Adelaide has smashed its average rainfall for February in just one day, after 29 millimetres of rain fell in the city — nearly twice the monthly average of 15.4mm.

The rain fell in just 24 hours from 9:00am on Sunday, as a summer of wet weather continues in South Australia.

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Similar falls were recorded across the state, but in the Mount Lofty Ranges there were falls of between 30 and 40mm.

About 44mm fell at Mount Lofty, accompanied by heavy fog that reduced visibility significantly on Sunday — conditions usually seen during winter.

Bureau of Meteorology senior forecaster Tom Boeck said a rain band moved over the state on Sunday and continued overnight into Monday.

"These sorts of rainfalls are quite unusual for February," he said.

"It does happen from time to time, but to receive rainfall in the order of 15 to 30mm [in Adelaide] or possibly a bit more, is fairly unusual ... and it's likely a similar story for other parts of the state."

The bureau has released a road weather alert for fog and low cloud in the Adelaide Hills.

A downy mildew advice message is also in place for the region, as well as the Mid North, the Riverland, Murraylands and the Upper South East.

Winegrape growers are approaching vintage but a wet summer coupled with humidity and storms has resulted in high levels of maintenance and a likely late start.