The change in temp yesterday was amazing. At 6:30 it was 54. It was still 54 at 6:50, but by 7:00 (ten minutes later) it had dropped to 49. By about noon it was 20 (and snowing).
Same deal here in STL, except six hours later and no snow.
I've found that if you set the treadmill incline at 0.5 degrees, it's pretty close to road running effort.