Winter 2017/18 broke the spell of mild, wet and windy winter weather across the UK and now we are arguably heading into something a lot different and potentially snowier for the coming few years especially with low solar activity. The vague theory that solar activity correlates to something colder in the British Isles in winter stems from the fact that the cluster of cold winters from 2008 to 2010 fell right on the last solar minimum. Interestingly, we are now entering the next solar minimum, which is enough room to say that at least one of the next 3 winters in the British Isles should be severe, with a value for the entire winter probably of around just 2 or 3 ° C.
UK Winter temperature chart since 2007 – 2017
Forecast for winter 2018 / 19? Interestingly we are heading towards a weak El Nino for winter 2018/19. Weak or neutral El Nino’s often correlate with colder than average winter weather in the UK.
Northern Blocking: The Story of 2018.
Another factor to bear in mind is that we have had a very blocked Summer this year. Above average pressure has been around most of the time and this has allowed temperatures to really rocket. In winter northern blocking tends to lead to cold weather and snowy conditions at the surface. I’m not going to go into the science behind it but that is a key point to understand. The jet stream has remained very “wobbly” through Summer which has allowed a higher than average frequency of easterly winds to develop. When the jet stream “wobbles”, it often has very large waves and kinks in it that often allows air of an easterly or northerly origin to affect the UK.
The year the source of air has often been the near continent which gets very hot in summer and freezing in winter, allowing for the very seasonable weather we have experienced.
If the current weather pattern persists into Winter then it will be inevitable that we see some colder than average weather. Northern blocking in summer leads to hot sunny weather as it drags up hot air from the near continent but in winter cold and frosty as it drags up air from a frozen continent. With solar activity very low, I do see a higher than average occurrence of northern blocking this year, which should aid the development of cold spells.
Sea surface temperatures: the Atlantic, powerful jet stream for Autumn and Winter?
Contrary to my previous statement, it appears that some factors are loaded towards providing a strong roaring jet stream for winter 2018/19. The sharp gradient in the Atlantic between cold and warm waters, as seen below, within a short space of time is a classic signal for a strong jet stream. This means although the chance of some good blocked, cold spells are still increased this winter, we may still suffer from an occasional strong Atlantic storm. In fact this week the jet stream looks to be fairly lively with the chance of some Autumn gales.
This may result in another winter with fairly big temperature and surface conditions swings.
To summarize, long range forecasting is a very complex job and confidence at this range, given that we are still a few months from winter, is fairly low. However given that we are a) “overdue” a cold winter and b) “peaking” at solar minimum, I do think that scenes like the one below could be quite common this winter. Sales of Grit and de-icing equipment could indeed be high again. There are other factors involved that go towards making a winter forecast, we will know more about those in October time… Thank you for reading.