Hi
Our country wide Met Service shows a clothing layer value for each city. My city is here
https://www.metservice.com/towns-cities/locations/christchurch, currently it is 10.2 degrees C and it says 2 layers and 0 wind proof (at my house there is no wind at all).

Earlier morning like 7am it said 3 to 4 layers and at least 1 wind proof layer even though the temperature was about the same. But the sun had not risen and pretty much no wind.
I am wondering how they calculate this?
They did explain a
simple formula about 10 years based on Steadman’s Clothing index (1971) but this would have said 1mm of clothing this morning which is if anything 1 layer this morning so they have updated their formula.

Has anyone seen a formula for this, I like the idea of displaying this on my own site as I guess others would as well.
Chris