Check out what Petzal has to say about temperature and accuracy.
One of the factors that is not given enough credit for making the life of the rifle shooter a living hell is the effect of temperature on the rate at which powder burns, and therefore on accuracy. I got a good taste of this last week when I went to the range with Old Sure Thing, my impeccably precise .30/06.
I was shooting a load which I had worked up last summer (you do remember summer?) involving a hot charge of IMR 4831. I remembered it as being very accurate, but the groups that showed up were not. Originally, it would put five rounds in .602, but a few days ago I was hard pressed to keep three shots inside 1.5 inches.
The joker was the temperature. My meticulous records showed that I had come up with this load in August, and that the temperature was in the mid ‘70s. On the day of the dismal groups it was 23 degrees, and that 50-degree difference was enough to screw things up royally.