Melbourne is on the cusp of the coldest December day since 2006 - less than two weeks after boiling through the equal-hottest November day this century.

The city hit a maximum of 16.8 degrees on Sunday, but is forecast for only 15 on Monday, as a series of cold fronts continues to push frigid air from the Southern Ocean.

If the prediction pans out, it'll be the coldest December day since Christmas Day in 2006, when it peaked at 14.5 degrees and actually snowed.