The Glastonbury Festival takes place between June 21st and 25th. It occupies a unique place in the calendar and is arguably the most loved of the music festivals which take place each year in the UK. Due to a combination of a) it taking place early in the summer and b) being such a massive event, there is always a great deal of interest in the weather. It's important to remember that in the UK forecasting even a few days ahead can be prone to significant error, so at longer ranges the key is to look at trends and probabilities.
The first half of the meteorological summer is sometimes referred to as the European Monsoon or "return of the westerlies". In late spring there is a tendency for the flow of westerly winds to weaken across the UK, but in June and July they strengthen and bring an increased likelihood of more unsettled weather. In other words the chance of rain may increase and in the past Glastonbury has been no stranger to mud and rain!
By Domharrison (Own work) [Public domain], via Wikimedia Commons
Medium range computer models forecasting between 16 and 30 days ahead point towards drier than average weather continuing for much of May. Will things change as we head into June and the European Monsoon season?
It is far too early to be confident. Seasonal computer models are suggesting the likelihood of above average temperatures during June, but the rainfall signal is more varied. The Climate Forecast System (CFS) v2 which is run by NCEP in the USA has been one of the models suggesting positive 500hPa anomalies over the UK in June. This means an increased chance of high pressure, which in turn leads to settled and (in the summer) warm periods. The CFS v2 500hPa anomaly chart below is for June 2017 and is generated using data from Friday 28th April. Yellow shading indicates a positive anomaly and blue a negative one.
As well as the CFS v2 several other seasonal computer models suggest a drier than average June. If correct, wet spells could still be expected at times, but the chances of the Glastonbury Festival coinciding with a fine and sunny weather would be higher than normal.
Unfortunately the last update of the Met Office GloSea seasonal model suggests something different. It has a weakish signal for above average rainfall levels during the June, July and August period taken as a whole. Less good.
This article will be periodically updated during the run up to Glasto 2017. It is much too early to consider the weather forecast details, but some pointers are emerging. These are:
1) There is a signal for above average temperatures in June. This doesn't preclude colder intervals, but it means an increased chance of warm weather during the festival
2) The rainfall signal is mixed. A number of seasonal computer models favour drier than average conditions, but the last run of the UK Met Office GloSea contains a weak signal for above average rainfall during the June, July and August period taken as a whole
On the basis of the current data we consider the outlook for Glastonbury 2017 to be quite promising.
The forecast link below updates every day and runs from 30 to 150 days ahead. Its value is in looking for trends rather than details
Day 30 to 150 south England weather forecast
The forecast link below updates every day and runs from 16 to 30 days ahead.
Day 16 to 30 south England weather forecast
The forecasts below are updated every 6 hours and go out to 16 days ahead.
16 day Glastonbury weather forecast
16 day Glastonbury weather forecast (format best for smartphones)
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