Nick Grahame, Chief Forecaster at the Met Office, talks us through the forecasting challenges this weekend.
Sometimes the atmosphere can provide a real challenge for forecasters even in the shorter range. Take for example this weekend – there’s a low pressure system over the west Atlantic and, on the face of it, appears to be heading our way. However, as it approaches our shores on Saturday night, forecast models are suggesting a large degree of uncertainty in terms of where it goes next. Some continue to bring it towards the southwest on Sunday, which would result in a rather miserable day for many southern areas. The other scenario though is for the low pressure system to stall and stay well away from us. If that happened then southern areas would stay fine and bright. In these situations, it is really important for forecasters and broadcasters to find a meaningful way to talk about the most likely outcome but then to also express the uncertainty. This is important for those who are planning events etc (it is Fathers Day on Sunday of course).
So why is there so much uncertainty?
Over the weekend, we are going to see some very complex patterns developing over the Atlantic which will ultimately determine where the low will track. For those who like technical speak, it’s called a trough disruption and forecasting this phenomenon continues to be a major challenge to both computer models and humans alike. So the best thing to do is keep up to date with the forecast to get the latest on how things are expected to develop over this weekend.
Official blog of the Met Office news team 
So a mere 3 days of forecasting is beyond the scope of all your technology. However you can say with a massive amount of hubris, and with this same technology, that there is global warming. It beggars belief.
In other words, despite your access to many tens of millions of pounds’ worth of supercomputers, you can’t guarantee greater accuracy than my old granny’s piece of seaweed.
I find it curious that your computer models can’t predict the weather this weekend, but your colleague professor Stephen Belcher, Head of the Met Office Hadley Centre, using similar or identical models running on these very same computers, is entirely convinced that “We now have rock-solid evidence to demonstrate that the world is warming”.
So basically, you expect us to believe that although you are unable to model a forced, coupled, non-linear chaotic system possessing extreme sensitivity to initial conditions sufficiently well to tell us what it is going to do in 24 hours, you are totally confident you can predict the behaviour of that system in 50 – or even 100 – years’ time.
You will have to pardon my scepticism!