Winter 2007/08 early thoughts

Introduction
TheWeatherOutlook winter forecast will be issued in late November, and will take into account a range of factors including the weather patterns which developed during the autumn. So as we are only just over half way through the autumn it is too early for us to say what the forecast is likely to suggest, but at this juncture a few early thoughts on the winter weather are possible. Before reading on, here are a couple of caveats. Firstly, as ever remember that all long range predictions for this part of the world tend to be inaccurate and secondly, this is not intended to be a forecast.

What data is available already?
North Atlantic Oscillation (NAO) forecasts
UCL (see here)
Slightly below average, with the probabilities favouring slightly below average temperatures and close to average precipitation.

UK Met Office (see here)
Weakly negative, possibly suggesting close to average winter temperatures and precipitation levels.

Seasonal forecast models
UK Met Office (see here)
The available data from the Met Office and the European Centre for Medium-Range Weather Forecasts (ECMWF) is pointing towards a milder than average winter. The September update above average temperatures across most of Europe (including the UK) during the winter months.

International Research Institute (IRI) seasonal charts (see here)

The charts issued this October are indicating a milder than average winter across Europe.

Pattern matching
This involves looking at the weather patterns from previous autumns to see how they compare with the evolution this year. The winters which followed the closest matching autumns are then used as a template to produce a forecast for the winter ahead. Summer 2007 brought temperatures close to average temperatures to the UK, which may sound nothing special, but recent years have generally brought relatively warm summers. Therefore, summer 2007 for much of the UK was notable for being wet and cooler than we have become accustomed to. The autumn has so far followed an unusual pattern with close to average temperatures during September and very little unsettled and stormy weather which is often typical at this time of year. High pressure has built and remained close to the UK for most of the time bringing much dry weather.

Temperatures in the UK this year
After a long stretch of warmer than average months, temperatures have trended back towards the average in the UK during the last 5 months or so. The summer this year was cooler than in many recent years. Autumn also started with close to average temperatures. The temperature profile during the last year may be used to suggest colder conditions are perhaps more likely this winter than in most other recent  years.

ENSO
The winter is expected to bring La Nina conditions. The link between these and the winter in western Europe is tenuous, but there is a feeling that it can lead to increasingly unsettled weather later in the winter. If this is the case it would tend to favour milder conditions later in the winter.

Solar activity
This is very controversial, but it has been suggested that lower solar activity leads to a less active jet stream. Solar activity (measured by the number of sun spots) is currently very low. If this is believed it may be argued that current levels of solar activity are conducive to a colder winter.

So what about winter 2007/08?
My view at the moment is that there are some signals which indicate an increased chance of a colder winter this year, but overall the probabilities still currently favour an average or milder than average winter. After all cold winters have become an extremely rare commodity in the UK during the last 20 years, and even if a Siberian block does build and hold there is no guarantee that it will extend its influence as far west as the UK. For example, it’s not that unusual to see cold weather push west out of Russia and then grind to a halt over central Germany as it begins to encounter the energy of the Atlantic. If the UK is to experience a cold winter so many factors have to come together at the right time that the probability of this happening is never high. None the less, sooner or later the UK is bound to experience another cold or very cold winter with widespread snow. There are some pointers suggesting that it may happen this winter, and hopefully things will be slightly clearer by the time TheWeatherOutlook winter forecast is published. 

Issued 21/10/2007 © Brian Gaze