How to Read Weather Radar Like a Pro
If you're going to be outside, get yourself a good weather-radar app and learn how to use it
Spring is here, and that means warmer temperatures. It also means we have to be prepared for the threat of tornadoes, large hail, damaging winds, and floods. But bad storms don’t take us by surprise as much as they once did, thanks to weather radar.
Weather radar works by sending out two perpendicular beams of microwave radiation into the atmosphere. Some of the radiation reflects off objects in the atmosphere—rain, hail, snow, you name it—and returns to the radar. Software measures the strength of returning radiation and how long it took to bounce back in order to determine the location and intensity of the precipitation. The shape of the beam, which resembles a plus sign if you look at it head-on, also allows the radar to detect the size and shape of the objects it detects, which is useful in spotting hail and tornado debris.
The best way to stay safe from dangerous weather, whether you're hiking or hanging out at home, is to invest in a good radar app for your phone and learn how to read what it’s telling you.
Look at More Than Just Precipitation
Just about everyone who’s ever used a weather app or watched a weather forecast on television knows the basics about spotting precipitation on weather-radar imagery. Most color scales are simple rainbows, and warmer colors indicate heavier precipitation.
However, just looking at the precipitation alone won’t tell you everything you need to know about a storm. A patch of dark red moving toward your location means there’s a thunderstorm on the way. A line of heavy precipitation moving in unison is a sign of a squall line that could pack gusty winds.
A storm that looks like a fishhook is particularly concerning. The image above shows a classic supercell—a thunderstorm with a rotating updraft—in Alabama on March 3. The rotating updraft allows the storm to produce large hail, high wind gusts, and strong tornadoes. This particular thunderstorm produced an EF-4 tornado with estimated winds of 180 miles per hour. (EF refers to the Enhanced Fujita scale, which rates tornado damage from 0 to 5.)
Know What's Going on Inside a Storm
In the 1990s, weather-radar technology developed enough to let us see the winds within a thunderstorm. By using the Doppler effect to measure how fast and in which direction rain, hail, and snow are moving, it can accurately tell us the wind speed and direction of a storm. Velocity imagery is critically important, because it tells you what’s going on inside of a storm, something you wouldn’t inherently know just by looking at the precipitation. This technological advance has saved countless lives over the past couple of decades.
The tornado that hit Greensboro, North Carolina, in April 2018 is a great example of why it’s so important to look at the wind within a storm. The following radar image shows precipitation within the line of thunderstorms while the EF-2 tornado was in progress.
Nothing appears too suspicious, right? But looking at the rain alone is deceiving. It becomes apparent that there’s a tornado on the ground once you flip over to velocity imagery and look at the wind swirling within the storm.
Velocity imagery is almost always displayed with red and green colors. Red shows winds blowing away from the radar, and green shows winds blowing toward it. Stronger winds usually equate to brighter colors on the radar imagery. You can spot rotation and a possible tornado in a thunderstorm by looking for strong winds blowing in different directions right next to each other. Bright colors all moving in one direction are a sign of damaging straight-line winds like you’d see in a squall line.
Recognize the Limits of Radar
Like any technology, there are limitations. Mountains are a significant barrier to radar use in the western United States. Vast swaths of land in Oregon, Nevada, and Utah have little useful radar coverage at the lower levels of the atmosphere due to the region’s rough terrain, which can make it more difficult to spot hazards in these areas.
The height of the radar beam itself also presents a challenge. The beam rises higher off the ground with distance as it distances itself from the radar, because of the curvature of the Earth. This means that the radar beam is above 10,000 feet once it’s a few dozen miles away from the radar site, making it difficult to see low-level features in thunderstorms, like damaging winds and tornadoes, especially in parts of the Plains and Midwest where relatively poor radar coverage coincides with frequent thunderstorm activity.
Get the Best Radar App
You can see the weather radar on just about any weather app for your phone. Unfortunately, most of those apps are lacking in detailed radar imagery, limited to an oversmooth, nebulous blob of precipitation chugging toward your location. That can help in a pinch, but sometimes it’s just not enough—especially if you’re out hiking.
The best radar app you can put on your phone is RadarScope. This professional-level app lets you track storms just like the meteorologists—in fact, most meteorologists use the app on a day-to-day basis. The app isn’t free—it costs $10 for both Android and iOS—but it’s worth it, especially if you’re involved in activities that require close monitoring of rapidly changing weather conditions.
You have more options if you’re at home or in the office and have access to a computer. The best radar software for your computer is produced by Gibson Ridge. Programs like GR2Analyst, which is the software I used for the radar images in this article, are great for analyzing radar imagery down to the pixel, just like you’d see on television during severe-weather coverage.
Weather-related injuries and fatalities have steadily dropped over the decades due to better detection, warning, and prevention, but it’s important to frequently check the weather if you plan to spend any significant time outdoors. Even if you can track the radar like a pro, making sure you have the ability to receive and heed severe-weather warnings should always be a part of your weather-safety plan when you’re out and about on a bad-weather day.