# Re: Weather forecasts

On 18/04/2012 20:16, Tim W wrote:
There has been a five day forecast for many years. They used to say that you would never be able to make good forecasts much beyond a few days because of the maths of random systems, it meant that even five days was sometimes very unpredictable. A bit suprised to find a ten day forecast here: http://uk.weather.com/weather/10day-Bristol-UKXX0025
I presume the raw data is always and only generated by the Met Office, so they must be issuing detailed10 day predictions now. are they worth anything?

Tim W

I am looking at the 10 day forecast from uk.weather.com. Each day there is a percentage figure for 'Chance of Precipitation'. Tomorrow for instance we have 70% chance of precipitation and the sense of that seems obvious to me, that the likelihood of some rain tomorrow is 7/10.

For the last day in the period the Chance of precipitation is 0%. What the heck does that mean? That there is zero chance of rain in that 24hr period? Nonsense! Come to think of it if I check tomorrows forecast in more detail I can see that there is virtually no chance that we will have no showers for a whole 24 hrs, so that 70% figure is likely nonsense too, it should be up above 95%.

What on earth are these figures supposed to mean?

Tim W
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