My front light didn't work two weeks ago in 28 degrees. Thankfully, there were no police and the area was well lit, so I could see. The red light still worked, so I could thankfully be seen. I looked at the light next morning and it was working again in the 37 degree weather. The light has worked perfectly in 31 degrees, so it seems there is a cutoff around 30. Maybe something or other freezes, and at 31 it hadn't quite had enough time to freeze. I also forgot my hat that 28 degree evening, which meant my ears hurt a lot by the time I got home.
I have been follwing Northern USA/ Canada weather and it has looked unseasonably cold.