Tuesday 18 October 2011

Cold Winters: Opening comments.

On 20/9/11 a UK paper, The Daily Express, published a story stating that a long term weather forecaster predicted another unusually cold winter for the UK. This is part of a general mood in Britain with many people seeming to expect colder winters on the basis of the last two winters.

In this post I'll concentrate on comparison with the 2009/10, which was an exceptional event. Whereas the following year 2010/11 was notable for the early snowfall, the winter as a whole was not really exceptional. The Arctic Oscillation (AO), having been negative in December became more neutral in January and February. This was in contrast to 2009/10's record extreme negative AO.

I should point out that whilst the general thrust of the article is of prediction of a colder than usual winter this does not mean all of the forecasters quoted below are claiming a winter as severe as that of 2009/10. Using the Daily Express list of long term weather forecasters I've tried to identify the reason these forecasters are predicting an unusually cold winter, and if indeed they're talking about conditions similar to 2009/10.

Exacta Weather in their UK long range forecast state:
Low solar activity and ocean behaviour alter atmospheric circulation and block jet stream patterns that create enhanced moisture in terms of snowfall... ...Coupled with other in depth factors such as recent volcanic activity and changes to the Gulf Stream/North Atlantic drift that we consider, this does not bode well for the severity of the UK and Northern European winter of 2011-12.

NetWeather.tv predict a likelihood of European blocking patterns, these are the patterns that are necessary for exceptionally cold UK weather. At present they are advising that January is likely to see a breakdown of the blocking highs with a predominance of low pressure in that month. This would be more similar to 2010/11's winter. NetWeather.tv's forecaster Stewart Rampling uses the Climate Forecast system from NCEP. So can be considered more 'conventional' than Exacta Weather's use of UV insolation and ocean conditions.

Currently the UK Met Office don't produce seasonal forecasts, the longest they go to is one month. Their long-term outlook is for unsettled weather (i.e. low pressure systems) into the first week of November. This tells us nothing about the winter as such.

Weather Services International, in what is essentially a teaser for a product aimed at the energy industry, back up what they stated in the Express article: A cool but stormy outlook. More here. But they don't detail what their system is, however I infer from this page that they use pretty standard techniques including numerical modelling.

Positive Weather Solutions, as of September, had not produced a long-term forecast. By 12 October they stated November would be "a little drier" and temperatures may be "slightly below average" in the North and East of the UK. This varies from the Express quote of “exceptionally dry” for two months.

So now, about a month later, based on the predictions of these forecasters, there's little concrete reason to anticipate a winter as cold as 2009/10, a year that was notable for having the lowest Arctic Oscillation index since 1950. Nonetheless there seems to be a public mood anticipating another cold snowy winter.

Later on 10/10/11 the Express published an article claiming a confused connection between cold winters and the La Nina with mention of low solar UV radiation. No mention of the other possible factors; low Arctic sea-ice and anomalous Siberian snowfall. Factors I'll be posting on shortly.
So are we in for another cold winter like the exceptional one of 2009/10 or the rather less unusual 2010/11?

I don't know.

But I'm watching Siberia's snowfall as 2009/10's exceptional low AO may have been triggered by anomalously extensive snowfall in Siberia during the last two weeks of October.


Lazarus said...

I think the mention of low solar UV radiation is due to the new research conducted by the Met Office and Imperial College London and published in the journal Nature Geoscience, showing how solar variability can help explain cold winters;


I have already see it being used by 'skeptics' by suggesting this is something that hasn't been considered before and shows how poorly the whole issue of AGW must be.

It looks like it is worth a read by the link only gives access to the abstract.

Chris Reynolds said...

Thanks Lazarus,

I wasn't aware of that paper. It's hard to see how the denialists can take comfort from it as it's yet another paper showing how models can reproduce observed phenomena.

In my next post, about the UV climate link, I discuss papers published on this link over the last 10 years. Those papers reference others going back over the last 20 years. To claim this is something new is ill-considered rubbish.