When there is no precipitation nearby (as in, within several counties) there is no echo at that point. But as precipitation passes through, that point shows a strong echo that remains fixed relative to the land, while the mass of precipitation passes through.
I ask myself, "Self, what can cause this?" I thought maybe a waterfall could generate mist that might travel high enough to be picked up on radar, but then I thought, even Niagara Falls doesn't make a mist that travels very high, so if it's a waterfall, it would have to be a big one, big enough that it should be well-known around here like Niagara Falls is. But I checked the area on maps, and there are no big rivers nearby. So much for the waterfall theory.
So, maybe it's something man-made that is putting radar-reflective particles into the air. So I look on maps again to see if there are any industrial parks in the area or a nuclear power plant with its cooling towers or something. But no, it's like in the middle of nowhere between two small towns.
I e-mailed local meteorologist Kevin Williams about the phenomenon, but his best guess was that it may "have to do with a higher elevation and some kind of attenuation our radar signal undergoes in that area."
When I checked a USGS Digital Elevation Map of the area, I found that the elevation does reach a peak of 631 meters at 42.6727 latitude, -78.2550 longitude. But it's not like a sharp mountain or anything. There are straight roads that go right through the area. The whole area slowly varies from 519 to 631 meters and just happens to top off at 631 in only one place. Plus, way higher elevations can be found further south all over the place, and they don't affect radar images.
Finally I got the idea to check an aerial photo of the location. I found nothing of interest at the 631 meter elevation spot, but my attention was drawn to this strange sight 1.5 miles away, next to Weber Rd. The white stuff near the center of that image would appear to be some sort of mist or smoke. But what is creating it? It seems to be randomly rising from the perimeter of a pond. There are no streams connected to the pond that I can see in the photo, and none are identified on maps, so that rules out waterfalls again. But it does seem to be a water feature of some sort.
So, what the heck is it?
My web search for pages that might mention "mist" near "weber rd" in "ny" found nothing, so it's apparently not a spot of popular interest.
I remain mystified.