what would cause the outdoor temp to climb 5-10C above the correct reading?

Recently, I noticed the outdoor temp as shown in the instrument cluster sometimes climbs as high as 45C when the outside temp is actually closer to 35C. The last 2 times, I noticed it was happening when I was in a parking garage or stop-go traffic. Sometimes it drops after I get moving at 30-40MPH, but not always.

The car seems to be running fine and the coolant temp gauge is steady. Any thoughts?