A tweak to the National Weather Service radar could create more accurate forecasts for the Yampa Valley | SteamboatToday.com

A tweak to the National Weather Service radar could create more accurate forecasts for the Yampa Valley

A proposal to lower the radar's angle could bring a bigger part of Steamboat skies into the forecast

A storm rolls in over Emerald Mountain Sunday afternoon.
Eleanor C. Hasenbeck

STEAMBOAT SPRINGS — A change as small as tilting the angle of a radar beam could mean meteorologists would be able to better forecast storms in the Yampa Valley.

Radar works by sending out electromagnetic waves. Those beams bounce off storms and other objects in the atmosphere, and in the case of weather, forecasters can use those echos to learn characteristics of a storm.

But the angle at which those beams are sent out actually means that some areas, including much of Northwest and Southwest Colorado and eastern Utah, don’t receive the most effective radar coverage, or in some portions of these areas, no radar coverage at all.

The National Weather Service in Grand Junction is considering lowering the angle at which its radar sends out its beam of electromagnetic waves.

How would this change work?  

In an ideal world, radar would send its electromagnetic waves onto a flat surface, meaning that they would travel as far as they could before bouncing off a storm.

The real world isn’t flat, though. When a radar beams out its waves, those waves are reading higher and higher elevations of the atmosphere as the Earth curves away from the beam.

That means that for areas at the edge of the Weather Service’s radar coverage, including much of Routt County, the radar sitting atop Grand Mesa near Grand Junction can only capture information about storms in the higher levels of the atmosphere.

Imagine if you placed a pin with a string attached to it to a tennis ball. If you pull that string straight and taught, the farther away the string got from the pin, the farther away the string would get from the curved surface of the ball. The pin is the radar, and the string is its beam.

This illustration shows the impact of the earth’s curvature on how radar systems can read a storm.
Courtesy National Weather Service in Birmingham

Right now, the Weather Service sends out a radar beam at angles between 0.5 and 19.5 degrees, meaning it’s already pulling the string up and slightly away from the ball. By lowering the angle that the radar sends out those waves, the Weather Service could pull that string lower and closer to the ball, meaning that forecasters could see lower elevations of the atmosphere for a greater distance.  

The Weather Service has proposed lowering that minimum scan angle from 0.5 to -0.2 degrees.

“Basically, by lowering that elevation scan, it’ll allow us to see more of the atmosphere,” said Jeff Colton, the warning coordination meteorologist at the National Weather Service in Grand Junction. “We’ll be able to see farther out with our radar than we normally would like, in are some examples of the coverage areas on our online.

According to an environmental assessment, lowering that scan angle by 0.7 degrees could expand radar coverage from 9,172 square miles at 2,000 feet above the radar site level to 29,006 square miles — a 216% increase in low-level radar coverage.

“It’ll be an improvement, especially for eastern Utah and Northwest Colorado,” Colton said.

That low scan will still be blocked from reaching much of Routt County —mountains get in the way — but it’ll give forecasters a better idea of what’s going on at lower altitudes of eastern Utah and Moffat County, where much of Routt County’s weather develops. At higher altitudes, the lower scan angle is anticipated to expand radar coverage to much of Routt County.

“With that information, we’ll be able to tell the strength of storms,” Colton said. “Speed of motion will be more accurate. (Forecasters will be able to tell) what type of precipitation is falling out of them, how much is falling out of them and ice content — how large potential hail will get — and things like that. We’ll be able to see a lot more of the storms and than what we can see now.”

Colton explained that the change doesn’t require any changes to the operations or hardware of the radar; it’s just different software.

“We’re not changing the tower at all. It’s all the same,” he said. “It’s just simply telling the radar that it can now go below 0.5 degrees.”

What would more radar coverage mean for our forecast?

This means forecasters will be better able to predict aspects of a storm, such as precipitation and rotation. During last year’s brief and nondestructive tornado over north-central Routt County, forecasters couldn’t see low-lying rotation in the storm on the radar — only broad, high-level rotation.

Ski Town U.S.A. will be pleased to hear that this will also improve forecasters ability to predict winter weather.

“It will really help with wintertime precipitation as well because that tends to be shallower and lower to the ground,” Colton said. “Right now, our radar overshoots most of that, but with this, we will hopefully be able to pick up a lot more snowfall in the wintertime.”

The proposal is currently undergoing National Environmental Policy Act Review. The bulk of this analysis focuses on the impact of lowering the beam of electromagnetic waves would have on items and process that could be impacted by the waves. A draft environmental assessment considering the change found that the change would have a low risk of significant effect for a number of items that can be impacted by electromagnetic waves, including radio, television and telephone signals, explosive devices, fuel handling, implanted medical devices and astronomical observatories.

More information about the proposed change, including how to submit public comment and the entire draft environmental assessment, can be found online at weather.gov/gjt/radarchange. The Weather Service is accepting public comment on the proposal until Wednesday, Sept. 18.

To reach Eleanor Hasenbeck, call 970-871-4210, email ehasenbeck@SteamboatPilot.com or follow her on Twitter @elHasenbeck.

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