J C-W wrote in message
news

"Franz Heymann" wrote in message
...
The following is true (I'm a sad soul). At the beginning of the year I
did
a
small experiment noting forecasts and noting what actually happened
for
my
city over 3 weeks (I got bored after 3 weeks). I collected each
forecast
for
the following day only, no long range stuff. The three sites were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out tops
with
60 something %. I wish I'd kept the figures now. My conclusion was,
it's
best to look out of the window :-) And... my goodness are they getting
paid
for this??!

That means that Yahoo was far and away the best forecaster. If you
rigorously stuck to the opposite of what they said, you would have had
70%
accuracy.

Franz

Er... somewhat flawed logic - just because it's right for 30% of the time,
does not mean that the opposite is true for 70% since there are so many
meteorological variables (i.e. the opposite could be just as wrong). What
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because they
rely on basic physical principles and ignore chaos theory, quantum
mechanics
and the insight of a deity. The suggestion of looking out of one's window
or using the old fashioned techniques (pine cones, 'red sky at night...',
feeling in the bones) may prove just as useful and accurate!

Jason




I wished afterwards that I had predicted the weather myself also, to see how
well I would have done. I was going to do the experiment again and before
starting, I was going to put various "possible weathers" into a hat, then
pull them out and add them in advance to each day before beginning the
experiment with the three websites. I never did it though. I don't think I
would have had much chance of a high score doing it this way, but if I'd
predicted it the day before as the forecasters do *and* listened to my
bones, looked at my pine cone and the sky, then I can't see any reason for
not doing as well as the met office's 60 something %. And then, I could have
set up my own weather website could I not?!

I was quite lenient with my experiment by the way. The met office always
predicted higher temperatures than actually materialised, but I let them off
if the weather was correct. The other two seemed better on temperatures but
would predicted rain when the sun shone and visa versa. I considered this
more seriously wrong than the temperature problems and so this is possibly
why they came out with a lower score.



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Kay Easton wrote in message
...
In article , anne
writes


The following is true (I'm a sad soul). At the beginning of the year I
did a
small experiment noting forecasts and noting what actually happened for
my
city over 3 weeks (I got bored after 3 weeks). I collected each forecast
for
the following day only, no long range stuff. The three sites were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out tops
with
60 something %. I wish I'd kept the figures now. My conclusion was, it's
best to look out of the window :-) And... my goodness are they getting
paid
for this??!


Apparently the chance of being right if you forecast tomorrow's weather
as being the same as today's is 67%


Goodness! I'll begin an experiment tomorrow ;-)




--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm

On Tue, 23 Sep 2003 18:01:30 +0100, "J C-W"
wrote:


"Franz Heymann" wrote in message
...
The following is true (I'm a sad soul). At the beginning of the year I
did
a
small experiment noting forecasts and noting what actually happened for
my
city over 3 weeks (I got bored after 3 weeks). I collected each forecast
for
the following day only, no long range stuff. The three sites were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out tops
with
60 something %. I wish I'd kept the figures now. My conclusion was, it's
best to look out of the window :-) And... my goodness are they getting
paid
for this??!

That means that Yahoo was far and away the best forecaster. If you
rigorously stuck to the opposite of what they said, you would have had 70%
accuracy.

Franz

Er... somewhat flawed logic - just because it's right for 30% of the time,
does not mean that the opposite is true for 70% since there are so many
meteorological variables (i.e. the opposite could be just as wrong). What
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because they
rely on basic physical principles and ignore chaos theory, quantum mechanics
and the insight of a deity.

Sadly, I've never knowingly been "au fait" with the insight of a deity
..... especially in relation to weather forecasting. In my experience
he/she/it/they always keep(s) me guessing....!! Now.. quantum chaos I
can relate to!
(;-)
Regards
Geoff

"J C-W" wrote in message
news

"Franz Heymann" wrote in message
...
The following is true (I'm a sad soul). At the beginning of the year I
did
a
small experiment noting forecasts and noting what actually happened
for
my
city over 3 weeks (I got bored after 3 weeks). I collected each
forecast
for
the following day only, no long range stuff. The three sites were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out tops
with
60 something %. I wish I'd kept the figures now. My conclusion was,
it's
best to look out of the window :-) And... my goodness are they getting
paid
for this??!

That means that Yahoo was far and away the best forecaster. If you
rigorously stuck to the opposite of what they said, you would have had
70%
accuracy.

Franz

Er... somewhat flawed logic

Of course. Did you miss the tongue pushing against my cheek?

- just because it's right for 30% of the time,
does not mean that the opposite is true for 70% since there are so many
meteorological variables (i.e. the opposite could be just as wrong).

That is also somewhat flawed logic. If it is right for 30% of the time then
it quite certainly has to be wrong for 70% of the time, unless there are
illogical situations which are neither right nor wrong
{:-))

What
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because they
rely on basic physical principles and ignore chaos theory, quantum
mechanics
and the insight of a deity.

I doubt if quantum mechanics and a deity play major roles. The main bugbear
is the fact that the weather equations are chaotic.

The suggestion of looking out of one's window
or using the old fashioned techniques (pine cones, 'red sky at night...',
feeling in the bones) may prove just as useful and accurate!

I once had a mammoth South African calendar with one page per day. Each
page had a scene with the caption "It's a sunny day today". It was correct
for
approximately 95% of the days of the year. I never even owned a raincoat
until I went to University.

Franz

wrote in message
...
On Tue, 23 Sep 2003 18:01:30 +0100, "J C-W"
wrote:


"Franz Heymann" wrote in message
...
The following is true (I'm a sad soul). At the beginning of the year
I
did
a
small experiment noting forecasts and noting what actually happened
for
my
city over 3 weeks (I got bored after 3 weeks). I collected each
forecast
for
the following day only, no long range stuff. The three sites were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out
tops
with
60 something %. I wish I'd kept the figures now. My conclusion was,
it's
best to look out of the window :-) And... my goodness are they
getting
paid
for this??!

That means that Yahoo was far and away the best forecaster. If you
rigorously stuck to the opposite of what they said, you would have had
70%
accuracy.

Franz

Er... somewhat flawed logic - just because it's right for 30% of the
time,
does not mean that the opposite is true for 70% since there are so many
meteorological variables (i.e. the opposite could be just as wrong).
What
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because they
rely on basic physical principles and ignore chaos theory, quantum
mechanics
and the insight of a deity.

Sadly, I've never knowingly been "au fait" with the insight of a deity
.... especially in relation to weather forecasting. In my experience
he/she/it/they always keep(s) me guessing....!! Now.. quantum chaos I
can relate to!
(;-)

The chaos which makes weather prediction a jocular affair is not
particularly closely connected with quantum effects. It occurs in the
classical weather equations. In fact, it was a study of a classical weather
model which led to the discovery of chaos.

Franz

"Kay Easton" wrote in message
...
In article , Martin Sykes
writes
http://www.users.globalnet.co.uk/~sykesm
"Sad Sid" . wrote in message
...
This is one area where I never trust the beeb!
I prefer to get my weather forecast from Yahoo - their local forecasts
are
invariably right.
For example, when I planned to go to Royal Welsh Show (60 miles away)
Yahoo
forecast light rain for my home town, sunny bright in Builth. That's
exactly
what happened. (The Beeb said "rain over South Wales", which would have
stopped me going)
Try http://weather.yahoo.com/forecast/UKXX1404.html



This site is usually pretty good too and it gives a full 10-day forecast:
http://uk.weather.com/weather/local

It looks like the same selection of locations as the yahoo site, so I
guess they get their data from the same source.

This site is more honest about the accuracy though - eg the Otley data
is 'as reported for Leeds' (a couple of hundred feet lower and in the
next valley) and the Settle (Yorkshire Dales) figures are simple the
Manchester ones.

So although at first sight it looks wonderfully useful for local info,
it is an illusion ;-)

Quite so. The surface of the world is divided into a large number of cells
for doing the calculations for the weather predictions, and these cells are
very much larger than any which those weather URL's pretend to be the case.

Franz

"Franz Heymann" wrote in message
...

wrote in message
...
On Tue, 23 Sep 2003 18:01:30 +0100, "J C-W"
wrote:


"Franz Heymann" wrote in message
...
The following is true (I'm a sad soul). At the beginning of the
year
I
did
a
small experiment noting forecasts and noting what actually happened
for
my
city over 3 weeks (I got bored after 3 weeks). I collected each
forecast
for
the following day only, no long range stuff. The three sites were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out
tops
with
60 something %. I wish I'd kept the figures now. My conclusion was,
it's
best to look out of the window :-) And... my goodness are they
getting
paid
for this??!

That means that Yahoo was far and away the best forecaster. If you
rigorously stuck to the opposite of what they said, you would have
had
70%
accuracy.

Franz

Er... somewhat flawed logic - just because it's right for 30% of the
time,
does not mean that the opposite is true for 70% since there are so many
meteorological variables (i.e. the opposite could be just as wrong).
What
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because
they
rely on basic physical principles and ignore chaos theory, quantum
mechanics
and the insight of a deity.

Sadly, I've never knowingly been "au fait" with the insight of a deity
.... especially in relation to weather forecasting. In my experience
he/she/it/they always keep(s) me guessing....!! Now.. quantum chaos I
can relate to!
(;-)

The chaos which makes weather prediction a jocular affair is not
particularly closely connected with quantum effects. It occurs in the
classical weather equations. In fact, it was a study of a classical
weather
model which led to the discovery of chaos.

Franz


You obviously don't subscribe to Prof Sir Roger Penrose's viewpoint on the
undiscovered links between quantum mechanics and macro-scale classical
physics, particularly where those laws break down or fail to be able to
predict observable phenomenon! There are quite a lot of theorists out there
researching this very thing - a quick search on Google brings a lot of them
to the fore (e.g. http://amselvam.tripod.com/ ). But, alas, we are straying
from gardening into another, somewhat off-topic conversation [give myself a
slapped wrist]....

J


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.520 / Virus Database: 318 - Release Date: 18/09/2003

http://www.users.globalnet.co.uk/~sykesm
"J C-W" wrote in message
news
big snip
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because they
rely on basic physical principles and ignore chaos theory, quantum
mechanics

As I understand modern weather prediction, they acknowledge the existence of
chaos. Chaos does not violate the laws of physics but simply acknowledges
that even simple laws can give rise to complex behaviour which can be
massively influenced by minute variations in the initial state.

To get over this they run millions of simulations with small variations in
the input state. For some states, all simulations run very closely but for
others they diverge quickly. They then use all the simulations to give
statistics like '70% probability of rain' which really means that in 70% of
the simulations it rained and in the other 30% the simulation took a
different course and it remained dry.
--
Martin & Anna Sykes

"J C-W" wrote in message
...

"Franz Heymann" wrote in message
...

wrote in message
...
On Tue, 23 Sep 2003 18:01:30 +0100, "J C-W"
wrote:


"Franz Heymann" wrote in message
...
The following is true (I'm a sad soul). At the beginning of the
year
I
did
a
small experiment noting forecasts and noting what actually
happened
for
my
city over 3 weeks (I got bored after 3 weeks). I collected each
forecast
for
the following day only, no long range stuff. The three sites
were
Yahooo,
UK Weather.com and the Met Office. Yahoo had something like a 30%
accuracy,
UK Weather.com were about 40% I think and the Met Office came out
tops
with
60 something %. I wish I'd kept the figures now. My conclusion
was,
it's
best to look out of the window :-) And... my goodness are they
getting
paid
for this??!

That means that Yahoo was far and away the best forecaster. If you
rigorously stuck to the opposite of what they said, you would have
had
70%
accuracy.

Franz

Er... somewhat flawed logic - just because it's right for 30% of the
time,
does not mean that the opposite is true for 70% since there are so
many
meteorological variables (i.e. the opposite could be just as wrong).
What
this thread tells us is that for all the technology and super
computer
models being used, the predictions are fundamentally flawed because
they
rely on basic physical principles and ignore chaos theory, quantum
mechanics
and the insight of a deity.

Sadly, I've never knowingly been "au fait" with the insight of a deity
.... especially in relation to weather forecasting. In my experience
he/she/it/they always keep(s) me guessing....!! Now.. quantum chaos I
can relate to!
(;-)

The chaos which makes weather prediction a jocular affair is not
particularly closely connected with quantum effects. It occurs in the
classical weather equations. In fact, it was a study of a classical
weather
model which led to the discovery of chaos.

Franz


You obviously don't subscribe to Prof Sir Roger Penrose's viewpoint on the
undiscovered links between quantum mechanics and macro-scale classical
physics, particularly where those laws break down or fail to be able to
predict observable phenomenon!

Those viewpoints of Penrose do not affect the nature of chaos. Chaos is
associated with most (probably all?) those equations of dynamical systems
which are highly non-linear. Quantum mechanics does not have to be
involved. Newton's equations for planetary systems, which predated quantum
mechanics by a few centuries, can have chaotic solutions.

But we are a long, long way from gardening.......................

There are quite a lot of theorists out there
researching this very thing - a quick search on Google brings a lot of
them
to the fore (e.g. http://amselvam.tripod.com/ ). But, alas, we are
straying
from gardening into another, somewhat off-topic conversation [give myself
a
slapped wrist]....

Two of my colleagues and I were probably the first folk to have investigated
a classical chaotic system before the concept was invented. We were,
however too stupid to recognise what was going on, and ascribed the peculiar
behaviour of our calculations to the results of rounding-off errors in our
mechanical calculator. ( The work predates the availability of solid state
computers by a decade or so)

Urglers, please forgive us for wandering so far from the garden......

Franz

"Martin Sykes" wrote in message
...


http://www.users.globalnet.co.uk/~sykesm
"J C-W" wrote in message
news
big snip
this thread tells us is that for all the technology and super computer
models being used, the predictions are fundamentally flawed because they
rely on basic physical principles and ignore chaos theory, quantum
mechanics

As I understand modern weather prediction, they acknowledge the existence
of
chaos. Chaos does not violate the laws of physics but simply acknowledges
that even simple laws can give rise to complex behaviour which can be
massively influenced by minute variations in the initial state.

To get over this they run millions of simulations with small variations in
the input state. For some states, all simulations run very closely but for
others they diverge quickly. They then use all the simulations to give
statistics like '70% probability of rain' which really means that in 70%
of
the simulations it rained and in the other 30% the simulation took a
different course and it remained dry.

I doubt if they run millions of simulations for one situation. If they did,
it might take them a year to produce tomorrow's forecast Two or three
closely similar cases probably would be enough for them to form a judgement
as to whether they are in a chaotic regime or not.

Franz

In article ,
(Franz Heymann) wrote:

I doubt if they run millions of simulations for one situation. If
they did, it might take them a year to produce tomorrow's forecast

They have quite powerful computers these days and lots of them.

Steve Harris - Cheltenham - Real address steve AT netservs DOT com

In article ,
(Steve Harris) writes:
| In article ,
| (Franz Heymann) wrote:
|
| I doubt if they run millions of simulations for one situation. If
| they did, it might take them a year to produce tomorrow's forecast
|
| They have quite powerful computers these days and lots of them.

They still don't run millions of simulations for one situation.
And the effect of numerical instability isn't just in terms of
small variations in the input, but is in the calculations
themselves. Despite the pop mathematics publications, the causes
and problems of computational chaos (in this sense) have been well
understood for over a century.

That being said, your posting was considerably more on the ball
than "J C-W"'s. I wish him the joy of Penrose's writings - but
going into the latter's eccentricities is definitely off-group.
Let it suffice to say that his quantum theories have found almost
no followers among scientists and mathematicians, however popular
they are with the lay press.


Regards,
Nick Maclaren.

"Steve Harris" wrote in message
...
In article ,
(Franz Heymann) wrote:

I doubt if they run millions of simulations for one situation. If
they did, it might take them a year to produce tomorrow's forecast

They have quite powerful computers these days and lots of them.

Steve Harris - Cheltenham - Real address steve AT netservs DOT com

I checked it out. The following MET Office page says they run 51 in total
( the base case and 50 similar versions ). It also explains a bit about how
they combine the results.

Incidentally, I haven't done anything in the garden except mow the lawn for
the last 2 months due to back problems. In some parts now, chaos is very
much relevent.


http://www.meto.gov.uk/research/nwp/...9/predict.html

--
Martin & Anna Sykes
http://www.users.globalnet.co.uk/~sykesm

The most accurate weather forcast I heard (on BBC TV) was
"It may rain at times in places."
Beat that for accuracy if you can.
Cheers
John T

"Steve Harris" wrote in message
...
In article ,
(Franz Heymann) wrote:

I doubt if they run millions of simulations for one situation. If
they did, it might take them a year to produce tomorrow's forecast

They have quite powerful computers these days and lots of them.

Yes. My understanding is that they use them to handle data on a smaller
sized net rather than to do millions of simulations for the same situation.

Franz

Steve Harris - Cheltenham - Real address steve AT netservs DOT com