Winter 2012/13 initial thoughts - Update 28/10

Introduction
TheWeatherOutlook winter forecast for 2012/13 will be issued in late November and made freely available on the site. It is based on a number of factors such as weather patterns during recent seasons and those which develop through the 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 they seem to be more promising than last year if you're hoping for a cold winter this year. One thing I have noticed is that the latest updates from a couple of them while still suggesting the risk of a cold winter, have started reducing the probability of this outcome. The updates in the next 6 weeks will be interesting.

Conclusion
No strong signal, but leaning towards a colder and possibly drier than average winter across all parts of the country.

Pattern matching
We’re now over half way through the autumn, so although conclusions shouldn't be drawn it is interesting to see how things are developing. At this point there continue to be suggestions of northern blocking, with signs of disruption to the vortex over Greenland continuing. It also looks quite likely that a lot of the cold arctic air be funnelled down into north eastern Scandinavia and western parts of northern Russia.

Conclusion
At this stage it looks much more favourable than at the same point last year, with the possibility of a disrupted Atlantic flow at least early in the winter, allowing colder weather from the north or east (Scandinavia) across the UK.

ENSO
The winter is expected close to neutral ENSO conditions.

Conclusion
No strong signal, but a neutral ENSO could mean that if a cold block becomes established across western Europe early in the winter it will be more difficult to shift as we go through January and February. 

Atlantic SSTs
Currently SSTs remain favourable for northern blocking to develop, although the signal has weakened somewhat in the last few weeks. The May SST signal was indicating that a positive North Atlantic Oscillation (NAO) was the most likely outcome this winter. A link between the May SST profile and the NAO of the following winter has been established, so this should not be ignored.

Conclusion
No strong signal because the current -NAO profile is offset by the May +NAO signal.

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

Conclusion
The link with the weather we can expect is a controverisal one, but there is a view that lower solar activity leads to more blocked (and potentially colder) winter weather patterns across western Europe. Solar activity is weaker than this time last year, but higher than before the previous cold winters. On balance the current level of solar activity is considered more likely to increase the chance of blocking.  

 

Other teleconnections (pressure patterns)
In addition to the NAO, a number of other teleconnections are often considered when making long range forecasts, often relating to pressure patterns in the Pacific region and how these could be changed by ENSO and the Madden-Julien Oscillation (MJO).

Conclusion
No strong signal for forecasting.

 

Stratospheric temperature forecasts
In simple terms stratospheric warming is believed to encourage northern blocking. The problem is forecasting stratospheric temperatures, and fully understanding the time lag and how to use this as a forecasting tool for a small part of the Earth such as the UK.

Conclusion

Whilst I'm interested, I don't currently think it's possible to draw conclusions in this area, so to me there is no strong signal.


Recent weather
Summer 2012 was quite cool and often wet, but winter 2011 - 12 was mostly mild unlike the three previous winters. Weather patterns through the first half of autumn have been different to last year, and already cold arctic air has brought snow even to parts of southern England.

Cold winters do tend to come in clusters, but even during these periods mild winter do occur. We may well still be in a period when the chances of a particular winter being cold are higher than average.

Conclusion
The wet and coolish summer, the first half of autumn, and the weather patterns of recent years look favourable for a cold winter this year.

So what about winter 2012/13?
It's still early to make a call and I'll not do that at this point. However, in the last few weeks I would say the balance has tipped further towards colder than average conditions during the December, January and February. I'd also say the possibility of a very cold winter has increased but it will be important to see how the weather develops through November. TheWeatherOutlook winter forecast will be issued in late November. On the basis of this discussion, don’t conclude what it will be predicting because how the weather evolves during the next month is a very important consideration for me.

Issued 28/10/2012  © Brian Gaze