What happened to the concrete min?

Figure 1

At a number of places there was a touch of ground frost this Friday morning (fig 2), nothing very unusual in this for early October, and although its measured with what’s called a grass minimum thermometer, it was never called a grass frost even though it’s usually over grass where the lowest temperature occurs and where a frost is most clearly visible. In my days as an observer, we always laid a thermometer on a paving slab and measured the concrete minimum, which was usually, but not always a wee bit higher that the grass minimum. I wonder if that’s still being done?

Figure 2