After a cold start to the day, party animals may find themselves huddled around the barbie for warmth rather than sustenance as the mercury splutters to a forecast top of 21.

Australia Day will continue January's below-average chill, with possible showers to top off the cheer.

While not unusual for Victorian festivities, this year follows a scorcher in 2014, which had four consecutive days above 40 degrees during the Australian Open.

"Last year was fairly exceptional," Bureau of Meteorology senior forecaster Rod Dickson said.

This year's tennis fans have replaced sombreros with ponchos as crowd members wrap themselves in picnic blankets during night matches.

2015 has so far failed to break the 40 mark and the chilly spell is set to continue with the temperature to hover in the low to mid 20s for the rest of the month.

But those with good memories know it's un-Australian to whinge too much.

Australia Days in 2013 and 2011 were both cool, recording 21.7 and 21.6 respectively. 2011 didn't have a day over 40 degrees in January and 2012 had just one day over 40.

Cloud is expected to clear throughout the day but Melburnians can expect cool, southerly winds to accompany their afternoon Australia Day celebrations.

Not that any of this will influence a true Aussie's sartorial choice.

As Mr Dickson correctly observes: "It's never too cold for thongs."