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The 2018 Virgin Money London Marathon takes place on Sunday 22nd April. The London Marathon was first run in 1981 and has since grown to become the third largest running event in the UK, after the Great North Run and the Great Manchester Run. Last year over 40,000 runners started the event.
The weather conditions on the day can have a big impact on performance. Research suggests the performance of runners in marathons decreases as the wet bulb temperatures increase from 5C to 25C. Higher wet bulb temperatures indicate more humid air.
What's the London Marathon weather forecast looking like this year?
By Chmee2 (Own work) [CC BY-SA 3.0], via Wikimedia Commons
Computer models are currently favouring:
1) Warm or even very warm conditions.
2) Dry conditions early on but an increasing risk of showers developing as the day progresses.
The GFS12z chart below shows forecast rainfall for 12:00GMT on Sunday 22nd April. Showers are breaking out in central and eastern England but they could be localised and there would be a reasonably good chance of it remaining dry for the London Marathon.
The chart below shows the maximum forecast temperatures at the same time. In the London area values have already reached 25C (77F) and it would still be getting warmer at that time of the day. This projection from the GFS12z is at the top end of the possible outcomes with other models pointing towards somewhat cooler conditions.
At this stage the likelihood is the London Marathon will be run in warm weather. There is a possibility of it becoming very warm, and high temperatures have the potential to cause problems. The risk of heavy showers increases through the day but it may well stay dry for the marathon.
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