Radar gaps a concern as severe weather season opens
In March 2012, a tornado near Charlotte, N.C., damaged or destroyed nearly 200 homes, injuring four people, including three children. In February 2020, a tornado near Demopolis, Ala., destroyed a mobile home, killing a 54-year-old substitute teacher and injuring her husband. In May 2022, a violent thunderstorm complex sweeping through Minnesota killed a 63-year-old volunteer firefighter when a grain silo blew over onto his vehicle.
All three severe weather episodes share a common trait: They formed in areas of poor radar coverage known as “radar gaps,” where the closest radar is too far away to reliably detect tornadoes, flash flooding, heavy snow and ice.
That means people either were not warned by the National Weather Service about the dangerous conditions, or they weren’t warned until after the damage was done.
The U.S. weather radar network is considered the most advanced in the world. But these gaps have persisted for years, in both rural areas and highly populated cities, leaving millions of people vulnerable to severe weather as peak tornado season approaches next month.
Local and state officials, meteorologists, universities and the private sector have ramped up efforts to reduce radar blind spots, even after a 2020 Weather Service report to Congress that played down their significance. Those efforts, which in some cases began more than a decade ago, have been buoyed by pressure from lawmakers to close the gaps and by the availability of a new radar service from a tech company. In some regions, though, progress remains elusive.
“We’ve run into some roadblocks, partly because I think there’s denial of the problem,” Van Denton, chief meteorologist at the Fox affiliate serving North Carolina’s Piedmont Triad region, said in an interview.
Around the world, thousands of sensors constantly monitor weather — from the ground, ocean, air and space. Yet one meteorological instrument remains paramount for detecting hazardous, sometimes life-threatening storms: Doppler radar.
A Doppler radar sends a beam of energy into the atmosphere as it rotates to scan in all directions. The beam bounces off precipitation particles and returns to the radar, helping meteorologists track precipitation, wind, thunderstorms, and the likelihood or presence of a tornado.
The Weather Service operates a network of 143 Doppler radars covering most of the contiguous United States. An additional 16 radars are located in Alaska, Hawaii, U.S. territories and military bases.
There are dozens of regions, however, where the beam from the closest radar scans too high in the atmosphere to see certain types of severe weather. A radar beam travels in a straight line slanted slightly upward, while the Earth curves down and away from the beam. So the farther away the beam is from a radar, the higher in the sky it scans. Also, mountains can block the path of a radar beam.
In 2017, Congress directed the Weather Service to examine how low-level radar gaps affect warning accuracy.
The 2020 Weather Service report acknowledged regions where the closest radar can’t scan below 6,000 feet — potentially missing tornadoes, heavy rain and other hazardous weather at lower altitudes — but found no “significant negative impact” on tornado- or flash flood-warning performance because “trained forecasters are able to overcome aspects of reduced radar coverage” by using information from satellites, models, storm spotters and other sources.
Ajay Mehta, director of the Weather Service’s Office of Observations, told The Washington Post the conclusions from that report are “still valid.”
Still, the findings surprised some meteorologists in the private sector and academia, who were critical of the report.
“I never agreed with the report at all,” meteorologist Craig Ceecee said in an email. Ceecee has identified more than 30 populated regions affected by low-level radar gaps.
He said there are populated communities — places with more than 25,000 or even 100,000 residents — that could be at high risk for tornadoes, but where the closest radar scans at 10,000 feet or higher.
“At that point, you’re looking two miles into the atmosphere, high enough to miss many tornadoes.”