Science Interviews


Sat, 9th Sep 2006

Predicting The Weather

John Law from Weatherquest, UEA

Part of the show Hot Nectar, Warming Weather and Birds Missing the Spring

Helen - So we want to know: how can we predict the weather? What's this all about? How do we know that it's going to be 19 degrees in three day's time? Where do we start off with that sort of thing?

John - It's a good question. Weather prediction is a bit like putting together a big jigsaw puzzle: you get all the pieces and you just have to assemble them all in the right way. A lot of modern meteorology is derived from computer-based models which take into account all sorts of equations and parameters and put them together to make an output. But what we use here is an awful lot of bench meteorology and looking at basic fundamental physics and working out how that affects our temperatures. So by looking at the thickness of a set level of the atmosphere, we can say that a thicker part of the atmosphere would be warmer and as we see how that tracks across the country, that will have a bearing on the temperature as well.

Helen - And how soon can we predict the weather and the temperature? Can we talk about it in half an hour's time in a particular location or and hour's time or do you have to work in longer blocks of time than that?

John - With forecasting it tends to be that the sooner and shorter-term forecasts tend to be more accurate. As you go further out into the future things tend to be a little bit more variable.

Helen - So I'm better off finding out what's happening in thirty minutes than I am the end of next week. But another thing that people in England are especially keen to know is when is it going to rain? How do we go about predicting whether it's going to rain or not?

John - A good thing to do is to look at the bigger picture. Looking close to home you can't really see much. So if you look at where the weather is going to come from, that gives a better indication of what the weather has in store. So we look at things like satellite pictures to work out how the weather is developing above the Atlantic, for example, and can see how that moves across us during the week. For example, we have a tropical storm developing out in the Atlantic at the moment, which is due to come across Bermuda later this week. That is going to produce a lot of moisture and a lot of warm air that is eventually going to come across us here in England. So that's going to have a huge influence on the weather we get.

Helen - So you're basically saying that it's going to rain next week.

John - It will start raining, but we'll see.

Helen - So essentially it's all about looking at what's upstream of us and working out which way it's coming in. Is that sort of the key really?

John - That's exactly it. It's about looking at where the weather comes from and the air masses that we have. Each of them is from a different source. For example, air that comes down from the south west tends to be very moist and very warm, whereas air that's coming in off the continent is very dry. So when continental air comes across us in the summer, it tends to be very warm. But in the winter time, it's cold air and can be generally a very chilly period especially for us over in the eastern parts of England.

Helen - Do you have an excuse for when the weather forecast isn't quite right? Or are we asking far too much of you to get it perfectly right all the time?

John - I think the best thing to do is to look at why it went wrong. There's always a reason for why things didn't quite go to plan, so if you can work out why it didn't go right first of all, you can make it better next time. There are a lot of things that could potentially go awry so it's just about keeping your eye on things and keeping up to date with the latest weather.

Helen - Finally, what's the deal with the Gulf Stream with talk about climate change and so on? Is it really true that temperatures could go down now instead of up in this warming world of ours?

John - It's true that that Gulf Stream is a very important factor in our weather here. For our latitude we're about nine degrees warmer on average in this north western corner of Europe. It feeds a lot of warm water up from the Atlantic and if that were to change it would definitely have an effect on our weather here. However, it would probably be evened up with other things going on with climate change, so at the moment it's very difficult to see how much of an effect it would have.


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