WMBF Investigates: Weather radar beam blocked by trees, impacting its ability to detect storms

WMBF Investigates: Weather radar beam blocked by trees, impacting its ability to detect storms

HORRY COUNTY, SC (WMBF) - The National Weather Service’s radar is a powerful tool, but only if it can get the information it needs to help predict the weather.

“Something that is blocking the beam from progressing down that track as it’s going around and interrogating the atmosphere,” said Steven Pfaff, a meteorologist with the National Weather Service.

That’s an issue with the radar that covers our area, located in Shallotte, N.C. The radar’s beam is being blocked, which impacts its ability to accurately detect storms around the Grand Strand. The radar works by sending out signals through the atmosphere, much like a bat uses echo location. But as the trees continue to grow, they have blocked some of that signal from reaching the storms. That can make it more difficult to detect things like rotation within a storm, often a sign of a developing tornado.

“Weather Service takes seriously because we need the data to be able to do our job effectively. Issue forecasts, issue warnings,” Pfaff said.

So why don’t they cut down the trees responsible for the problem? A study contracted by the Radar Operations Center, a division of NOAA, found that wasn’t a reasonable solution.

“So many different land owners in the area,” Pfaff said. “It’s their business what they do with their land and unless there was a coordinated effort, then that would probably take several years to do. We can’t wait several years.”

Other options were explored, including raising the current radar or moving the radar to another location. The question then becomes the cost, which could be as much as $5 million. Raising the radar would only be a temporary solution as the trees continue to grow and it places the radar at a higher risk of damage from land falling hurricanes.

So, what are some other solutions?

“What the signal loss is, and you know what that is, which can be calculated, then you can apply that boost to show what is should look like,” Pfaff said.

Another suggestion is to use data from other radar to fill in the gaps in information created by the trees blocking the beam. Because while the radar in Shallotte is our closest radar and provides the best coverage of the Grand Strand, there are others across the Carolinas. We have two other radars that cover our area, including ones near Charleston and Columbia. While their beams do reach the Grand Strand, by the time the signal reaches our area, it’s scanning nearly 15,000 feet up into the storm.

The curvature of the earth means the further you are away from the radar, the higher it's scanning. When using these distant radars, we miss critical data, like how much rotation is in the lower levels of the storm, important for forecasting tornadoes.

It is possible to lower the angle which these radars scan, enough so to give us coverage all the way down to 3,000 feet, a significant improvement.

This lowering of the radar scans is something that’s being explored by the Radar Operations Center, but it depends on an environmental assessment that needs to be done but currently isn’t funded.

Copyright 2018 WMBF. All rights reserved.