Forecasters disputeNOAAreport on radar gaps

WASHINGTON — Weather forecasters around the country strive to warn communities in advance of every tornado that touches down, each flash flood that is about to occur and each winter weather event.

One of the most reliable and costly tools at a meteorologist’s disposal for issuing watches and warnings is a network of159 Doppler radars located across the country that provide detailed views inside storms. Radar helps meteorologists determine precipitation type and intensity, howmuch rain or snow has fallen, as well as the wind direction and speed atwhich precipitation is moving within a storm.

Using these radars, forecasters canspot 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 severe weather.

Now, an overdue report to Congress from the National Oceanic and Atmospheric Administration, which operates the Weather Service, attempts to quantify the impacts of such gaps onwarning 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 beamsemittedby 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 if 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 the District, there is aWeather ServiceDoppler radar located 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 theweather community for years.

In a 2017 weather bill, Congress directedtheWeather Service toexamine

howradar gaps affectwarning accuracy and report to Congress within less than a year. Separately, Congress also 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 reportwas released in September to address both congressional requests, and it contains some surprising findings.

Insteadof 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 factor to an unwarned event,” the study found, instead blaming a cascade of factors including human errors for causing missed warnings.

For its analysis, the Weather Service study examined the 10year warning performance at all NWS offices nationwide for tornado

and flash flood events. In total, the report looked at more than 12,000 tornado events and more than 30,000 flash floods from 2008 to 2016, and then compared events that took place within areas of dense radar coverage versus those that did not.

The radar gap study found no “significant negative impact” to warning performance that could be “tied directly to radar coverage where the beam is higher than 6,000 feet above ground level.”

“That evidence does not mean radar isunimportant, rather it suggests that there is significant, usable radar data above 6,000 feet and other information employed by forecasters to issue warnings,” the study states.

The reason, the report says, “is that humans issue the warnings, not the radar.”

There’s enough radar data that can be gleaned above that altitude and other weather information, from surface reports to satellite imagery, that makes up for radar gaps, the weather agency told Congress.

According to Rich Thompson, a meteorologist at NOAA’s Storm Prediction Center in Norman, Okla., ongoing research he’s involved in shows that tornado warning performance “generally drops off once you go beyond about 50 [nautical miles] from the radar (or above about 4,000 ft).” This decline in skill is especially the case for weak and short-lived tornadoes, said Thompson, who was not involved in the radar gaps report.

“It would certainly be easier to detect possible tornadoes more consistently ifwe had radar coverage that allowed us to see the low levels everywhere,” he said.

MatthewKumjian, a meteorology professor at Penn State University, said the methods used in the study aren’t particularly revealing because they did not assessweather forecast office performance in areas that have large data gaps versus the offices that are well-covered. He said the tone of the report’s summary struck him as aggressive, and “suggests an underlying agenda.”

Several meteorologists in the private weather sector were critical of the report as well, questioning its methods and conclusions.

Jonathan Porter, a vice president and general manager at the private forecasting firm AccuWeather, said he was “disappointed” by its conclusions.

“This report seems to glossover and over-simplify the challenging situation forecasters face each time severe weather approaches a known and well-documented radar gap tothe detriment of public safety,” Porter said in an email.

Porter said AccuWeather provided its own report to congressional committee staff in 2017 on the top 20 radar gaps nationwide, including southern Iowa and Charlotte.

Congress may take action to fill radar gaps, but nothing concrete has been proposed.“Myofficewas approached on this issue several months ago and we will continue to consider possible solutions,” said Rep. Ted Budd, R-N.C., in a statement. Budd represents a district situated between Charlotte andWinston-Salem.

Matthew Cappucci/ Washington Post A rotating supercell thunderstorm takes on a “mothership” appearance as it moves south of Lakin, Kan. A report has been released on gaps in radar coverage and weather accuracy.