The weekend washout is likely to be at its worst around Sydney, where downpours will begin in coastal regions on Saturday afternoon and up to 25mm is forecast to fall on Sunday alone.

And there will be more freezing temperatures, after many areas experienced their coldest day of the year on Thursday, with the mercury dropping to -4.4C in Canberra, -9.1C in Cooma and 6.1C in Sydney.

Widespread morning frost is expected on Saturday morning over the New South Wales ranges, slopes and western plains and morning fog over the ranges and westerly slopes.

Strong wind warnings are in place along the state’s coastline, with fierce 30km/h winds dropping off on Sunday evening. But there will be no respite to the wet weather until late next week, as the rainfall extends to the ranges.

“A high pressure system over southeastern Australia will shift into the Tasman sea early next week, promoting cold nights inland,” according to the Bureau of Meteorology.

A severe frost warning has been issued for much of Victoria for Saturday morning, with temperatures plummeting to -4C in Mallee, Wimmera and the North East, which can cause significant crop damage.

Alpine areas of Mount Hotham and Fall Creek are expected to see temperatures as low as -6C, while the mercury will plunge to -2C in parts of the Northern Country, North Central and South West forecast districts.

The weather bureau warned temperatures at ground level can be many degrees lower than those recorded by standard weather stations, especially in calm conditions with clear skies.

The BoM warned of showers in Melbourne and persisting over East Gippsland, and fog and frost lasting until Tuesday in the state’s east.

“A large high pressure system over the eastern Great Australian Bight will move slowly eastwards across Tasmania to the western Tasman Sea over the next few days, extending a dry, cool air mass across much of Queensland,” said the Bureau of Meteorology. “Minimum and maximum temperatures will be well below the June average in the interior of the state with widespread morning frost areas in the southern and central interior.

“Early next week, winds along the east coast will trend sufficiently onshore to produce a few showers about the exposed coast.”

A strong wind warning is in place for Gold Coast Waters with 20km/h gusts in Brisbane, light frost and clouds on Sunday. Forecasters predicted possible showers around Fraser Island and eastern Torres Strait on Saturday, spreading inland from the coast south of Bowen on Sunday.

Temperatures in the state are likely to remain below average with morning frost about the southern and central interior and possible rain on the southern coast and northeastern tropical coast. The mercury is expected to be closer to average from Tuesday as moisture increases.

A flood warning is in place for South Australia’s inland rivers, with residents advised to keep away from flowing water.

Saturday and Sunday morning will be cold with severe frost in eastern districts and light to moderate southeast to northeasterly winds. Temperatures will be between 5C and 14C in Adelaide on Saturday, dropping to a chilly 4C on Sunday.

The cold and frost will continue into the week, with the weather warming up slightly by Friday but becoming cloudy, with 25km/h winds tearing through the area.

A gale warning is in place for Western Australia, which is expecting squally thunderstorms and lashing rain this weekend.

“A rain band and cold front will approach the west coast on Friday evening and move across state during the weekend,” said the BoM. “A second cold front will cross the southwest corner of the state on Sunday evening. A ridge of high pressure will develop in the wake of the cold front over central parts of the state during Monday and Tuesday.”

Storms throughout western parts of the Gascoyne and South West Land Division will move through parts of the South West Land Division on Saturday evening, extending over Goldfields, western Pilbara and Eucla on Sunday.

The forecaster warned of damaging winds, heavy rainfall as a strong cold front moves through southwest WA from Saturday afternoon to early Sunday. Sheep graziers were warned of a risk of losses of lambs and sheep exposed to these conditions.

A high pressure system to the west of Tasmania and a low over the Tasman Sea combined to direct a cold south to southwesterly stream over Tasmania on Friday, approaching the coast on Saturday, and moving north of the state late on Sunday.

The BoM warned icy roads will make driving conditions dangerous during Saturday in parts of the Central Plateau, Midlands and Upper Derwent Valley forecast districts.

Residents were warned to expect showers on the west, far south and lower east coast on Saturday, with snow falling above 900 metres during the morning. Sunday will bring potentially severe morning frost, lasting into the week. Temperatures in Hobart will drop from a low of 3C and high of 12C on Saturday to a low of zero degrees on Monday, before climbing slightly again.

The Northern Territory will enjoy the most pleasant weather, with temperatures in Darwin forecast to be between 17C and 30C.

Expect cool and dry conditions moving southeasterly from a high pressure system moving eastwards over southern Australia.

Saturday will bring morning frost south of Barrow Creek and light to moderate east to southeast winds over the Lasseter District. Expect similar condition on Sunday, with morning frost and fresh and gusty winds over the central and southern Districts.

Fire danger is very high in the Northern Fire Protection Area and high elsewhere north of Elliott.