Using these radars, forecasters can spot the existence of a tornado by detecting airborne debris lofted by the twister’s circulation. They can track the all-important rain-snow line in winter storms and even spot smoke plumes from severe wildfires. But as capable as the U.S. radar network is, gaps in coverage have drawn consistent complaints from meteorologists and lawmakers frustrated by unwarned-of severe weather.
Now, an overdue report to Congress from the National Oceanic and Atmospheric Administration (NOAA), which operates the National Weather Service, attempts to quantify the impacts of such gaps on warning performance. The results downplay the significance of the gaps, counter to the experience of some public- and private-sector meteorologists.
Several meteorologists said the congressionally mandated report inadequately addresses the true impacts of these gaps, describing its methodology as inadequate and incomplete and its conclusions as “disappointing” and even “offensive.”
The gaps, which the report identifies in some detail, occur in locations so far removed from radar sites that the beams emitted by the radar overshoot the weather they are intended to detect. The greater distance a location is from a radar site, the higher in the sky the radar scans for trouble.
The Charlotte metro area, home to about 2.6 million, is served by a Doppler radar 80 miles away in Greer, S.C., and the radar beam intersects clouds at about 5,000 feet or more above the city, missing some of the most important low-level weather features that can determine whether a storm will spawn a tornado. During the winter, some snow and ice events can take place largely below the height of the beam.
Other cities have far more coverage, including Washington, for which there is a Weather Service Doppler radar in Sterling, Va., as well as less powerful radars situated near the region’s three major airports and Joint Base Andrews. With radar beams reaching clouds at altitudes below 3,000 feet over the city, meteorologists have the ability to see the lower levels of storms, which is where tornadoes tend to form.
Radar gaps have been a contentious issue in the weather community for years, not only in Charlotte, but also in the Pacific Northwest, where spotting dangerous weather moving in from the Pacific is especially important.
Weather Service finally responds to Congress but says there’s no problem here
In a 2017 bill, Congress directed the Weather Service to examine how radar gaps affect warning accuracy and report to Congress within less than a year. Separately, Congress asked for a report on warning performance associated with radar coverage where the beam is 6,000 feet above ground level and higher.
Long past congressional deadlines, the radar gaps report was released in September to address both congressional requests, and it contains some surprising findings.
Instead of concluding that radar gaps make a difference in severe weather detection and warnings, as many meteorologists strongly suspect, the Weather Service told Congress that they make little to no meaningful differences in warning performance.
“Poor radar coverage is never the single contributing