History and Predictions for Glastonbury Festival Weather

History and Predictions for Glastonbury Festival Weather

by john / Jun 10, 2015 / 3 comments
Friday, 26 June 2015 to Sunday, 28 June 2015

With long range weather forecasts too shakey for confidence, Festivals and Gigs decided to do some math and figure out the likelihood of good weather at Glastonbury Festival.

Weather can have a big effect on the Glastonbury experience and if bad weather is likely, then luck favours the well-prepared when it comes to enjoyment factor. 2015 will be the 33rd Glastonbury Festival and marks 45 years since the first event was held on the 19 September 1970. The weather was good that day with a high temperature of 21.3°C. From that year forth the festival was moved to coincide with the weekend following the summer solstice. Given Britain's tenuous climate for June, the weather became more unpredictable.

So let's figure out some probabilities:
There have been 15 years where the festival remained free of mud, although only 8 years where there has been no rain on the site during the festival. The sunshine years with no recorded rain are 1970, 1983, 1989, 1992, 1993, 1995, 2000 and 2010. The last sunny year in 2010 saw the highest total number of hours of sunshine in the festivals history with virtually cloudless skies throughout. The highest temperature was recorded in 1984 at over 27°C and the highest average temperature was experienced by the lucky festival goers of 1989.

Between 1983 and 1995 there was only 1 muddy year in 1985, but that year was an epic mudbath.

Of the 17 muddy years, only 10 years were so bad that we are categorising them as epic mudbaths. These years were 1982, 1985, 1997, 1998, 2004, 2005, 2007, 2009, 2011 and 2013. By far the muddiest and wettest years in the festivals history were 1985, 1997, 2005 and 2007. Lightning strikes shut down several stages in 2014, however Friday night of 2005 saw the most immense storm to hit the site with several stages struck by lightning and flash flooding enveloped the lower slopes of the Pennard Hill Ground leaving thousands of festival goers as tentless refugees. Significant improvements were made to the sites drainage over the next 2 years which prevented flooding in 2007, but persistent rain throughout the weekend brought the worst mud in the festivals history and no sunshine was recorded in Pilton for the whole of June of that year. We shiver at the mere memory.

In recent years the weather has been relatively poor, where during the last 10 year history of the festival back to 2004, at 9 festivals there was significant mud, and 6 out of the 9 festivals were epic mudbaths. This means 31% of all Glastonbury Festivals have been epic mudbaths. 53% of the last 15 festivals, 6 out of the last 10 years. That means it's getting worse.

No weather sites are currently providing forecasts as far out as the festival, however, following false reports of good weather on the horizon for June, it's looking increasing likely that the coming weeks will bring heavy rain and lightning to Pilton. With luck however, we could see the bad weather burn out in time for the festival.

Let's examine the odds of favourability. The Sunshine Years occur in spurts, popping up every 5 years or so. It's been exactly 5 years since we've seen such a festival, so it seems we are due. Yet a purely statistical approach reveals the likelihood of a hot, dry Glastonbury is a mere 20%.

Based on the historic trends and averages and current short term forecasts, we are predicting a 45% chance of an epic mudbath, a 20% chance of a sun-soaked festival, and a 35% chance of a moderately muddy yet tolerable British climate. If we were packing today, we would be certain to pack wellys and wet weather gear just in case.

Here is a spreadsheet documenting the historical weather findings and other interesting statistics. Click to enlarge in a new tab.
Glastonbury History Weather Spreadsheet

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