By Sam Collentine, Meteorologist Posted 3 years ago October 13, 2020

Reading Radar, Explained

Radar shows us if there is precipitation falling through the sky and helps you to answer the question, "Is it currently or about to rain or snow?".

The radar itself is a large instrument located at the top of a tower and covered with a protective dome.

The rotating machine sends out a pulse of energy in all directions. If any of that energy hits something in the sky, it bounces back toward the radar, and computers calculate where the "something" in the sky is located and if it's rain, snow, birds, or insects (yes, all of these can show up on radar).

The colors on a radar map represent the intensity of the precipitation, which is determined by how much energy bounces back to the radar.

The color scale is presented in units of decibels (dBZ). Here's what you need to know:

Values of 20 dBZ (green) is typically the point at which light rain and snow begins.

Values of 40 dBZ (orange) is typically the point at which lightning can occur and the rainfall rate is approaching 0.5 inches/hour.

Values of 60 dBZ (red) is about the level where 1-inch diameter hail can occur. 

While every radar image that you will encounter may be different, the three dBZ values and colors listed above will provide a good scale to keep in mind when looking at the radar reflectivity and dBZ color scheme on OpenSnow.

And here are two more tidbits:

First, radar has more difficulty detecting snow compared to rain. During winter, this means that intense snow might be falling even if the radar map shows low dBZ values (blue and green).

Second, big mountains block the radar beam from detecting precipitation close to the mountain tops. During the summer, this usually is a less important issue because thunderstorms rise far above the mountain tops and the radar can detect them. During the winter, radar might show little or no snow over the mountains even if a snowstorm is raging. This is a good time to look out the window or at a live webcam.

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About The Author

Sam Collentine


Sam Collentine is the Chief Operating Officer of OpenSnow and lives in Basalt, Colorado. Before joining OpenSnow, he studied Atmospheric Science at the University of Colorado, spent time at Channel 7 News in Denver, and at the National Weather Service in Boulder.

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