Does red on a radar mean a tornado?

No. Red indicates a strong reflectivity return, usually heavy rain or a thunderstorm core. Tornado detection relies on velocity data and on warnings issued by the National Weather Service.

Why does radar show rain when it is not raining here?

The radar beam rises with distance as the earth curves away. Far from the radar it may be sampling precipitation high in the atmosphere that evaporates before it reaches the ground.

Can radar tell rain from hail?

Not reliably from reflectivity alone. Hail is large and dense and returns energy very strongly, so it can appear as the same intense colour as the heaviest rain.

What the colors on a weather radar mean

Radar colour is not rainfall. It is a measure of how much energy the radar beam got back, and understanding that difference explains most of the times a radar looks alarming and the weather outside does not match.

What the radar is actually measuring

A weather radar sends out a pulse of energy and listens for what returns. Raindrops, snowflakes, hail and even insects reflect some of it back. The strength of that return is called reflectivity, and the colour scale is a picture of reflectivity, not of how much water is reaching the ground.

Bigger and denser objects reflect far more strongly than small ones. That single fact explains most of the confusion below.

Reading the scale

The National Weather Service uses a consistent progression. Blues and light greens are the weakest returns, often light rain or drizzle. Greens are steady rain. Yellows mark a step up into moderate and heavy rain. Reds are heavy rain and usually a thunderstorm core. Magenta and violet are the strongest returns on the scale.

The exact value each colour represents is published by the Weather Service with the imagery itself, which is why this site draws its radar key from the government's own legend for the layer being displayed rather than approximating it.

The thing radar colour cannot tell you

Radar cannot reliably separate very heavy rain from hail. Hailstones are large and dense, so they return energy extremely strongly, and a hail core often paints the same red or magenta as the most torrential rain. A dramatic red blob may be a downpour, or it may be hail, and the reflectivity image alone will not settle it.

Radar also cannot see everything. The beam travels in a straight line while the earth curves away beneath it, so the farther from the radar site, the higher above the ground it is looking. Far from a radar, light precipitation near the surface can be missed entirely.

Common questions

Does red on a radar mean a tornado?: No. Red indicates a strong reflectivity return, usually heavy rain or a thunderstorm core. Tornado detection relies on velocity data and on warnings issued by the National Weather Service.
Why does radar show rain when it is not raining here?: The radar beam rises with distance as the earth curves away. Far from the radar it may be sampling precipitation high in the atmosphere that evaporates before it reaches the ground.
Can radar tell rain from hail?: Not reliably from reflectivity alone. Hail is large and dense and returns energy very strongly, so it can appear as the same intense colour as the heaviest rain.

The radar page shows official National Weather Service reflectivity with the government's own colour key beneath it.

Open the interactive radar

Related guides

Categories and definitions on this page follow the National Weather Service and the Storm Prediction Center. For the official text of any product in effect, see weather.gov.