Shampoo (as needed based on scalp condition, build up etc) usually bi-weekly. I'm a CWer though. I Co-wash 2 to 3 times a week year round. I actually have to do it (CW) more in the winter b/c of dryness from wearing hats, scarves, indoor heat, cold drier air outside etc.
. Like Dposh167 said, I try not to go outside with my hair too wet but sometimes do. If I do I have a scarf, followed by toboggan and then a hat on too depending on the temp. I have learned to layer my hats just like I layer my clothes in the winter...