The Victorian health department says there is a moderate risk for thunderstorm asthma.

Wind, rain and thunderstorms: wild afternoon forecast for Melbourne

It will be a wild and woolly afternoon in Melbourne, with a severe weather warning for damaging winds issued by the bureau for most of southern Victoria.

Damaging winds are averaging 50km/h to 60 km/h, while gusts of 90km to 100 km/h are expected across southern and mountain areas.

The bureau is also predicting thunderstorms, most likely in the eastern suburbs, before a cool change is expected to lower temperatures about 4pm.

Some airlines are also urging passengers to check flights out of Melbourne airport, with strong winds likely to ground flights.

"At the moment we have showers and storms to our west. They will move through this morning and we will see further shower and storm activity during the afternoon," said BOM senior forecaster Michael Efron.

"However, as the cool change moves through, that activity will be contracting east and clearing."

"Early evening, we might actually see dry conditions for Melbourne, so if you're heading out, your Friday night is looking pretty good."

A total fire ban has been issued for the Mallee in Victoria's north west for Friday.

'Exceptionally warm': Melbourne records warmest night since January

Friday's wild weather comes after Melbourne sweltered through its warmest night since January, with an overnight low of 23.6 degrees at 6.15am.

It was even warmer in the hours prior, dropping only slightly to 29 degrees at 10.30pm and then 27 degrees at 3.30am.

"It was exceptionally warm for an overnight low," said Mr Efron.

"For a maximum, we average 22 degrees in November. That highlights how warm it has been."

It was the warmest night since January 29 this year, when overnight temperatures did not dip below 28 degrees.

The temperature only started to fall about 6am, after Melburnians tossed and turned through temperatures in the high 20s for most of the night.

"With that hot day yesterday, we saw the continuation of northerly winds overnight and cloud cover acted as a blanket, trapping that warm air across the state," said Mr Efron.

Melbourne sweltered through its hottest day since March on Thursday with the temperature soaring above 30 degrees for the first time in more than seven months.

Saturday's Derby Day is expected to be dry, and partly cloudy, with light winds and a top of 19 degrees.

But Mr Efron warned Melbourne Cup day may not be as pleasant.

"At this stage we see another change moving through so I think we will see some showers around and even the risk of a thunderstorm [on Cup day]. It is looking like we will have a change through that day, there is some rainfall expected and southwesterly winds developing as well."

Getting out of the city for the long weekend? Here are some forecasts

LORNE: Mild weekend, partly cloudy with a top of 17 on Saturday and 22 on Sunday, before possible showers on Monday and Tuesday.

WILSONS PROMONTORY: Cool weekend, with a top of 15 on both Saturday and Sunday, with a chance of light showers and light winds. High chance of rain on Monday and Tuesday.

DAYLESFORD: Mild and dry day on Saturday with a top of 16, before it warms up to 22 on Sunday. Monday will be cloudy with a top of 25 degrees and a high chance of afternoon showers, before it cools to 17 on Tuesday.

MORNINGTON: Top of 18 on Saturday and 22 on Sunday, partly cloudy with only a small chance of showers. It will be hot on Monday, with a top of 27 and high chance of showers, before a top of 20 on Tuesday.

PORT FAIRY: Mild weekend, partly cloudy with a top of 17 on Saturday and 20 on Sunday, before possible showers on Monday and Tuesday.

HALLS GAP: Top of 15 on Saturday before it warms to a top of 21 on Sunday and 22 degrees on Monday. Rain likely on Monday before it cools to 16 on Tuesday.