Are you using an electronic ignition? Some units are sealed (i.e potted), others are not. Could be moisture getting in as the temperature changes during the course of the day.

Another thing to check is the HEI module on the distributor. Although it was not temperature related, I recently had an issue with no spark and checked everything until I determined it was the HEI. I replace my unit with one from Pertronix.

Note that you will need a special tool to remove the two screws that hold the HEI module in place, which you can get from Summit Racing, etc.