Winter 2013/14 initial thoughts

Introduction

TheWeatherOutlook winter forecast for 2013/14 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 in recent seasons and this autumn. It is too early to say what the winter forecast will suggest this year 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.

Winter 2012/13 was quite cold with a sting in the tail, but the snow wasn't this deep!

Seasonal forecast models

A number of seasonal forecast models are available but the skill level they offer for this part of the world is low. In other words they aren't very accurate. However, I do use them as one of the inputs when making the winter forecast. Recently I've looked at the output from the International Research Institute (IRI), Coupled Forecast System (CFSv2), UK Met Office, JMA, Beijing, and Jamstec models.

The model outputs are updated at regular intervals, and tend to be expressed in terms of anomalies for temperature, pressure and precipitation. I'll not not discuss them in detail, but on balance they seem to be suggesting a slightly increased chance of high latitude northern blocking this winter. This pattern would increase the chances of a colder than average winter in the UK and western Europe. Most of these models will update again at least once before the winter begins.

Conclusion

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

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 northern blocking developing. On the other hand recent runs of medium range computer models have tended to suggest a very typical and average set-up through the second half of October.

Conclusion

Mixed, so no strong signal as the pattern.

ENSO

El Niño–Southern Oscillation (ENSO) conditions are expected to be neutral, possibly becoming slightly more positive.

Conclusion

No strong signal, but certaintly shouldn't preclude the chances of a colder than average winter.

Atlantic SSTs

Currently the SSTs are generally above average across much of the Atlantic and with a weak hurricane season this probably isn't a good set up to strongly force northern blocking. However, the May SST signal suggested the possibility of a negative North Atlantic Oscillation (NAO) 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.

Solar Activity

Solar activity has increased recently and is currently at moderate levels.

Conclusion

Less favourable to cold conditions than a couple of years ago. Note that the link between solar activity and winter weather patterns in western Europe is very controversial.

Siberian snow cover

Snow cover across parts of Siberia has built early and extensively. The link between Siberian snow cover and the west European winter is disputed but above average levels are thought by some to increase the chances of high pressure blocking and the colder backing further west.

Conclusion

Weak link, but probably favouring to a colder than average winter.

Other teleconnections (pressure patterns)

In addition to the NAO, a number of other teleconnections are often considered when making long range forecasts. These include the Pacific Decadal Oscillation (PDO), Madden-Julian Oscillation (MJO), and Quasi-biennial oscillation (QBO). The QBO has attracted quite a lot of attention recently despite being discovered in the 1950s. It is currently in a positive phase which is thought to increase the chances of westerly winds at our latitude during the winter months.

Conclusion

No strong signal for forecasting. The interaction between these teleconnections isn't well understood and even when taken in isolation there is little consistency in their state and the west European winter.

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. Stratospheric warming was widely discussed during winter 2012/13 and the views and conclusions reached were in my view very mixed.

Conclusion

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

Recent weather

Summer 2013 was often very warm and dry. The first half of autumn has been quite mixed with current signals offering a conflicting outlook, with blocking and more mobile patterns possible through the rest of October and the first half of November.

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 warm and dry conditions in the summer may lead some people to conclude a colder winter is more likely because there was a lot of high pressure blocking. I disagree with this and would be more inclined to forecast a cold winter after a wet and cool summer with everything else being equal.

So what about winter 2013/14?

Too early to make a call. At the present time things look quite balanced with very few strong signals. Despite this I'd be surprised if we have a very mild winter with only short cold snaps rather than at least one significant cold spell. We still seem to be in a period when cold winters occur relatively frequently and this is worth remembering. The coldest conditions could well come in February when the Atlantic naturally tends to become quieter and the chances of high pressure blocking over Scandinavia increases. If the cold does come then perhaps it will be mostly dry with less snow than we've seen at times in recent winters. To conclude the discussion I'd say that on balance the chances of a close to average or colder than average winter are slightly higher than the chances of a milder than average winter. However, remember that developments in the weather during the rest of autumn could well mean the TWO winter forecast will reach a significantly different conclusion.

Issued 16/10/2013  © Brian Gaze

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