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

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3 responses to “Whatever happened to proper summer thunderstorms?

    • Before last July thunder events were much rarer than previously. There were six thunder events last July though most were just a rumble or two of distant thunder – nothing like the events of 1982 and other years of that decade. From the publications I have read the current situation is at odds with what the Intergovernmental Panel of Climate Change told us to expect in terms of hotter, drier summers broken down by intense thunderstorms. Instead we have had a run of relatively cool, wet summers with few intense storms. It could just be a natural variation of our climate and just bad / good luck, depending on you view, that we have had a calm run without storms.
      Another factor to consider is that the incidents of thunder in Scotland has increased the last few years. Is this a result of the buckling jet stream? The near miss of earlier this month, when the models said thunder was a fairly sure thing, makes it more intriguing. There is a lot we still have to learn about the behaviour of the development of thunderstorms

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      • Many thanks for this… v interesting stuff, esp Scotland’s increase in Ts activity: higher latitudes generally get less Ts due to thinner troposphere (?). Reykjavik has little thunder recorded, for example, but has experienced more in recent years, even as early as April. Pinning down Ts seems fraught with difficulty: the high CAPES and low Lifted Index forecast on 48hr runs during the warm plume earlier this month simply dissolved into nothing on the 00Z runs on the day (if u see what I mean!). Thanks again, v informative.

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