pbweather

15 days later and the original statement stands. It wasnt too early to make the statement as there was already strong support for it out to at least 10 days i.e. 26th. Therefore not enough time to change the outcome.

So I think we can chalk December off as a CET that will end up at least normal and probably around +5 or more. The AO will out turn on average above normal as will the NAO. Therefore I suggest the OPI has not worked for December. 1-0 to the Met Office long range this time around. An embarrassment for the likes of Piers Corbyn at WeatherAction and James Madden at Exacta snomageddon forecasts. However, the OPI from what I can tell only suggests at least 2/3 super negative AO months in a winter given the near record -ve value this year. So there is still time for it to claim some success.

Agree totally about your negative AO and NAO comments. A -ve AO and NAO forecast should be used as a warning of potential for cold, but it can not be used as accurate forecasting tool which is also why I seriously question how the correlation stats of the OPI are generated.

Apologies for the year confusion but some archives work on the year of the first month of winter e.g EarthSat. Using my running 10 year Dec CET 4.3 and 30 year Dec CET 4.8, then even if you use the previous years only 1976 and 2009 are below normal and the average of all years is close to normal. 2, 5.2, 6.2, 3.1, 4.8. Factor in sunspots and 1976 and 2009 were bang in the middle of very low sunspot periods which is almost certainly a factor as well so then these Dec CETs are probably not cold at all. Once you get a normal or warmer than normal Dec then getting a strongly cold winter becomes increasingly difficult because you need at least one month to cancel out Dec anomalies and this is why there is not a very clear stats relationship between -ve AO and -ve NAO winters. Similar story with all the other teleconnections as well.

Do the results speak for themselves? Blocking and -ve AO signals do not necessarily translate to cold everywhere. Look at the CET in these OPI analog years. Dec 1977 = 6.3, Dec 1985= 6.1, Dec 1987 = 5.6, Dec 2013 = 6.3 so all of these are very warm Decembers with only Dec 2010 seeing extreme cold. I would argue that Dec 2010 was in a period of exceptionally low sunspots and other drivers all lined up to bring the perfect storm of cold. So although the graphic shows anomalous pressure heights over the polar region and a southerly displaced storm track over the N Atlantic I would argue that statistically from those years the risk is warm not cold for December in the UK and probably W parts of Europe. The rest of winter is another matter, but just wanted point out that all the hype about -ve AO winters is not all it seems.