How to read a weather radar map
A radar map shows where rain and snow are falling now and, when animated, which way they are moving. This guide explains the colors and the motion.
What the radar measures
A weather radar sends out a pulse and listens for the echo that bounces back from raindrops, snowflakes, and hail. Bigger and denser drops reflect more energy. The map colors that returned energy, so brighter colors mean heavier precipitation. The National Weather Service explains its radar network in its radar FAQ.
The colors
Most radar maps use the same order of colors.
- Green. Light rain or snow.
- Yellow. Moderate rain.
- Orange and red. Heavy rain, often thunderstorms.
- Purple, pink, or white. Very heavy rain or hail.
The radar cannot tell rain from snow on its own. In winter, read the temperature with the map. Bold Weather’s radar uses a short set of colors and a legend in words instead of a color bar alone.
Which way it is moving
Press play and watch the past hour. The direction the colored areas travel is the direction the weather is moving. Weather in most of North America moves from west to east, but storms can move in any direction, so watch the loop rather than assuming.
Now, the past, and the future
The past part of the loop is what the radar saw. The future part, when a map offers one, is an estimate made by moving the current picture forward. It is useful for the next hour and less reliable after that. A forecast for later in the day should come from the hourly forecast, not from the radar.
Distance and time
Rain 30 miles away moving at 30 miles per hour reaches you in about an hour. Most radar maps have a scale bar. Bold Weather’s radar writes the next hour as a sentence from the minute forecast, such as “Rain reaches you in about 20 minutes and lasts about 40 minutes.”
What this means for Bold Weather
Bold Weather’s radar has a large play and pause button, one time slider, a legend in words, and a sentence that says what is coming. Read about the radar or learn about the TestFlight beta.