you need to go read an article in IFR Magazine about this - AOPA also has the letter from the FAA and their response on their website
aopa.org/whatsnew/newsitems/ … icing.html
they complain about the idiot who wrote the letter . . . the definition apparently is now ‘high humidity’ whatever that means.
The AIM states that visible moisture and below freezing temps create the potential for icing. In the ‘real world’ where we fly, it is much more complicated than that. I have flown at night IFR in a blinding snowfall and not picked up even a flake of ice, and likewise flown into a thin cloud I could see though and picked up a quick 1/4" of rime.
At temps that far below freezing - Minus 17C is 1F - the chance of snow sticking to an air frame that cold is fairly low. Take that same airframe, and have it be at 0, 1, 2 or 3C and fly it through rain or snow, and it’ll stick fast.
Drive a car through moderate snow at 32F, the snow will stick everywhere and the wiper will get coated. Drive that same car through snow at 15F and it not stick to anything. Same concept.
That being said, you have one mile visibility in snow and blowing snow and there are small airplanes flying around? Perhaps on an instrument approach, but just flying in the pattern? The runway must be somewhere between what 33 and 35 with winds like that as well? Just cause someone is doing it does not make it safe …