Murdie, we get very cold winters here mate, we had minus 16 on Saturday night. One thing I learned from an old WC years ago was, when it's below minus 2, never use warm water. It freezes in seconds when it comes into contact with freezing glass. Use cold water and add screenwash or whatever you add as needed.
This is only a tip for when it's below minus 2 or when it's zero but there is wind. I asume you get about the same temp up where you are as we get here in Germany. I've managed to work down to minus 6 in the past, but it usually starts getting to be a problem at minus 4.
Hope I've made sence there
