Buzz
Can you imagine life without weather radar? This unintended breakthrough changed the way we observe weather patterns, saving countless lives in the process. From observing light rainfall moving towards us to pinpointing a tornado's exact path as it devastates communities hundreds of miles away, weather radar has been indispensable. It's an extraordinary technology, and understanding how to interpret the colors on the map can keep you safe, especially as we head into severe weather season.
THE OPERATION
During World War II, soldiers on the front lines noticed that the radar they used to detect enemy aircraft also picked up rainfall, allowing them to monitor both weather and enemy planes simultaneously. After the war, meteorologists studied this discovery and transformed it into the life-saving tool we rely on today.
The United States operates over 120 weather radar stations across the country, constantly monitoring the skies to ensure our safety from any weather event that may arise. Weather radar systems feature a rotating dish encased in a large white dome; this dish emits pulses of energy (the radar beam) into the air to detect weather phenomena like rain or hail. When the radar beam encounters an object, some of the energy reflects back, returning to the radar site.
PRECIPITATION
A radar image showing Hurricane Katrina as it made landfall east of New Orleans on August 29, 2005. (IMAGE: Gibson Ridge)
The strength of the returned radar beam and the time it takes for the pulse to return help us gauge the intensity of the precipitation and its distance from the radar site. The data is then displayed on a map using a color scale, typically ranging from light blue to dark red and purple. Cooler colors represent lighter precipitation, while warmer colors indicate heavier precipitation. Solid areas of orange, red, and purple usually signify intense thunderstorms.
A recent advancement in radar technology, known as "dual polarization," enables the radar to emit two beams of energy—one horizontal and one vertical. This allows us to analyze the size and shape of the objects falling through the air. This innovation helps us distinguish between rain, hail, snow, sleet, and debris from tornadoes. The National Severe Storms Laboratory refers to this as "the most significant enhancement ever made to the nation's radar network since Doppler radar." (Doppler radar detects an object's velocity, as explained below.)
The main limitation of dual polarization technology stems from the Earth's curvature. As the radar beam travels further from the radar station, it rises higher off the ground due to the curvature of the Earth. Once the beam reaches several dozen miles away, it can only detect precipitation that is more than 10,000 feet above the surface—too high to accurately assess what’s happening near the ground.
VELOCITY
A side-by-side radar image of the Tuscaloosa-Birmingham tornado on April 27, 2011. The left panel displays precipitation, including the debris ball within the tornado, while the right panel illustrates the winds inside the storm. (IMAGE: Gibson Ridge)
One of the most crucial features of weather radar is its ability to utilize the Doppler effect, which allows the radar to detect the speed and direction of moving precipitation—in essence, it shows us the winds. The National Weather Service began using this technology in the 1980s, enabling the detection of damaging wind gusts and the formation of tornadoes within thunderstorms.
TV coverage of severe weather often features velocity imagery to help meteorologists and viewers identify where a tornado is most likely to form within a violent storm. Velocity imagery typically uses red and green colors; red indicates winds moving away from the radar site, while green represents winds moving toward the radar site.
When the red and green colors on a radar image are positioned closely together within a thunderstorm, it forms a rotational couplet, indicating that a tornado is likely occurring. The couplet in the radar image shown above represents the winds rotating around the powerful EF-4 tornado that devastated Tuscaloosa and Birmingham, Alabama, on April 27, 2011.
NON-PRECIPITATION RETURNS
Radar isn’t just limited to detecting precipitation; it can also help identify tornado debris. This is a critical tool for confirming the presence of tornadoes, especially when heavy rain or darkness would otherwise make such identification impossible. Radar can also pick up other phenomena, like smoke from wildfires, insect swarms, flocks of birds, weather fronts (such as cold fronts and sea breezes), and even tragic events like the disintegration of the Space Shuttle Columbia over Texas in 2003.
Radar has become so deeply embedded in meteorology that it seems like it’s always been around. However, it's important to remember that it is a constantly advancing technology, with future uses that are still unknown.
