I can't remember the links, but lots of research is indicating that stretching before exercise does NOT reduce injury, but that warming up (i.e. going slowly at the start of activity) does. Joint pain that is weather sensitive is very suggestive of arthritis, which may not respond much to cool muscle stretching. The good news is that if you keep the joint warm (knee warmers or tights) below 50, some say 60, degrees F; the smooth ROM repetition of cycling is good for the joint, helping to maintain joint flexibility. Some people do well with the chondroitin sulfate + glucosamine supplements. Be sure your gearing is low enough that you can sit and spin up those hills. Also consider a professional bike fitting to be sure you are protecting your knee's. Finally, go to your M.D. and make sure that you have osteoarthritis not rheumatoid, as the treatment is different. Good luck, and keep riding.
P.S. I really like your avatar.