Maybe you’ve noticed a green radar blob over Johnston on our day-to-day weather graphics. It looks like it’s always raining there.
Well, it’s actually called clutter – and it really shouldn’t be there. First, let’s talk a bit about radars themselves.
Radars work by sending out short bursts of radio waves in all directions at the speed of light. They strike rain, sleet, snow, even some structures, and terrain. And some of that energy is reflected and sent back to the radar site where it is measured to see how strong it is and whether or not it’s moving. What’s not moving is detected as clutter and is typically filtered out.
The Central Landfill is the tallest landmass in our area where the National Weather Service radar in Taunton detects clutter. The ground under it is about 320 feet above mean sea level (MSL) according to the Rhode Island Resource Recovery Corporation. The landfill itself adds 250 feet, for a total of 570 ft above mean sea level.
“In that particular situation, it looks like there’s always a thunderstorm over Johnston that’s not moving,” Joe Dellicarpini said. He’s a Meteorologist and the Science and Operations Officer at the National Weather Service Boston/Norton office.
We know the landfill isn’t moving, so then, what is the radar picking up on?
“Actually, it is the wind farm. It’s something that’s been there, probably a couple of years now at least,” Joe said.
Green Development of North Kingstown put up these seven wind turbines on a hill around 400 feet above sea level. When the blade is straight up, the turbines stand 518 feet tall. That’s over 900 feet above mean sea level, even above the state’s highest point – Jerimoth Hill at 812 feet.
“Since there are moving blades on it, on the wind farm turbine, it thinks it’s something that’s moving,” Joe said.
That movement is what tricks the radar. Normally, it’s able to filter out tall structures like buildings and hills. Radars scan at different elevations up and down in the atmosphere, and at their lowest, reach several hundred feet above the ground – clipping the top of the Johnston wind farm, but not other turbines in the state.
“Providence, we don’t really see that, and Coventry too, it’s just, probably just below the beam, enough below the beam at that point. So, I think that’s just kind of the perfect spot, unfortunately,” Joe said.
Compared to other parts of the country, we’re fortunate to have only this one area of clutter. And now, the Radar Operations Center in Norman, Oklahoma has been enlisted to help create what’s called an exclusion zone.
“We can actually define the latitude and longitude, or kind of the elevation scan that the radar’s showing where it’s located, and we can just kind of cancel it out,” Joe said.
If all goes well, the constant storm over Johnston should subside in the next few weeks or months.
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