What’s a 50% chance of rain?

According to weather forecasts across Japan this evening, tomorrow there will be a 50% chance of rain. Whoopie-do! What’s that supposed to mean? Should I take an umbrella? Should I hang out my laundry? I don’t know, and neither do the students I asked.

Believe it or not, I was once asked to leave a bar in Nagoya because I got into a ‘heated debate’ about how meaningless the Japanese kousuikakuritsu figures are. Kousuikakuritsu means ‘the chance of rain’, and I just can’t understand the point of it. All we need to know is whether or not it’s going to rain, right? Surely the weather forecasters are paid to tell us exactly that. I mean, anyone can look at the sky and say it ‘might’ rain.

One thing you’ll notice in the summer months, despite weeks of dryness, is how they almost always state that there’s a ten percent chance of rain… just so they can’t be wrong!

To be honest, it’s not so much the sillyness of such figures that bugs me, but more the fact that no-one else can see how silly they are! Am I really alone here? Someone, anyone, please agree with me before this drives me insane!

If you like, you can find me on Twitter at @nick_ramsay. I'd love to hear from you!

3 thoughts on “What’s a 50% chance of rain?

  1. You’re not alone !

    When I first learnt of the kousuikakuritsu figures not so long ago, I researched what they were supposed to be exactly (I am still a meagre student of the Japanese language and it’s culture) so it was all new to me.

    Low and behold I found it nigh impossible to figure out how exactly the figure is created let alone how a poor gaijin like me is supposed to know what to make of it.

    If you want my advice, toss a coin then at least you can blame the coin!

  2. This is interesting, you don’t have “chance of parcipitation’ ratings in the UK? Very common here in Canada. I know that when the report says- 75% COP, I know that theres a damned good chance I’m either going to get rained on or snowed on (depending on the season). Better carry and umbrella. If it says 10% COP, I won’t carry anything but understand that it just might happen. I guess we grew up with it and thus understand it.


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