You check the forecast for the day, see a high temp of 22 degrees Fahrenheit and think "Yay! It's warm enough for only one layer!"
For those who don't know what I'm talking about,
1 layer = a long sleeved shirt (or one short sleeved shirt with long underwear underneath it) and a pair of jeans; For Wisconsinites, this is probably at about a temp of 32-40 degrees F (0-4 degrees C), or pretty much anything above freezing. Once we hit 55-60 (13-16 C), break out the shorts and t-shirts!
2 layers = long underwear on the top and bottom, a long or short sleeved shirt, a pair of jeans; probably anything between 20-32 degrees F (-7-0 C)
3 layers = long underwear on the top and bottom, a long or short sleeved shirt over that with a pair of jeans, thick sweat shirt or sweater over that; anything below 15 degrees (-9 C)
Once we hit single digits or fall below 0 (-18 C), we pretty much try to fit as many layers on as we can while still being able to move. This usually involves snow pants and a big honkin' parka. I am also not ashamed to admit that I once wore a pair of flannel pajama pants over the top of my normal long johns and jeans when I had to walk a mile to the car one -20 (-29 C) degree morning (*not* windchill).
Lower temps are usually when the winds pick up, too, making for a lovely windchill of -20 to -30 (-29 to -34 C) or more.
The layers are subject to change depending on how long the weather "spell" is. If we get a week of below zero (Fahrenheit) and then it warms up to 20-25 degrees, a number of people can be seen wandering around outside in a hoodie and a pair of jeans, no jacket. On the other hand, in the fall or spring when we have a week of nice 60 degree temps and then it suddenly drops down to 40s, we bundle up
Also, for anything that involves two or more layers, it can also be said that most of us are wearing a jacket of some sort, too.
Yes, that was kind of pointless. But informative! Kinda.