With lower temps the pressure generated by the powder is less, not usually a large amount but enough to change the harmonics in the barrel. This change in harmonics will cause a change in POI. This reduction in pressure will also yeild slower velocities.
I have noted this on more than one occasion with my varmit rifles. Worst problem I ran across was loading a hot varmit round in the middle of winter then tripping that same load thru the gun in the heat of summer. The pressure spiked very high, caused the bolt to be heavy to open. The primers also started showing high pressure signs, crowning around the firing pin dimple. The round also delivered higher velocities numbers at the chronograph.
In your case the opposite is happening. The load is not quite as hot in cooler temps. The loss in velocity shouldn't be great but the change in harmonics can change POI quite a bit depending on the gun.
With a change in powder as small as half a grain I have seen POI change, this half a grain was not enough to change the velocity any noticable amount. What I'm getting at, you may not have lost much velocity but the harmonics have changed enough to influence POI. Although velocity may have dropped off more than you may like. Only a chronograph will tell the whole story.
Don't worry about velocity so much as the most accurate round you can find for your gun. All guns have their favorite combinations and will move around some when temps change. Like anything else, experiment with loads and shoot throughout the year. The gun will show you what it likes.
