Wowser. I bottomed out at 41 early this morning around 3:30 am, with clear skies and no wind. When I came down for coffee around 4:20 am it was still at the 41 F mark. Then apparently a few puffs of wind mixed it out somewhere between about 4:30 - 5 am, warming me up to the mid-40s.
Currently 45 and clear with dp 40. If the 40s from yesterday morning didn't start to trigger a leaf change, this morning certainly will get the attention of some trees. I know that the Norway maples spread all over the woods here are usually the last to color up though, but I have seen locusts around the area that have lots of tendrils of yellow leaves.
We usually had our "first big drop" of leaves around here just before Halloween, with a 2nd drop sometime in mid-November, and whatever is left by the end of November (the city would wait until about the 1st week of December to vacuum up the leaves in certain neighborhoods - notably here - around that time). I think it is supposed to warm up a bit the rest of the week though.