Warmup has more of an impact in colder weather - feeling sluggish early on is normal when it is colder. In my case, my hands are often miserably cold, which clouds the rest of the factors related to performance. Most of us don't like being out in the cold and wet, so psychologically it is normal to expect we don't do as well. But, to coin a phrase, just do it! It'll feel better in the spring!