Both radar and satellite show you weather from above, and most weather sites use them together without saying which is which. They measure completely different things, and knowing which one you are looking at explains most of the odd behaviour people notice on weather maps.
Overview
Radar looks up from the ground. Satellite looks down from space. Radar sends out a pulse of microwave energy and measures what bounces back off raindrops, hail and snow, so it detects precipitation directly. Satellite instruments measure light and infrared radiation emitted or reflected by cloud tops, so they detect clouds — and precipitation only by inference.
That single difference explains why a satellite image can show thick cloud over your city while the radar shows nothing falling, and why radar sometimes shows rain in an area that looks clear from space.
What Radar Does Well
- Detects actual precipitation. If radar shows a return, there really is water or ice in the air at that spot.
- Measures intensity. Reflectivity translates directly into how hard it is raining, which is why radar maps use a colour scale. See rain radar colours explained.
- Very high time resolution. Most national networks complete a scan every 5 to 10 minutes, so you can watch a storm actually move.
- Fine spatial detail. Individual showers and the internal structure of a thunderstorm are visible.
- Detects rotation. Doppler radar measures the speed of raindrops towards or away from the station, which is how tornado-producing mesocyclones are identified.
What Radar Cannot Do
- Reach far. Useful range is roughly 150–250 km from each station. Beyond that, coverage falls away.
- See over the horizon. The Earth curves and the beam does not. At long range the beam is scanning thousands of metres up, missing low drizzle entirely.
- Cover oceans. Radar needs a ground station. Most of the world’s ocean surface has none.
- See through mountains. High terrain blocks the beam and creates shadows behind it.
What Satellite Does Well
- Covers everywhere. Geostationary satellites see entire hemispheres, including oceans, deserts and polar regions with no radar at all.
- Shows storm structure at scale. The spiral of a hurricane, the anvil of a thunderstorm and the sweep of a frontal system are far clearer from space.
- Measures cloud-top temperature. Infrared imagery reveals how high cloud tops are, and very cold tops indicate deep, vigorous convection — a good proxy for severe weather.
- Tracks systems days out. A developing tropical system in mid-ocean is visible long before it approaches any radar.
What Satellite Cannot Do
- Confirm rain is falling. It sees the cloud, not the raindrop. Thick cloud producing nothing looks much like thick cloud producing a downpour.
- Measure intensity precisely. Satellite precipitation is an estimate derived from cloud properties, not a direct measurement.
- See beneath cloud layers. High cirrus can hide the weather-producing cloud underneath it.
- Update as fast. Typical refresh is 10 to 15 minutes, and visible imagery is unavailable at night.
How They Are Used Together
Modern precipitation maps, including the ones on RainyMap, blend the two. Where ground radar exists, radar dominates because it is the direct measurement. Where it does not — over oceans, across much of Africa and South America, and in the gaps between stations — satellite estimates fill in. The result is global coverage where the underlying quality varies by region, which is worth remembering when you are looking at a mid-ocean system.
You can see this on the real-time rain map: detail over Europe and North America is sharper than over the open Atlantic, because different instruments are doing the work.
Frequently Asked Questions
What is the difference between weather radar and satellite?
Radar transmits microwave pulses from ground stations and measures what bounces back off precipitation, so it detects rain, hail and snow directly. Satellites observe from orbit and measure radiation from cloud tops, so they detect clouds and can only estimate precipitation indirectly.
Which is more accurate for rain, radar or satellite?
Radar, wherever it is available. It measures precipitation directly rather than inferring it, and it has finer spatial and time resolution. Satellite is more accurate only where there is no radar coverage at all, such as over oceans.
Why does the satellite show clouds but the radar shows no rain?
Because cloud and rain are not the same thing. Most clouds produce no precipitation. Satellite sees the cloud deck; radar tells you whether anything is actually falling out of it.
Why is there no radar coverage over the ocean?
Weather radar requires a ground station, and its useful range is roughly 150 to 250 km. Beyond coastal stations there is nothing to transmit from, so ocean precipitation is estimated from satellite instead.
Can radar see hurricanes?
Only once they come within range of a coastal station, typically within about 200 km of land. Hurricanes are tracked across open ocean by satellite, and by reconnaissance aircraft, until they approach the coast. See our hurricane season radar guide.
Does satellite work at night?
Infrared and microwave instruments work continuously, day and night. Visible-light imagery does not, which is why night-time satellite pictures are usually infrared and look different from daytime ones.