Being a year round rider I routinely endure cold weather here in central Pennsylvania. The coldest I've ridden was a 50 mile ride at -15F. That was over ten years ago on my LX150. Unprepared, poorly attired, and pretty much stupid. The only thing I had going for me was sunshine under a clear blue sky, a hot muffler to warm hands when the headlight wasn't enough, and plenty of time.
Now in old age, last winter, I would routinely ride in any temperature down to about -5F. Single digits and teens are fine. I am much better prepared now with Tucano Urbano Muffs and Apron, electric gloves, heated grips, and better riding clothes.
Here's a picture from a ride a few years ago on the way to work at -8F. NOTE I DIDN'T HAVE THE TUCANO GEAR YET AT THIS POINT.
I learned something from that ride about cold weather. I wrote about the experience on my blog post titled
SUB ZERO RIDING EDUCATION.