Weather radar consists of a rotating dish protected by a large white dome; this dish sends pulses of energy (the radar beam) into the atmosphere to detect objects like rain or hail. If the radar beam encounters an object, some of the radiation will bounce off of it and return to the radar site.

Doppler radar is a specialized type of radar that can detect precipitation as well as the movement of small particles, which can be used to approximate wind speed. Measuring wind speed is especially important during severe weather, such as tornadoes or thunderstorms.

Precipitation Mode is used when there is rain within the operating range of the radar. The US National Weather Service’s WSR-88D radar does not determine raindrop size. When precipitation is occurring, the radar does not need to be as sensitive as in Clear Air Mode as rain provides plenty of returning signals.

Weather radar (also known as Doppler weather radar) is an instrument that sends pulses of electromagnetic energy into the atmosphere to find precipitation, determine its motion and intensity, and identify the precipitation type such as rain, snow or hail.

dBZ stands for decibel relative to Z. In short, the higher the dBZ value, the more likely it is for severe weather to occur in the form of precipitation. Values above 20 dBZ usually indicate falling precipitation.

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160 WSR-88D radars
The Weather Surveillance Radar, 1988 Doppler (WSR-88D), also known as NEXRAD, is the most advanced operational weather radar in the world. The fleet of 160 WSR-88D radars operate 24/7 to support the weather warning and forecast missions of the National Weather Service, FAA and DoD.

The Precipitation Radar was the first spaceborne instrument designed to provide three-dimensional maps of storm structure. These measurements yield invaluable information on the intensity and distribution of the rain, on the rain type, on the storm depth and on the height at which the snow melts into rain.

Precipitation intensity is measured by a ground-based radar that bounces radar waves off of precipitation. “Reflectivity” is the amount of transmitted power returned to the radar receiver after hitting precipitation, compared to a reference power density at a distance of 1 meter from the radar antenna.

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The key shows how the colours correspond to the amount of rainfall. For example, regions of yellow on the radar image indicate moderate rainfall. The time shown on the radar is local time. These rainfall radar maps are covered by Crown copyright and remain the property of the Met Office.

Modern weather radars are mostly doppler radars, capable of detecting the motion of rain droplets in addition to intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather. Precipitation type is indicated by the color – green is rain,…

With ground clutter / non-precipitation echoes removed. Algorithm which classifies radar echoes into one of seven categories: 1) warm stratiform rain, 2) cool stratiform rain, 3) convective rain, 4) tropical/stratiform rain mix, 5) tropical/convective rain mix, 6) hail, and 7) snow.

Welcome to FAQs about the National Weather Service’s new radar webpage located at radar.weather.gov and launched on December 17, 2020. We redesigned our radar viewer to improve our services to the public.