The 'City to Surf' is the world's largest running race and the 80,000 competitors should be prepared for some damp weather as they make their way from the CBD to Bondi on Sunday morning. Showers are forecast to develop during Saturday night and will remain a significant risk through Sunday morning. Weatherzone's 3-hourly forecast data indicates a 50% chance of showers at 9am, when many will be heading towards the steep slope of 'heartbreak hill'. On Sunday morning, a cold pool of air in the mid to upper levels of the atmosphere will be tracking across eastern NSW, creating unstable and cloudy conditions over Sydney. Light to moderate southeast winds will also carry a fairly humid airmass across Sydney from the Tasman Sea, boosting the chances of rainfall during the run. 5-10mm of rain is likely over Sydney during Sunday and there could be the occasional heavy downpour during the run. The temperature through the race will be on the cool side, increasing from 11 to 14 degrees during the morning, although this is pretty typical for this time of year.