According to the closest Oak Park weather station, the temperature hovered just above freezing early this morning. But skies were clear, so heat radiated from the upper layers of our backyard pools. By dawn we had our first backyard ice of the fall:
If it had been cloudy, or if there had been a breeze to circulate the water in the pool, we wouldn’t have had ice. But with a clear sky and calm air, we got these fantastic ice patterns right outside our back door!
Why the triangles in the ice? I’m not sure, but that’s the pattern we got last year in similar situations. If you look at this blog post from last February, you’ll see another example of triangular-patterned ice. That post talks about “wrinkles” forming in the super thin ice — maybe triangles develop where three wrinkles intersect. Anyway, that’s a puzzle for me to work on over the next few months.