As Melbourne breaks records on Wednesday for warm spring weather, we are being asked to brace ourselves for "extreme" rain to hit on Friday.
The city is forecast to be lashed with more than its monthly December rainfall average in just the first two days of summer.
Meanwhile, some areas of the state are expected to cop up to 250 millimetres.
"It's certainly going to be a very wet start to summer," Bureau of Meteorology senior forecaster Richard Carlyon said.
Hot weather in #Melbourne sets a new record of 13 days over 30 degrees prior to Summer, beating the previous record of 12 days in 2009. 35 degrees forecast today, but don't tell #Brisbane@BOM_Qld.....they haven't had one 30 degree day this November! https://t.co/VQTDMcLcODpic.twitter.com/dSp3GpNZ9R??? Bureau of Meteorology, Victoria (@BOM_Vic) November 28, 2017
The bureau will release a severe weather warning Wednesday afternoon regarding the slow-moving trough.
Northern Victoria will bear the brunt, with up to 200 millimetres expected to fall in areas. The North-Eastern ranges is likely cop up to 250 millimetres.
Melbourne is forecast to receive up to 50 millimetres of rain on both Friday and Saturday, almost double December's entire average of 60 millimetres.
Mr Carlyon said rain levels could rise quickly and a flash flood warning was likely for the entire state.
#VICStorms outlook for today. Severe thunderstorms possible in western #Victoria this afternoon with large hail and heavy rain the main threats. Thunderstorms also possible over the Eastern Ranges. Keep an eye out for warnings: https://t.co/ap6V1hCrbEpic.twitter.com/wUsCPwbijM??? Bureau of Meteorology, Victoria (@BOM_Vic) November 29, 2017
The humid spring weather has led to a build of moisture in the air, paving the way for the heavy rain.
Wednesday's scorcher is the 13th day that has topped 30 degrees before summer arrives in Melbourne.
At 1.30pm the mercury had hit 34, with a predicted high of 35.
It breaks the previous record of 12 pre-summer days above 30 degrees in 2009.
The story Flash flood warning to follow scorching spring weather first appeared on The Sydney Morning Herald.