Australia’s eastern states are preparing for four seasons in one week as a heatwave and thunderstorms with heavy rain and possible flooding are forecast as spring turned typically unpredictable.

The storm that drenched parts of Victoria late on Sunday moved across the state on Monday as forecasters warn of heatwave conditions in South Australia later in the week.

In NSW, large swathes of the southern, southwestern and western parts of the state were bracing for severe thunderstorms amid a low pressure system.

Damaging winds and large hailstones were on Monday forecast for areas stretching from Cooma in the south to Wilcannia in the far west, with the system then pushed northeast by a cool evening southerly.

Greater Sydney could also experience thunderstorms over the course of Monday night but they would likely subside around 8pm.

“As that change moves through, that’s really triggering that thunderstorm activity and also those warm conditions ahead of that change,” Bureau of Meteorology NSW manager Agata Imielska said.

Meanwhile, the Victorian Bureau of Meteorology recorded 24-hour rainfall totals of up to 65.6 millimetres at Mount Donna Buang while Moorabbin in the south-eastern suburbs of Melbourne had its wettest November day with 63.2 millimetres.

The bureau recorded almost 300,000 lightning strikes across the state. There was also heavy rainfall and damaging winds.

In one instance, a 70-year-old woman was taken to hospital after being blown off her feet at Yarrawonga Holiday Park.

Heavy rain remains a possibility in the east of the state and a severe weather warning remains in place.

Tweet from @BOM_Vic

And in South Australia, a significant change from the wet conditions to a heatwave is forecast with temperatures expected to rise later in the week.

Adelaide is forecast to reach 38 degrees on Friday and 40 on Saturday.

Melbourne is forecast to reach 31 on Friday and 34 on Saturday. Sydney won’t escape the heat either, reaching into the low-30s on both days.

Victoria’s SES said on Monday morning it had 385 calls for help in the previous 24 hours, including 170 from greater Melbourne, due to flash flooding.

Crews in central Victoria had their work cut out for them after a “rather large” tree with a diameter of 1.5 metres smashed across the Goulburn Highway earlier on Monday.

Tweet from @vicsesnews

Strong winds in and around Ballarat on Monday morning also meant one building lost its roof.

Fire threatens in NSW northern regions

NSW northern districts are facing an elevated fire threat amid hot and windy Monday afternoon conditions. The Far North Coast and North Western regions are exposed to “severe” fire danger.

A fire in the Glenugie state forest, 18km southwest of Grafton, was on Monday elevated to “watch and act” level after burning out of control.

The Rural Fire Service is sending additional aircraft to fight the blaze.

Monday’s cool southerly may also trigger thunderstorms as it passes over the state’s northeast, Ms Imielska said. She recommended those in the northwest and northeast keep an eye on fire conditions.

Difficult fire conditions could then return from Thursday to Sunday as a fresh heatwave rolls across the state, particularly western NSW.

-with AAP