Anyone looking at our current 16-30 day UK forecast (for the first half of February) will have noticed that uncertainty is the theme – much more so than usual, even when looking this far ahead.
The outlook for this period is finely balanced, with two scenarios looking equally possible: the first being a continuation of the changeable and relatively mild conditions we’ve seen so far this winter; the second being a shift to a period of much colder weather.
Whilst two different outcomes are possible, it does look as though the general pattern that establishes itself by the start of February could last for quite a while, perhaps even until the middle of the month.
However, it is not possible to say which of the two scenarios is more likely due to an unusual amount of uncertainty in the forecast.
For these longer range outlooks, we use sophisticated techniques to understand the uncertainties – called ensemble forecasts.
In an ensemble forecast we run a forecast model many times from very slightly different starting conditions. The range of different outcomes gives us a measure of how confident or uncertain we should be in the overall forecast.
Currently the ensembles for the start of February onwards show a fairly even split that does not clearly favour either the mild or the cold option – and there are relatively few solutions in between.
There is a possible explanation for this relatively rare situation. In recent days there has been an increase in temperatures in the high atmosphere (the stratosphere) over the northern hemisphere. This change seems to have been driven in part by marked changes in the weather patterns lower down in the atmosphere – over the north Pacific for example.
Research, developed in part by the Met Office, suggests that changes such as this high up in our atmosphere can – in time – go on to affect weather patterns at surface-level. However, this is a new and very complex area of meteorology where we are still developing our understanding of all the mechanisms involved.
It is possible this is why we are seeing the volatility in the current forecast, as different model runs handle the interactions differently.
Rest assured, whatever happens we’ll keep you up to date with the latest information through our forecasts and weather warnings – so as soon as we know, you’ll know.
Official blog of the Met Office news team 
Interesting. It would be really good for us punters if, when you are blogging such info, you add pressure charts for your possible scenarios – I am sure you have mountains of these. So for example – the milder scenario. the high not far south presumably, and for the cold scenario…. well that’s what I’d like to see. The Siberian high is particular;ly noticeable this year for its absence in the west) and even in west Russia), so is the potential cold an arctic low sitting over or to east of us? or does high shift to Scandinavia? Can’t wait to find out. I’d put my money on the milder scenario though. We had no azores high last summer and now it’s been very evident since mid December. …..
Why is the met office still sitting on the fence.Al models are trending cold yet you still say 50/50.
Think your more worried about your credibility if you get it wrong.Well it hasn’t recovered from your winter and summer forecasts a couple years back anyway.
So you might as well hype up the cold blast anyway!
The Met Office look at a large number of models from all across the world when making assessments about the weather and for many days now there has been a very even split on the persistence of either mild or cold, with some models changing significantly from run to run. This is not unexpected when the atmosphere is so finely balanced as it is right now. We take our respsonsibility to provide the best advice possible to the public when it matters and our 6-15 and 16-30 day forecasts are updated regularly on our website by our expert forecasts. You may also want to check out the latest blog post as models increase in consensus a little more for the longer term at https://metofficenews.wordpress.com/2012/01/25/cold-weather-winning-the-war-of-probabilities/ which provides a little more context behind our most up to date forecasts.