When is it too cold to paint the exterior of the ...

This depends on the paint. Ask your exterior painter and check with your local paint store to see the limitations of their specific products. Benjamin Moore says you can paint with their exterior paints if the air and surface temperature is 35 degrees or warmer. This is really cold, and fantastic that Benjamin Moore makes a product that can work in weather this cold. Most exterior paints will require the air and surface temperature to be 50 degrees and warmer.

TCM is right, But why would you want to paint in weather like this? I know some job's need to be complete before they can be signed off for reasons a builder or bank might need. But if it's not that then wait until spring.