Sydney has capped off a mostly mild autumn with a cold snap that made it feel like winter had landed a tad early.

The city shivered through its coolest May morning in 18 years on Monday and Tuesday's top of 16.3 degrees was the chilliest since last August. Taking wind chill into account, the day's apparent temperature barely scrapped above 10 degrees - at 1 pm.

It's that time of year: cold snap to end May and autumn for Sydney. Credit:Nick Moir

The drop in temperatures will drag on the monthly averages but May will still emerge just shy of two degrees above average for the month.

"We've had high-pressure systems dominate Australia for long periods of time, particularly in eastern Australia," Rob Sharpe, a meteorologist with Weatherzone, said.