There's a crystal ball seller on ebay - try them prob as accurate as BOM beyond 5 days - watch the SBS show "maths" theres an episode on computer generated weather - the example of multiple forecasts - they were all over the place until 3 days when they then closely aligned
At 7 days just choose the forecast from all the sites that is the furthest from what you need and youll probs be about right - and youll get a few surprises along the way