How to read weather radar
Weather radar shows where precipitation is falling and how hard. Once you know what the colors and shapes mean, a radar loop tells you what is coming and how soon.
What radar actually measures
A Doppler radar sends out pulses of microwave energy and listens for the echo bouncing off raindrops, hail, snow — and sometimes birds, bugs or debris. The strength of that echo is called reflectivity and is measured in dBZ. Bigger and more numerous targets return a stronger echo, so higher dBZ means heavier precipitation.
| dBZ | Usual color | What it usually means |
|---|---|---|
| 5–20 | Light blue / gray | Drizzle, very light rain or snow — or non-weather targets like bugs |
| 20–35 | Green | Light to moderate rain |
| 35–45 | Yellow | Moderate to heavy rain |
| 45–55 | Orange / red | Heavy rain, gusty thunderstorms, small hail possible |
| 55–65 | Red / magenta | Very heavy rain and hail likely |
| 65+ | Pink / purple / white | Large hail is likely in the storm core |
Color scales differ between apps. TALON uses the official NWS reflectivity scale in 0.5 dBZ steps, and tapping anywhere shows the exact value and rain rate.
Always look at the loop
A single image shows where rain is; the loop shows where it is going. Watch a storm across several frames to judge its direction and speed, and whether it is growing (more red and purple) or weakening. TALON draws each storm cell's path and estimated arrival time for your location, and the striped part of the timeline is a short-term forecast of where the rain will move next.
Storm shapes worth knowing
- Squall line — a long line of storms. The main threats are damaging straight-line winds and brief tornadoes along kinks in the line.
- Bow echo — part of a line bulges forward like a bow. Expect damaging winds near the tip of the bow.
- Supercell — an isolated, long-lived storm with a rotating updraft. Supercells produce most large hail and strong tornadoes.
- Hook echo — a hook-shaped appendage on the back side of a supercell, wrapped around its rotation. More on hook echoes.
What radar can't see
- Beam height. The radar beam climbs as it travels because the Earth curves away below it. Far from the radar it can pass over low clouds and the bottom of storms. Each NEXRAD station page lists how high the beam is at different distances.
- The cone of silence. Right above the radar the beam can't point high enough, so a second nearby radar fills in.
- Clutter and blockage. Hills, buildings, wind farms and even bugs or birds can show up as echoes, and mountains can block parts of the beam.
Going further: velocity and debris
Reflectivity tells you how much is falling. Doppler velocity shows how the air is moving — which is how forecasters spot rotation — and correlation coefficient can confirm a tornado is throwing debris into the air.
Quick answers
What does dBZ mean on weather radar?
dBZ is the unit of radar reflectivity — how strongly precipitation reflects the radar signal. Around 20 dBZ is light rain, 40 dBZ is heavy rain, and 60 dBZ or more usually means hail.
What do purple and pink mean on radar?
On most reflectivity scales, pink, purple and white are the highest values — usually large hail inside a strong thunderstorm core.
Why does radar show rain when it isn't raining?
The beam may be detecting rain high up that evaporates before reaching the ground, or non-weather targets such as insects, birds or ground clutter.