Everyone's a winner

This comment just appeared on the Met Office thread, courtesy of Thinking Scientist. It's too good not to have a post of its own:

I looked at the documents Katabasis got from the FOI of the MET office. The predictions from the Met are even poorer quality than appears at first glance because their categories for mild average and cold overlap!

Mild -0.1 to +1.3 Probability 30%
Average -0.5 to +0.6 Probability 30%
Cold -1.5 to +0.4 Probability 40%

That also means their probabilities make no sense, and gives them a double dip, or even a triple dip! If the actual anomaly was, say, 0.0 then it would be in all three categories. Brilliant! Everyone's a winner...

Can anyone think of a rational explanation?

Comments

[Gareth]

mark said:

they state the table does NOT convert NE forecast to UK forecast. why is everyone applying these percentages to that table?

Thanks for the input. If I've understood what you're saying, the prediction was (plainly) for Northern Europe not the UK and the data in the table relating to the UK is sort of a summary of the historical conditions that the UK experiences with a mild, average or cold Northern Europe winter.

I'm struggling to see what use that has as a prediction.

[Viv Evans]

James P wrote on Jan 31, 2011 at 9:40 PM:
"Harrabin was trying to explain this on the R4 news this evening. He even repeated the MO wonderful statement about the (low) probability of a "cold and wintry start to the season", which is another way of suggesting that winter might be wintry. My cat knows that."

It's worse than that!
At the time of their 'forecast' the 'cold and wintry start to the season' was already in full swing (or should I say 'snow') in Scotland ...

[mark]

gareth: thats exactly as i see it. and i dont see a useful prediction iether. they also omit some of the historical data on a whim i think. imagine what that does to extrapolating a UK forecast from an NE prediction thats already 0.3,0.3,0.4 (almost flat).

[Mac]

Now here is a pretty thing.

It would appear that this Met Office probability forecast was based on Ensemble Forecasting and as such the Met Office could never have predicted the extreme cold weather experienced this winter. It transpires this widely used method of forecasting averages out extreme weather events. This method cannot be used to predict extremes of weather. It is a widely known problem, but one that appears in this instance that has never been relayed to the government.

The long range/seasonal Met Office probabilty forecast falls if the weather turns extreme.

We have been led up the Met Office garden path over this forecast, the background to it, the context in which it was made, and the claims that the Met Office did forecast extremely cold weather.

[Ben]

If they wanted it to add to 100%, then they should have had non-stupid ranges (truly, -1.5 to 0.4 C range is "cold", that's almost a tautological prediction), removed the overlap, and added "hotter" and "colder" categories. Doing that would have given a rational prediction that adds to knowledge of humanity rather than deceptivity that can be detected by anyone glancing at the data.

Of course, as "hotter" and "colder" would have to be ~20% each (the "average" is completely overlapped, plus the -0.1 to +0.4 range of triple overlap, which would be roughly in the 10-15% area), that would not be a very convincing prediction.

[UC]

'typical limits' seem to be 1-sigma values from Figure 1 data. That would mean that UK prediction is a mixture,

if NE is Cold then UK temperature follows N(3.95,0.95)

etc.

but this is just my guess.