On Sat, 11 Jun 2011 14:19:26 +0200, Gavino wrote:

"Adam Lea" wrote in message
...
On 11/06/11 09:00, Gavino wrote:
But the real lesson is that anyone who predicts the weather several
weeks
ahead is never 'right' or 'wrong', merely 'lucky' or 'unlucky'.

If someone wins the football pools, no-one would think to praise him
for being a great forecaster.
Why should (long-range) weather forecasting be any different?

Because seasonal forecasting is conducted using physical/dynamical
relationships within the atmosphere, not guesswork. It is possible for
some seaonal forecasts to show skill when assessed over many forecasts.

OK, I was stretching the analogy a bit to make the point. With some
specialist knowledge, you can shorten the odds against you, just as a
seasoned stock-market analyst might occasionally come up with a good
tip.

But ultimately the chaotic nature of the underlying dynamics puts a
limit on how far out you can forecast with any degree of confidence. I
have yet to see any evidence that a 'successful' long-range forecast is
down to anything but luck.
Humans have an inbuilt tendency to be "fooled by randomness".
http://en.wikipedia.org/wiki/Fooled_by_Randomness

Long-range forecasting reminds me of the state of short-range forecasting
when I was a lot younger. Some days you'd count yourself lucky if you got
a 6-hour forecast right but, on others, the synoptic situation allowed
you to be confident on venturing out as far as three days. Come to think
of it, 6 hours would have been a bit optimistic. I recall issuing a
forecast which went tits up in 6 minutes.

My experience tells me that long-range forecasting was possible forty
years ago given well-defined starting conditions as long as the
forecaster didn't get too ambitious. SST anomalies would give a
statistically significant prognosis as to the following month's pressure
anomaly near Iceland but accuracy would tail off the further you moved
away from that area. So forecasts for the UK tended to be a bit flaky but
were of some use. Again, that depended on the SST pattern being strong -
a weak, flabby pattern was of little use.

Returning to the current time for an example, I'd say the SST pattern
points to pressure being lower than average east of Iceland and high near
and to the west of the Azores. All well and good, but how many variations
in pressure pattern over the UK will fit that scenario? The best bet is
for a cyclonic west- or north-west flow but it's not the only solution.

Broad-scale long-range forecasting is possible - and has been so for
decades - but customers and forecasters ought not to be greedy. Expecting
an accurate forecast for the UK is like someone who complains about the
daily forecast because it told of showers for southern England but his
garden in Bracknell didn't get a drop.

--
Graham Davis, Bracknell, Berks. E-mail: change boy to man
To consider the Earth the only populated world in infinite space is as
absurd as to assert that in an entire field sown with millet only one
grain will grow. - Metrodoros, 300BC