In message , Adrian D. Shaw
writes
Felly sgrifennodd Philip Eden philipATweatherHYPHENukDOTcom:
Let me throw another thought into the discussion. A -ve winter NAOi
does not automatically guarantee a -ve winter CET. (OK, I know that's
not quite what was offered, but it's what people are expecting). A quick
flick through the individual monthly sea-level pressure charts for the
last 30 years suggests that the relationship between NAOi and CET
may also be something like 2/3 (maybe a little more, but not much).

So, if we accept that figure, the possible outcomes a
44% colder than average with a -ve NAOi
22% colder than average with a +ve NAOi
22% warmer than average with a -ve NAOi
11% warmer than average with a +ve NAOi

So, if the forecast is right for the wrong reason, is it a success?
If it is wrong, but for the right reason, is that a success?

Interesting, thanks for these figures!

The Met Office figures still add up though, using your 2/3 relationship.

They forecast a -ve NAO with 2/3 probability, therefore by inference also
a +ve NAO with 1/3 probability.

The forecast of a cooler than average winter for central Europe was
based on:

44% chance of colder than average with -ve NAO
22% chance of colder than average with +ve NAO

= 66% chance of colder than average winter.

Assuming that actually is how they arrived at their 2/3 chance (maybe an
assumption too far), then the forecast was right (for Central Europe, at
least).

But what is right, when we're talking percentages, rather than black and
white/yes and no? Really, it just provides more data to plug back into
the statistics for another year. But to put it another way, I doubt that
many Europeans would say that the forecast was misleading.
Adrian, when I was in the Office we used to work on a zonal index which
I understood to be the mean of the surface pressure difference between
the Azores and Reykavik. I would be interested to see the upper air
anomalies this winter. Whether they be 500MB, Total thickness or 300MB.
I was used to working at 300MB while CFO (as it was then) used 250MB
both for obvious reasons. (Jet stream).
Although I have no data I think I can still suggest that the
semi-sinusoidal upper pattern over the eastern northern Atlantic has
been fairly static in January. I suppose the NAO is based on the upper
air, in January the upper ridge was maintained by a series of confluent
upper troughs relaxing to the south of Iceland thereby maintaining a
semi-permanent upper ridge and the surface high over northern UK.
As you may gather from my cautious wording - I stand to be corrected.
Cheers
Paul
--
'Wisest are they that know they do not know.' Socrates.
Paul Bartlett FRMetS
www.rutnet.co.uk Go to local weather.
400FT AMSL 25Miles Southwest of the Wash