On a Saturday closest to full moon in July thousands of cyclists congregate in London Fields and ride 200km through the night to Dunwich on the coast of Suffolk.

Modestly described by the organisers as a “gentle bike ride to the beach, through soft country on good roads” the hours of darkness present a huge challenge for participants.

Michael Barry, the retired Canadian professional road racing cyclist, rated the challenge 5/10, harder than the 280 mile London to Paris ride which he ranked only 2/10.

Taking place in summer you would expect long hours of moonlight to be a welcome assist for these brave souls who peddle hours through the night to reach their goal. A look at the synoptic charts and statistics of each ride, however, reveals weather that is often a long way from being summery.

Looking in detail there appears to be very little chance of the ride coinciding with a heatwave. In 1999, 2003, 2004 and 2014 riders left the capital during days where the mercury reached above 80F (26.7C) – though this represents only 17% of starts. Temperatures around 70F (21.1C) are much more common.

Over 40% of the rides have seen over 1mm of rain on the opening day, this falls to 17% on the second day – a dry end to the marathon challenge is perhaps to be expected.

Patrick Field, of the London School of Cycling, said that 2007, the wettest start day to a Dynamo, was “gloriously wet”.

Perhaps what this blog also reveals is that UK weather at full moon, even in high summer, is notoriously unpredictable. Luke Howard , the father of meteorology, tried for 50 years to
prove a link between the weather and phases of the moon, but died still mystified at the ripe old age of 91.

A movie of all synoptic charts highlights just how unsettled this time of year can be found here.

* The author is planning to take part in this year’s event to raise money for Cancer Research.

** Full stats for the weather in London during the Dunwich Dynamo back to 1992 can be found here: https://onedrive.live.com/redir?resid=A148835276FAFDEE!2561&authkey=!AEMmoeUZRVSq7uU&ithint=file%2cxlsx