Is there a exterior primer that is effective below 50 deg?
Unless you hear from someone else here, I would put this question to a paint store person or someone who does alot of exterior paint work.I know there are temperature limits on paints but I've never heard how /why exceeding the limits alter the effectiveness of the product.
I recently used Olympic oil-based primer on my cedar siding when the temperature was about 45 degrees. The instructions say it can be applied at 40 degrees and above. It does take longer for it to dry, but it appears to be nicely bonded to the wood. Check your Sears store - they have a new superpaint called Weatherbeater Ultra that you can apply at 45 degrees and above, they can suggest an appropriate primer for your project.