Sydneysiders will be reaching for an extra blanket on Sunday as temperatures tick down to 12 degrees, marking the coldest morning of the year so far - and possibly the coldest March reading in 15 years.

Sunday morning will signal a real autumn chill, with the 12-degree reading about 7 degrees cooler than Sydneysiders have been used to so far this month. It would also come in about 5 degrees lower than the long-run average for the month.

Sydney is set for the coldest March morning in 15 years. Credit:Janie Barrett

The Sunday cooling will follow a Saturday when many people will already be looking to hunker down, as rains of as much as 25 millimetres, including a possible storm, return. Winds reaching 45 km/h will also make temperatures feel less than the forecast top of 26 degrees on Saturday.

Lest beachgoers think summer's done, a return to sunnier conditions by midweek will see the mercury climb back into the mid- to high-20s across the city.