How to read weather radar colors

Updated July 29, 2026 · 5 min read

Radar colors map to reflectivity measured in dBZ. Blue and green are light precipitation around 20 dBZ, yellow is moderate near 35 dBZ, and red above 50 dBZ means heavy rain or hail. The scale is logarithmic, so each step up represents far more water than the last.

What does dBZ mean on radar?[1]

dBZ stands for decibels of reflectivity. It measures how much radar energy precipitation bounces back, which depends mostly on droplet size. The scale is logarithmic: 50 dBZ reflects roughly 1,000 times more energy than 20 dBZ, not two and a half times more.

Because bigger drops reflect disproportionately more, reflectivity is dominated by the largest particles present. A few large hailstones return more signal than a great many small droplets, which is why hail cores light up so vividly.

This site draws precipitation from real radar reflectivity rather than a forecast model, using a continuous color ramp so light rain fades out gradually instead of stepping through hard bands.

The picture in a phone app is also usually a composite of many radar sites, blended and reprojected onto one map. That is convenient, but it means the same storm can look slightly different in two apps, because each provider smooths, filters and colors the raw reflectivity in its own way.

Reflectivity	Typically means	Rain rate
5 to 20 dBZ	Drizzle, light snow, or cloud	Under 0.5 mm/h
20 to 35 dBZ	Light to moderate rain	0.5 to 5 mm/h
35 to 45 dBZ	Heavy rain, likely thunder	5 to 25 mm/h
45 to 55 dBZ	Very heavy rain, small hail	25 to 100 mm/h
Above 55 dBZ	Large hail likely	Not meaningful

Why does radar show rain that isn't falling?

Radar beams travel in straight lines while the Earth curves away beneath them, so at long range the beam samples air thousands of meters up. Precipitation detected there can evaporate before reaching the ground, an effect called virga.

At 200 km from the radar, the beam is typically sampling around 3 km above ground. In dry air beneath, rain can evaporate entirely during the fall.

Radar also picks up things that are not weather at all: flocks of birds, swarms of insects, wind turbines and, in the right conditions, the ground itself. Most public radar products filter the obvious cases, but faint speckle near the radar site is usually clutter rather than rain.

What is the bright band on radar?

The bright band is a layer of exaggerated reflectivity where falling snow melts into rain. A melting snowflake wears a coating of liquid water while still having a snowflake's large size, and that combination reflects far more energy than either the dry snow above it or the rain below it.

On a single radar site the band appears as a ring, at the range where the tilted beam crosses the melting layer. On composite maps it shows up as smooth arcs of heavier-looking rain that never verify at the ground, so a suspiciously even arc of yellow inside an area of light rain deserves some doubt.

How current is radar data?

Public radar imagery is typically 5 to 10 minutes old. The radar needs several minutes to complete a full volume scan, and the composite then has to be processed and published. A fast storm can move two or three kilometers in that time.

This map animates the last two hours of radar, which is the full history the underlying feed publishes. Watching the loop rather than a single frame is the reliable way to judge where a storm is heading.

Lightning data ages differently. Strikes appear within seconds rather than minutes, so the lightning layer on this map is always the fresher of the two, and a burst of new strikes ahead of a radar echo is often the earliest sign that a storm is strengthening.

References

Radar ReflectivityNOAA National Weather Service, JetStream, 2026

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