On Tue, 24 Feb 2004 10:47:06 -0000, "Dave L"
wrote:

50% chance of rain
50% chance of snow/snip

I think you'll find that the warning is of 50% risk disruption due to
severe weather, heavy snow in this case. It's not saying that there is a
50% risk of snow. Maybe you should you read the explanation behind the
warning i.e 'Snow falling at a rate of approx. 2 cm/hour or more
expected for at least two hours' before dismissing it so lightly.
If it were the case of just a snow forecast, the percentages would be
much greater.

Actually Dave I was being a bit more general. My comments were aimed
at various weather forecasts available to the general public which do
indeed state things like "50% chance of rain".

However, there's still the point that 50% risk of disruption means
"there could be disruption, but it might not happen". For someone that
doesn't want disruption that's a bad thing. For someone hoping for a
day off work it's a good thing.

I'm not saying that percentage indicators are a bad thing so long as
they are interpreted correctly.

It's all a matter of perspective. From the 0% perspective, 50%
probability is pretty good odds that it's going to happen. However,
from the 100% perspective 50% probability is pretty good odds that
it's not.

In reality, a balanced view can only be made if the relative
probabilities are assessed from the 50% point. In other words, it's
likely that it will rain today or it's unlikely that it's going to
rain today. The 50% point then becomes the origin of measurement.
The zero confidence or "don't know" point ;-)

--
Pete Lawrence
http://www.pbl33.co.uk
Home of the Lunar Parallax Demonstration Project