wet side this year with all months at least 127 per cent wetter than average, the total of 182mm made it the wettest for 10 years.
The mean temperature for the spring season, despite the very cold start, ended 0.8C warmer than average, just under a degree colder than last spring which was the second warmest on record.
If you take into account all years back to 1797 that were within +/- 10 per cent of these figures, some 10 ‘best fit’ years emerge.
The list of 10 summers, ranging from 1801 through to 2007, predominantly saw summers that were just on the cooler side of average – no real corkers stand out except for 2001 which saw a hot spell at the end of July that made it into my list of best heatwaves.
As an average this summer could be expressed as: Mean: 17.1C (just below average) Rainfall: 150mm (about average). Sunshine 535 hours (just below average)
Or, expressed in probabilities, I concluded the following:
Temperature Average to slightly below: 50%
Average to slightly above: 20%
Rather cool: 20%
Average to slightly sunny: 30%
Average to slightly dull: 40%
From the above you could deduce that the next three months will be slightly below average for temperature, with average rainfall. And slightly duller than average.
To try to give some idea of what month will have the best weather I’ve broken down the summer into June, July and August probabilities.
Looking at June, after the weekend, the outlook is looking unsettled and gradually turning cooler after the first week. July looks average as does August which, apart from two years, has been a very disappointing summer month.
Perhaps the best weather this summer will be at the end of June and the second week of July – just as most schools break up?
* Taking into account the fact that temperatures in London are up to 0.66C warmer than they were 100 years ago I have added 0.66C to mean temperatures before 1915.
** Obviously, in the event of a series of direct hits from thunderstorms, my rainfall estimate could be hopelessly short – a symptom of abundant solar energy at this time of year which creates a ‘noisy’ atmosphere compared with winter.
*** The 1981-2010 average mean for summer in this region is 17.6C, with 144.9mm of rain and 564 hours of sunshine
Posts about thunderstorms are usually few and far between – the average number of thunderstorms in this part of the UK in a summer month (July) is just 3.5.
So experiencing four in four days must be very rare; the record for thunderstorms in a month is 12 in June 1982 though I’ve no idea how many of these were on consecutive days.
While the storms over the weekend were all about lightning this one was all about rain and loud thunder. Tuesday, May 29th, started cloudy and dull with some light rain. I was expecting some rain but it lingered and became heavier at 11.30am before turning torrential at 1pm, going against forecasts from BBC and Met Office – the trough was a lot further north than modelled. I pointed this out to the UKMO to be told that a yellow warning was in place for the whole SE region.
Some 26.5mm fell in just over two hours bringing lots of surface water and flash floods around Leyton and Walthamstow. At 1pm, while driving in this area, a bright flash was quickly followed by cannon-like thunder. A further fall in the early hours brought the 09-09 total rainfall to 29.8mm, the 5th greatest May fall since 1959.
The coming bank holiday weekend is looking very warm, possibly hot on Monday. And with the heat comes the inevitable thunderstorms.
Looking at the CAPE forecast on @wxcharts the risk on Saturday looks like staying to the west of London. The best chance for east London looks like after noon on Sunday and Monday. There is no guarantee of thunderstorms here – some places could get hammered while just down the road it could stay dry – the potential is there.
Meteorologists will be keeping a close eye on Herstmonceux and Trappes ascents in the coming days.
Weather models are hinting that this coming bank holiday weekend could be very warm indeed, with one WX Charts animation suggesting that a positive anomaly of 12C could be possible on Monday.
A date record looks a formality and, unless there’s a downgrade, new monthly high temperature records at stations across the south-east look a possibility.
While it looks very warm it is too early to start talking about heatwaves. And, considering the pattern since late February, with hot and cold alternating weekly, a brief return to much cooler conditions at the beginning of June can’t be ruled out.
The British record high temperature for May is 32.8C, reached on two occasions:
Camden Square, London May 22nd 1922. The same station recorded this value again on May 29th 1944, along with Regents Park, Horsham and Tunbridge Wells.
The national date record for the 28th, according to TORRO, is 30.6C at Camden Square.
Locally the highest temperature recorded in this area in May is 32.1C on May 27th 2005. The date record I recorded is 26.5C in 2012.