Radar is the most-used and least-understood weather tool. Most people can spot "green means rain," but a little more literacy turns radar from a colorful picture into a genuine planning instrument.
What the colors actually measure
Radar doesn't see rain directly — it fires microwave pulses and measures what bounces back. Bigger and denser water droplets reflect more energy, so the color scale is really an intensity scale. Light greens mean drizzle or light rain you can walk through. Yellows and oranges mean steady, soaking rain — the kind that ends a picnic. Reds indicate downpours, and the small purple or white cores embedded in red often signal hail. The practical takeaway: a screen full of pale green is a different afternoon than a screen with one small red core drifting toward you.
Direction matters more than coverage
The most common mistake is judging a radar image by how much color is on screen rather than where it's moving. A large but distant green mass moving away from you is irrelevant; a small red cell moving directly at you at 40 mph is your next twenty minutes. Always run the animation loop rather than reading a still image, and watch the leading edge — its speed and direction tell you when the weather arrives at your location, which is the only question you actually care about.
Storm shapes worth recognizing
A long, arcing line of storms — a squall line — brings a sharp burst of wind and rain that usually passes within thirty minutes; those are the storms that look terrifying and then clear to a beautiful evening. Isolated round cells in summer are the classic pop-up storms: intense, brief, and hit-or-miss by neighborhood. A comma-shaped hook on the edge of a strong cell is the signature meteorologists watch for rotation, and if you see one near you accompanied by a warning, that is the moment to take shelter rather than to keep watching the screen.
What radar can't tell you
Radar shows what's happening now, not what will form later — and in summer, storms frequently develop right on top of you out of a clear radar screen within an hour. It also struggles far from the radar site, where the beam is scanning high above the ground and may miss light rain entirely, and it can misread snow and sleet. That's the case for pairing radar with an hourly forecast rather than relying on either alone: the forecast anticipates development, radar confirms timing.