SA braces for widespread rain and storms

South Australia is bracing for thunderstorms, heavy rain and possible flash flooding in some areas as a low pressure trough moves across the state.

The Bureau of Meteorology has forecast widespread rain on Wednesday with parts of the mid-north to get around 50mm and up to 15mm to fall across Adelaide.

The rain will be heaviest in the late morning or afternoon.

The forecast conditions have prompted the State Emergency Service to urge property owners to prepare for possible damage and for all people to be wary of flash flooding.

"Our advice is to never drive, ride or walk through floodwater. It can only take a few centimetres of fast-flowing water to sweep a car away," SES state duty officer Sara Pulford said.