A new study published today (Friday 14 September) in Environmental Research Letters, compares the latest seasonal forecast system to the one previously used . The conclusion is that the latest models can better warn the UK of extreme winter weather conditions.
The winter of 2009–2010 was known as “The Big Freeze” here in the UK and was part of the severe winter weather in Europe. It was the coldest winter since 1978-79, with a mean temperature of 1.5 °C.
Picture of the UK taken on the 7th January 2010.
The new model takes into account sudden stratospheric warmings (SSWs), which are known to be responsible for cold surface conditions. SSWs happen when the polar vortex of westerly (eastward) winds in the winter hemisphere suddenly slows down or even reverses direction, accompanied by a rise of stratospheric temperature by several tens of kelvins.
 D R Fereday, A Maidens, A Arribas, A A Scaife and J R Knight. Seasonal forecasts of northern hemisphere winter 2009/10. (2012) Environ. Res. Lett. 7 034031