Since your garage is temperature controlled, they will be fine driving in the cold (still need to warm up) or sitting outside for a few hours. I ran an event last weekend and the temps were around 37F in the morning after the car sat overnight, took a full lap to warm up, but the tires (Cup 2s) were fine both mornings after sitting outside overnight. I just took it easy to the track and then the first lap after the car had rested for about two and a half hours before the first run.
I daily drove my Cup2's from the end of January through the rest of winter. There were several weeks where there were temps hovering in the low40's/high30's and I parked outside all day at work. Tires were fine and showed no deterioration in performance once temps moved back up in the spring. Now, that being said, I'm not advocating winter use for the tires, but they are not as fragile as some might have you believe. You should be fine if you're just moving it in and out of the garage occasionally.
If it gets too cold the tread compound can actually crack. I don't think 30 is too cold but yes the grip will definitely be decreased.
They actually can crack if the temp gets low enough. If the temp goes below the glass transition temp, that's when the cracking can happen. The transition temp depends on the compound and its impossible to say without analyzing the tire.They lose grip when cold but thats it. They don't crack. You guys are crazy.
