Well, the largest single-day temperature drop I've had while on a bike had to be one of the many times my wife and I rode from the Central Valley in CA to the Sonoma coast. In the summer the temperature would often reach over 110F at our home and be a little cooler in the Sonoma Valley when we rode through, maybe 105F. At some point along the twenty or so miles between Santa Rosa and Bodega Bay, the temperature would invariably drop to the mid-50sF.
On a single bike trip, I remember arriving in Banff, having ridden up from Davis, CA. The day before we left it was 115F. When we arrived, it was 40F and raining. Just to rub it in, several riders from Alberta were wearing shorts and T-shirts while I had emptied my panniers of clothes and was wearing all of them.
If I get to count using a plane, with a stupid-supplement, then the temperature range is a bit larger. I flew from Sacramento to Denver and then hopped on a bus to Keystone for a conference. It was around 85F when I left, in shorts, sandals and a short-sleeve shirt. When I got off the bus at the resort, I was told to wait for the next bus which had my bag on it. It was 5F outside where I waited half and hour for my bag to arrive. Next time I'll bring a pair of socks with me.