Victorians have been advised to keep umbrellas handy on Tuesday because of forecasts of rain, possible storms and flash flooding late in the day.
For Melbourne, Monday's mid-afternoon maximum temperature was 32 degrees. Crowds enjoyed warm and sunny conditions at the Moomba march. Clouds converged later in the day, but there was little rain.
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Thunderstorms ahead for Melbourne
Melbourne will experience the odd shower tonight before a hot day tomorrow ahead of evening thunderstorms.
The Bureau of Meteorology expected a late afternoon a change from 35km/h northerly winds to up to 25km/h south-westerly winds, with a 30 per cent chance of light rain.
Conditions might deteriorate on Tuesday, and thunderstorms may develop.
After an overnight low of 21, Tuesday's top temperature is forecast to be 34 degrees. The bureau expects isolated showers in the late afternoon, increasing to areas of rain and the chance of thunderstorms on Tuesday night.
Winds are expected to increase from north-easterlies of up to 25km/h to north-westerlies of up to 40km/h.
Bureau forecaster Peter Newham said the risk of storms on Monday in Victoria was "quite low" and only 1mm or 2mm or rain was expected.
"There hasn't been any storms yet today, fairly weak showers coming over the Melbourne area at the moment, and there's some bigger showers on the ranges east of Mount Hotham but they haven't produced lightning yet that we've seen," he said.
There was a bigger risk of storms on Tuesday, particularly mountain and southern areas, including Melbourne.
Later in the afternoon and evening, there was the potential for 5mm to 10mm of rain and storms.
The commercial forecaster Weatherzone predicted severe thunderstorms as a front and trough swept across Victoria on Tuesday.
"Storms will become more widespread in the afternoon with some storms potentially producing frequent lightning and damaging winds," Weatherzone said.
"In the evening the air mass is likely to become more saturated leading to areas of rain across the state, with some thunder and lightning mixed in. There should still be a few more significant thunderstorm cells bringing the risk of damaging winds and flash flooding.
"All of the Melbourne and almost all of Victoria will at least get some rain in the evening or overnight, but rainfall totals should only exceed 15mm with thunderstorms."
Mr Newham, of the Bureau of Meteorology, stressed: "It's not a clear cut situation where we're going to get severe storms. it's definitely a chance; there's much more instability tomorrow.
"If they occur, probably flash flooding would be the biggest risk." Mr Newham said it was possible there could be "heavy rainfall and large hail if the storms develop big enough, or damaging wind gusts – they're a lower risk but they're still possible".
"It's a long way from occurring with any certainly anywhere in Victoria, it's just a chance. It's just a bit more unstable tomorrow," he said.
"The whole of Victoria is a risk of storms tomorrow, and it's probably more likely in the southern areas and over the dividing range. There's no clear signals that they'll be severe anywhere in particularly. It's just a risk and one we'll have to monitor."
On Wednesday, the Melbourne forecast is for an early shower or two and a top temperature of 21.
Weatherzone predicted a wet Australian Grand Prix at Albert Park in Melbourne.
"On the grand prix weekend a strong cold front will surge across the state bringing rain with gusty cold winds, particularly on Sunday," Weatherzone said.