There's not too much change from Jo's forecast yesterday, though there is less cloud now expected at first and the wind has added a couple of miles per hour after midday.
With the breeze coming from the west, runners will be hitting a light headwind for the last 6 miles or so, as well as the first half of the event - and any one in fancy dress might welcome a bit of a breeze, as temperatures will climb to 16-17c in the afternoon, and with enough of sunshine to keep spectators reaching for the sun cream. With little humidity to worry about and low air pollution the elite runners will be hoping to set a fast time, and other runners will be glad of the westerly flow bringing cleaner air compared to last week.
You can check
London Marathon forecast details here