It comes from listening to the ABC radio and the quote of 70%...

It comes from listening to the ABC radio and the quote of 70% ish accuracy out to 12 hours was made by a bloke who worked for the BoM.

By the way, the accuracy going out further than 200 kms from the collection point does drop down.

If you think that my quote is bulltish, go check the google and see what it suggests is the accuracy of weather forecasts.

Or keep your head in your back passage and believe that the weather forecasters are incapable of making a mistake.