DW: So, you’ve spent most of your life trying to make sense of clouds. Do clouds always make sense?
SP: I think so. Look at a sky without clouds. It's boring. So if you look at the clouds, you see the weather. You can see the weather through clouds. The clouds are very important. They have different formations. And they bring the most important thing for us - for nature - life: they bring rain. So for me they are very important. But on the other hand, they are low-scale phenomena. And that means they are developing, resolving, moving, and this is very difficult for the weather forecast, for my daily job.
I'm just curious: when you walk out the door in the morning, as an expert, as a cloud expert, can you look up in the sky - and say it's covered - do you know if it's going to rain? Do you know - oh, I've got to turn around and get my umbrella?
Absolutely. I see when it's completely cloudy, when it starts raining I get my umbrella. That's not a problem. But it's not enough information for doing a good forecast. The one point is when I go out I have to make the forecast for all of Germany. When I go out in Munich and look at the sky I don't know what the sky looks like in Berlin. So that won't help. And if I don't know anything about the pressure of the air then for me it's a very big problem. So I need more information. It's a little bit like a judge who doesn't have a law. Then he can't decide anything. Sometimes I see things which help me. If the lower troposphere and the upper troposphere have different currents, different directions of the wind....
So if the clouds are moving in different directions....
then I can see OK maybe it's starting raining soon. Or if the high clouds, the cirrus clouds are increasing from one direction, I see a warm front is coming on and it'll rain. Or if a cumulonimbus is coming up, then I see maybe it's going to be... maybe I will see a thunderstorm.
Do you have a favorite type of cloud?
Absolutely, this cumulonimbus - in German it's called cumulonimbus capillatus incus - it's the big cloud with an anvil...
It looks like an anvil....
Like an anvil, because the end for a cloud is always the troposphere, at 12-13 kilometers above ground. So the cloud can't move higher. So this is a stop and that makes it like an anvil [shape]. And this cloud has a big strength so for me it's interesting to look at the heavy rain, the hail possibly, the electricity - and this for me is very important - also for the warning management, for the people I make the weather forecasts for. It's an important and a very nice cloud if you only look at the cloud as a cloud.
Weather forecasting is very vague. You often hear, you know, 'mostly sunny with a few clouds' or 'mostly cloudy with a little bit of sun.' Why is it still so vague?
Clouds are very small-scale processes. And this means developing, resolving, and always change. And this makes it very difficult for us. I can't say 'Look, tomorrow at 13:15 exactly this cloud is coming here and bringing the rainshower.' We have to summarize it. Also because I have only two minutes time for the whole of Germany. And the mathematical problem is also very interesting. The clouds are small but the equation to describe this physical process is huge. It's very difficult to solve it, so these clouds - in German I would like to translate it as: the cloud is falling through the meshes of the model grid, and that is a little bit the problem, also for us in the daily forecasts.
Well thanks for telling us about the daily forecast - the life of a German weatherman, Sven Plöger. You're on Tomorrow Today.
(Interview: Derrick Williams)