Winter 2011/12 initial thoughts

Introduction
TheWeatherOutlook winter forecast will be issued in late November, and will be based on a range of factors including the weather patterns which develop during the second half of autumn. At this juncture it is too early to confidently say what the winter forecast will suggest, but a few early thoughts are possible. Before reading on remember the caveats. Firstly, long range weather predictions for this part of the world tend to be inaccurate, and secondly, this is not the TWO winter forecast.

Seasonal forecast models
A number of seasonal forecast models are available, but my view is they often aren’t accurate, and I view them as just another input into the forecast. I’ve looked at the output from the International Research Institute (IRI), Coupled Forecast System (CFS), ECM seasonal model, UK Met Office, Meteo France, JMA and IOD.

The model outputs are updated at regular intervals, and tend to be expressed in terms of anomalies for temperature, pressure and precipitation. I won’t discuss them in detail here, but in general terms it is probably reasonable to say they are pointing towards a positive pressure anomaly across the UK, so in other words, higher pressure than the average over the winter period.

Conclusion
A drier than average winter, with temperatures close to average, possibly slightly colder further south and east.

Pattern matching
As we’re only half way through the autumn it is too early to draw conclusions here. However, there have been suggestions of less lower pressure over Greenland, with the vortex possibly setting up there.

Conclusion
Less chance of the cold patterns we’ve seen during the last couple of winters developing. Possibly if sustained cold is to develop it will be from pressure building over Scandinavia during the second half of the winter.

ENSO
The winter is expected to bring weak to moderate La Nina conditions. The link between these and the winter in Western Europe is tenuous, but there is a feeling that a strong La Nina is more likely to bring a cold start to the winter, but a mild end. On the other hand a cold winter may be more likely when a weak La Nina is present.

Conclusion
No strong signal.

Atlantic SSTs
Currently there is a cold anomaly stretching from Ireland across to New Foundland. Further north there is a warm anomaly around much of Greenland.

Conclusion
Neutral.

Solar Activity
Solar activity has increased recently, although it is still relatively low for this stage of the cycle.

Conclusion
Less favourable to cold conditions this winter than we’ve seen during periods of very low or declining solar activity such as last year.

Recent weather
Apart from the summer months, temperatures have often been above the seasonal average in the UK this year. The last three winters have all been colder than the seasonal average. Cold winters do tend to come in clusters, but even during these periods mild winter do occur.

Conclusion
The above average temperatures during most months this year, and in the first half of the autumn, outweigh the recent run of cold winters for me. So this is a weak but significant pointer to a milder winter this year.

So what about winter 2011/12?
At the moment things look finely balanced, and although I would be surprised if the winter turns out to be very mild and snowless, the chances of average or milder than average temperatures are higher than they have been for the last few years. I wouldn’t be surprised if this winter was the mildest since 2007/08, but despite this, it’s too early to discount the possibility of another cold one. If sustained cold is to come this year I suspect we’ll see a different pattern to recent winters, with more blocking over Scandinavia later in January and February. TheWeatherOutlook winter forecast will be issued in late November. On the basis of this discussion, don’t conclude it will be predicting a mild winter because how the weather evolves during the next six weeks is a very important consideration for me.

Issued 16/10/2011 © Brian Gaze