BOM changing the weather

I switched over from BOM to Weatherzone (http://www.weatherzone.com.au/act/act/canberra) and haven’t looked back.

I don’t know if BOM does it, but Weatherzone will give you percentage chance of rain as well as the amount expected. For example, it may say 90% chance of rain, but less than 1mm expected. So you know it’s probably going to rain, but not very much.

What’s the deal with the new probabilities?

“Chance of any rainfall:30% Chance of no rainfall:70%”

Are they going to mix other probabilities in such as for example “Chance of any rainfall:30% chance of heavy rainfall:10% Chance of no rainfall:70%”?

Otherwise it seems to add clutter and make the forecast harder to read for no value. (I know they have have some dumb readership but anybody who can understand 30% chance of rain can subtract 30 from 100 surely).

That been said I’ve never really understood the definition of chance of rain and haven’t found a well worded description… Options I have

1) Probability that rain will happen over the AWS in the forecast area. Say Canberra airport.
2) Probability that rain will happen somewhere in the forecast district.
3) Average probability that it will rain at any point in the forecast area.

There are others but I don’t think they make as much sense. For rain these would be very similar but for storms and showers they can be very different.

A couple of years back there was a letter to the editor of the Canberra times bagging out the BoM for forcasting very high probability of rain for a long stretch of days and not having it rain at all. I remember having been rained on during all except one of the days. There wasn’t much rain but it did rain in isolated showers.

I’ll give you a winter prediction.

It’s going to be cold, it’s going to be dark, and it’s going to last for the rest of your life.