Winters in the high desert aren't as brutal as in, say, Minnesota, but temps can drop into the single digits (F) overnight. If you factor in wind, it can get pretty miserable. Nevertheless, I use bikes as my main form of daily transport, so unless it's pouring buckets or the streets are one solid sheet of ice (both of which are rare), I just ride anyway. There is no such thing as bad weather, there is only inappropriate clothing.