UPDATE 3.30PM: Toowoomba is in for a much-needed bucketing of rain this weekend.
Bureau of Meteorology meteorologist Andrew Bufalino said only patchy falls were expected tomorrow but a rain band could bring between 20 and 50mm on Sunday.
However if thunderstorms hit on Sunday, up to 100mm could fall.
According to the bureau, a surface trough and an upper trough will combine to cause moderate to heavy rain across eastern Queensland, extending to Victoria.
Rainfall on Sunday was expected to peak in the afternoon.
An east-coast low could develop in NSW but that was unlikely to affect Queensland.
Mr Bufalino said the bureau would issue flood warnings when required.
"Residents should watch for any flood warnings and in particular thunderstorm warnings.
"The heaviest rainfall will be associated with thunderstorm activity."
On Monday the bureau is expecting the system to move off the coast.
Some cloud cover and shower activity will persist but mostly in the Western Darling Downs and Granite Belt regions.
In Toowoomba it is expected to be cloudy and gusty with cool, westerly winds.
The maximum temperature will reach 21 degrees today and just 15 degrees tomorrow.
It will remain cool for the start of next week when it will be mostly sunny although there is a small chance of rain.
UPDATE 10.30AM: Bureau of Meteorology acting Queensland regional director Richard Wardle said to expect flash flooding in some areas this weekend, and prepare for rivers and creeks to rise.
"Rainfall and gusty storms are expected throughout the weekend," Mr Wardle said.
"These storms may be severe, particularly close to the trough, and we urge the public to stay tuned for warnings and local media updates over the weekend.
"While there is the potential for another East Coast Low to develop off the NSW coast as the system moves further south, this will not have an impact on Queensland.
"The impacts of coastal erosion are unlikely to be as significant as early June, due to generally lower tides and swells," said Dr Wardle.
Western parts of Queensland will cop the first rainfall from the trough, but the BOM expects it will move and expand to affect much of southern Queensland, with some rain expected as far north as Townsville.
Isolated falls of more than 100mm are possible with thunderstorms.
Queensland Fire and Emergency Services Deputy Commissioner Mike Wassing said it was time to think about whether you really need to be on the roads this weekend.
"If you do, make sure you have a Plan B in place, including identifying alternative routes. Flooded roads are dangerous and unpredictable, and the message is simple: if it's flooded, forget it," he said.
7.30AM: A flood watch has been issued with authorities warning up to 90mm could fall in Toowoomba this weekend before a cold blast hits.
Heavy rain is expected to settle over the Darling Downs on Saturday afternoon and continue Sunday.
An initial flood watch warning has been issued by the Bureau of Meteorology warning of in excess of 100mm in parts of southern Queensland.
South Brisbane Storms is forecasting severe thunderstorms throughout Sunday.
The wet weather should clear by Monday afternoon before a cold blast hits the region.
Temperatures could get to as low as 7 degrees in Toowoomba and 4 degrees in Oakey.
Forecasts are predicting it to get as slow as 2 degrees in Stanthorpe early in the week.
An upper trough is driving the weather system and will combine with a low surface trough to bring rain.
The system will move from west to east, drawing on moisture from the tropics.
Bureau of Meteorology forecaster Sean Fitzgerald said weather events like the one forecast were hard to predict and could change quickly.
He said the bureau would continue to update its forecasts.
"Readers should keep an eye out for warnings, particularly flood warnings," he said.
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