Two images, two directions of view — and both are right
On the map you can switch between radar and satellite. Both show weather, but they measure something quite different: radar measures precipitation from the ground, the satellite photographs clouds from space. That is why there can be clouds without rain — and rain without a striking cloud on the satellite image.
The short answer
If you only take away one sentenceWant to know whether it is about to rain right now?
Use the radar. It shows precipitation directly and refreshes every five minutes.
Want to see the big picture?
Use the satellite. It shows cloud fields, fronts and low-pressure systems in context.
From belowWhat the radar does
A weather radar stands on the ground and sends short radio pulses up at an angle. When such a pulse hits raindrops, snowflakes or hailstones, part of it is scattered back. The travel time gives the distance, the strength of the echo gives the intensity of the precipitation.
So the radar does not measure clouds — it measures what falls out of them. A thick but dry cloud deck is invisible to the radar: the area stays empty on the image even though the sky is grey.
From aboveWhat the satellite does
A weather satellite sits about 36,000 kilometres above the equator and keeps looking at the same disc of the Earth. It measures the light and the heat radiation arriving from below — and that produces the images that look like a view from space.
The satellite therefore mainly sees cloud tops. What happens underneath stays hidden: it can only estimate whether rain is falling out of a cloud, for example from how cold and how high the cloud top is. In return it sees the whole disc at once, including oceans and deserts where there is not a single radar.
Side by side
Same question, two answers| Radar | Satellite | |
|---|---|---|
| Measures | Precipitation — rain, snow, hail | Clouds and heat radiation |
| Direction of view | from the ground, upwards at an angle | from space, straight down |
| Refreshes | every 5 minutes | every 10 minutes |
| Coverage | only where radar towers stand — for us, Europe and the USA | area-wide — for us, Europe and the USA |
| Strength | shows exactly where and how hard it is raining | shows fronts, lows and cloud fields in context |
| Weakness | cannot see dry clouds; mountains cast shadows | cannot say for certain whether rain reaches the ground |
| Forecast | yes, up to +60 minutes from the motion of the echoes | no — the satellite shows the present state |
| At night | just as good | yes, via the heat radiation |
When they disagreeWhy the two images differ
It happens regularly that the satellite shows a thick cloud while the radar reports nothing in the same place. That is not a fault, it is the normal case: not every cloud drops anything. The other way round, light drizzle can fall from shallow clouds that barely stand out on the satellite image.
And there is a third case: rain that evaporates on the way down. The radar sees it up in the air, but nothing arrives at the ground.
What neither of them can do
Honest is honestRadar: gaps in coverage
Radar only reaches a few hundred kilometres, and mountains cast shadows. There is no radar image over the open Atlantic.
Radar: not everywhere in the world
We receive radar data from Europe and the USA.
Satellite: a shallow viewing angle
The further from the equator, the more oblique the satellite view — clouds then appear displaced and distorted.
Satellite: no look beneath the deck
Under a high cloud deck the satellite cannot see what is going on. A thunderstorm below cirrus only shows up on the radar.
Where our images come from
Sources in plain wordsRadar Europe
A network of national weather services — among them DWD, AEMET, Météo-France and the Met Office. We assemble the individual images into one European picture.
Radar USA
NOAA MRMS, the nationwide US radar network.
Satellite Europe
EUMETSAT, the European weather satellites. The derived products — cloud type, rain rate and cloud-top height — come from there too.
Satellite Americas
NOAA GOES, the American weather satellites.
Both on one map
On the weather map you switch between radar and satellite with one click — and put lightning or clouds on top.